Anthropogenic Alkaline Niches as a Habitat for Alkalitolerant Bacteria: Taxonomy, Ecophysiology, and Biotechnologically Relevant Hydrolases

Research Article | Preprint

Cite as: Nafiz, I. H., Akter, J., Akhter, K., Khan, M. S., Hasan, S., Bappi, M. S. H., Rahman, T., Faisal, I. K., Chowdhury, M. N. A., Zedny, S. A., Ali, F., Uddin, M. K., & Hossain, T. J. (2026). Anthropogenic Alkaline Niches as a Habitat for Alkalitolerant Bacteria: Taxonomy, Ecophysiology, and Biotechnologically Relevant Hydrolases. Preprint. Available at: https://www.researchgate.net/publication/401591119

Repository: researchgate.net/publication/401591119

Status: Peer‑reviewed version will be updated upon publication.

Authors & Affiliations

Iqbal Hossain Nafiz¹,² · Jasmin Akter¹,² · Khadiza Akhter¹,² · Md Sajib Khan¹,² · Shariful Hasan³ · Mohammed Sajjad Hossain Bappi¹,² · Tanjilur Rahman¹,² · Ibrahim Khalil Faisal¹,² · Mohammad Nazmul Ahmed Chowdhury¹,² · Subrina Akter Zedny¹,² · Ferdausi Ali³ · Md. Kamal Uddin³ · Tanim Jabid Hossain¹,²*

¹ Department of Biochemistry and Molecular Biology, University of Chittagong, Chattogram, Bangladesh
² Laboratory for Health, Omics and Pathway Exploration (HOPE Lab), Chattogram, Bangladesh
³ Department of Microbiology, University of Chittagong, Chattogram, Bangladesh

*Corresponding author: Tanim Jabid Hossain · tanim.bmb@gmail.com

Abstract

Alkaliphiles and alkalitolerant microorganisms—organisms adapted to growth in strongly alkaline environments—have been predominantly studied in natural alkaline habitats. In contrast, alkaline consumer products, despite frequent human contact, remained unexplored. Here, we present a systematic survey of the taxonomic, physiological, and functional diversity of culturable alkalitolerant bacteria recovered from five widely used household products: baking soda, bar soap, liquid soap, detergent powder, and talc powder. Of 100 isolates, 83 distinct taxa were delineated by 16S rRNA gene sequencing. The assemblage was dominated by Gram‑positive taxa, primarily Bacillota (54%) and Actinomycetota (29%), while Gram‑negative Pseudomonadota (17%) were mainly recovered from baking soda. Physiological assays showed that nearly all isolates grew at pH 9–10, whereas viability declined markedly between pH 11 and 12, indicating a critical survival threshold. Eighteen isolates tolerated pH 13 and were selected for further characterization; most of these displayed limited acid tolerance (≤ pH 5.0), moderate halotolerance (≤10% NaCl), and thermal tolerance up to 50 °C. Functional screening revealed widespread amylase and protease activity at alkaline pH, whereas cellulase production and bioemulsifier (oil‑displacement/E24) activity were limited to a smaller subset of isolates. Notably, Bacillus sp. BK917 displayed particularly broad enzymatic versatility. These findings demonstrate that everyday alkaline products constitute distinct anthropogenic niches that harbour ecophysiologically adaptable alkalitolerant bacteria and identify strains for biochemical and omics‑based follow‑up to elucidate mechanisms of survival in synthetic alkaline environments.

Keywords

Alkalitolerant bacteria · Anthropogenic alkaline niches · Polyextremophiles · Alkaline amylase · Protease · Consumer‑product microbiome · Biosurfactant · Household cleaning products · Enzyme biotechnology · Bacteria in soap · Microbes in detergent · Alkaline‑active hydrolases

1. Introduction

Microorganisms are the most abundant and adaptable life forms on Earth, with extremophiles thriving in conditions inhospitable to most other organisms [1]. Among these, alkaliphiles represent a remarkable group that requires a pH of 9 or higher for growth, while alkalitolerants are those capable of withstanding high pH conditions without requiring them for survival [2]. These organisms flourish in naturally alkaline ecosystems such as soda lakes, alkaline soils, and hydrothermal vents [3], where they contribute to nutrient cycling, organic-matter decomposition, metal detoxification, and the structuring of microbial communities [4]. The survival of alkaliphiles in such challenging habitats arises from sophisticated evolutionary adaptations, including cell walls enriched with acidic polymers that help maintain a circumneutral cytoplasmic pH, specialized membrane lipid compositions for structural stability, and highly efficient ion-transport systems [5]. In particular, Na⁺/H⁺ antiporters play a central role in preserving cellular homeostasis across steep pH gradients [6]. These physiological adaptations allow alkaliphiles to function as key colonizers in alkaline environments [7].

From an industrial perspective, interest in alkaliphilic bacteria has grown because many produce enzymes that retain activity at high pH, properties valuable for detergent, textile, pulp-and-paper, biofuel, and other industrial processes [8]. Among these, alkaline proteases are particularly significant, accounting for a substantial proportion of global enzyme production and exhibiting widespread applications across industries such as detergents, food processing, leather, textiles, pharmaceuticals, and waste management [9]. Similarly, alkaline amylases and cellulases are in high demand, particularly in processes requiring the breakdown of starch and cellulose under alkaline conditions, such as pulp and paper production, textile desizing, and biodegradation [10,11]. Furthermore, surface-active compounds—molecules that reduce interfacial tension and promote the mixing and stabilization of immiscible liquids—are industrially important in sectors such as cosmetics, lubricants, and cleaning products, many of which operate under alkaline conditions [12,13]. Sourcing these biomolecules from alkalitolerant microbes offers potential advantages in cost-effectiveness and sustainability [14,15].

Despite this interest, studies on alkaliphiles and alkalitolerants, their ecology as well as their biotechnological exploitation have predominantly focused on microorganisms isolated from natural alkaline habitats such as soda lakes, deserts, hot springs, and carbonate-rich soils [16]. In contrast, the microbial communities and their functional potential in human-made, high-pH products used in daily life have largely remained unexplored. Everyday consumer products such as soaps, detergents, baking soda, and similar formulations may act as persistent anthropogenic alkaline niches that harbor specialized microbial communities pre-adapted to produce alkaline-active industrially relevant biomolecules. Studying these taxa could provide insights into microbial adaptation to synthetic chemical environments and identify novel enzymes or surface-active compounds for biotechnological use. Recent studies have begun to explore extremophiles in engineered settings; for example, their isolation from industrial by-products such as bauxite residue has been reported [17]. Another study demonstrated that Cronobacter sakazakii, an alkaliphilic bacterium isolated from oil-contaminated wastewater, produced a biosurfactant with strong emulsifying activity [18]. However, to date, microbes in most commercial alkaline products remain poorly characterized beyond a few public-health–oriented studies (e.g., investigations of hand sanitizers) [19].

Therefore, the primary aim of the present study is to address this knowledge gap by characterizing culturable bacteria from commonly used alkaline consumer products. Similar to natural alkaline environments, alkaline household products may exert selective pressure that supports specialized microbial communities with unique metabolic pathways for the production of alkaline-active biomolecules. Accordingly, the objectives of this study are to (i) identify culturable taxa present in these products, (ii) determine their physiological limits by assessing tolerance to pH, salinity, and temperature stress, and (iii) evaluate their functional potential by screening for alkaline-active hydrolytic enzymes and surface-active compound production. Through these investigations, this study aims to broaden the ecological understanding of microbial life in these anthropogenic niches and the extreme metabolic capabilities shaped by their distinctive chemical environments.

2. Materials and Methods

2.1. Alkaline consumer products used for the isolation of alkalitolerant bacteria

Five types of alkaline commercial products were collected for this study: bar soap, liquid soap, detergent powder, talcum powder, and baking soda. Multiple samples of each product type were included, comprising items currently in household use as well as freshly purchased samples. For each product type, 1 g (for solid/powder samples) or 1 mL (for liquid samples) aliquots were taken from each collected sample, pooled, and mixed; 20 mL of sterile distilled water was added to the pooled material. The mixtures were shaken at 180 rpm for 30 minutes, and pH was measured.

2.2. Culture media and growth conditions for alkalitolerant bacteria

Three media were used for enrichment, isolation and maintenance of alkalitolerant bacteria: Horikoshi-I (comprising 10.0 g/L glucose, 5.0 g/L polypeptone, 5.0 g/L yeast extract, 1.0 g/L K₂HPO₄, and 0.2 g/L MgSO₄·7H₂O), R2A (comprising 0.5 g/L peptone, 0.5 g/L casamino acids, 0.5 g/L yeast extract, 0.5 g/L dextrose, 0.5 g/L soluble starch, 0.3 g/L K₂HPO₄, 0.05 g/L MgSO₄, and 0.3 g/L sodium pyruvate), and Nutrient Agar/Broth (NA/NB; Sisco Research Laboratories Pvt. Ltd., India) prepared according to the manufacturer's instructions. The pH of the media was adjusted after autoclaving by adding filter-sterilized solutions: 1 N Na₂CO₃ (for enrichment and isolation), 1 N NaOH (for stress tolerance assays), or 1 N HCl (for acid tolerance). Cultures were incubated at 30 °C in a shaking incubator at 170–180 rpm.

2.3. Enrichment and isolation of alkalitolerant bacteria

For enrichment, 1 mL of each sample mixture was inoculated into 15 mL Horikoshi-I or R2A broth adjusted to pH 9 or 10 in 60 mL test tubes, and incubated at 30 °C with shaking at 180 rpm for 5 days. Following enrichment, 180 µL aliquots from serial dilutions (5×) were spread onto agar plates (1.5–2.0% agar) and incubated at 30 °C for 2–3 days. Distinct colonies with different morphologies were selected (n = 115) and purified by repeated streaking until uniform colonies were obtained. Pure cultures were preserved in Horikoshi-I medium with 20% (v/v) glycerol at –80 °C and –20 °C. Fifteen isolates failed to revive from glycerol stocks; the remaining 100 isolates were subjected to molecular identification.

2.4. Bacterial identification by 16S rRNA gene sequencing

Molecular identification of the alkalitolerant isolates was performed using 16S rRNA gene sequencing. Genomic DNA was used to amplify partial 16S rRNA genes by PCR with universal primers 27F (5′-AGAGTTTGATCNTGGCTCAG-3′) and 1492R (5′-GCTTACCTTGTTACGACTT-3′). PCR products were sequenced and processed as previously described [20]. Raw sequences were inspected and trimmed to remove low-quality bases from both ends, then forward and reverse reads were assembled into consensus sequences using BioEdit. Consensus sequences were aligned and compared pairwise to detect identical sequence types; after removing duplications, 83 unique sequence types were retained for downstream analyses. Taxonomic assignments were made by comparing the consensus sequences to reference type strains as described in [20].

2.5. Determination of pH tolerance of the bacterial isolates

To assess pH tolerance, preculture of each isolate was prepared at pH 9. A 1% inoculum from preculture was transferred into fresh NB adjusted to the test pH and incubated at 30°C with shaking at 180 rpm. Growth was visually monitored daily for 8 days and categorized by turbidity as: – (no growth), + (slight growth), ++ (moderate growth), and +++ (strong growth). To confirm the maximum pH tolerance, isolates were streaked onto nutrient agar plates adjusted to the highest pH at which growth had been observed in broth, and examined for colony formation.

2.6. Determination of salt and temperature tolerance

Isolates were screened for salt and temperature tolerance in NB adjusted to pH 9. Salt tolerance was assessed in NB (pH 9) with NaCl at final concentrations ranging from 2% to 30% (w/v). Tubes were incubated at 30 °C with shaking at 180 rpm. Temperature tolerance was evaluated by incubating cultures in NB (pH 9) at 40 °C, 50 °C, or 60 °C with shaking at 180 rpm. Growth was monitored visually for 5 days.

2.7. Screening for alkaline-active extracellular hydrolytic enzymes in the alkalitolerant bacteria

Selected alkalitolerant bacteria were screened for the production of extracellular hydrolytic enzymes using agar plate assays with appropriate substrates following previously described protocols. The diameter of the clear zone around each colony was measured as an indicator of relative enzyme activity [20].

Amylase assay: Amylase activity was assessed at pH values ranging from 8 to 13 by inoculating strains onto starch agar plates (10 g/L soluble starch, 5 g/L tryptone, 3 g/L yeast extract, 20 g/L agar). After incubation at 30 °C for 48 h, plates were flooded with iodine–potassium iodide solution (1% iodine in 2% potassium iodide). Clear zones around colonies indicated starch degradation and confirmed amylase production [20].

Protease assay: Proteolytic activity was evaluated at pH values ranging from 8 to 13 on NA plates supplemented with 1% (w/v) gelatin. Plates were incubated at 30 °C for 48 h and inspected for clear halo zones around colonies, indicating protease activity [20].

Cellulase assay: For cellulase screening, strains were inoculated onto carboxymethyl cellulose (CMC) agar plates (10 g/L CMC, 2 g/L tryptone, 4 g/L KH₂PO₄, 4 g/L Na₂HPO₄, 0.2 g/L MgSO₄·7H₂O, 0.001 g/L CaCl₂, 0.001 g/L FeSO₄·7H₂O, 20 g/L agar) adjusted to pH 8 or 13, and incubated at 30 °C for 48 h. Plates were then flooded with Congo red (2 g/L) for 10 min and destained with 1 M NaCl for 15 min. Clear zones around colonies indicated cellulase production [21].

2.8. Screening for surface-active properties of alkalitolerant bacteria

Isolates were screened for surface-active activity by oil-displacement assay. Strains producing a positive oil-displacement halo were further assayed for emulsification capacity (E24). Cell-free culture supernatants were obtained by centrifugation at 5000 rpm for 20 min at 4 °C and subsequently filtered through a 0.22 µm syringe filter.

Oil-displacement assay: A thin layer (10 μl) of engine oil was added to 30 ml of distilled water in a Petri dish, followed by the addition of 20 μl of supernatant to the center of the oil layer. Formation of a clear displacement zone indicated positive surface-active (biosurfactant) activity [22].

Determination of emulsification index (E24): For E24, 2 ml of culture supernatant was mixed with 2 ml of kerosene, vortexed vigorously for 2 min, and left to stand at room temperature for 24 h. The emulsification index was calculated as:

E24 (%) = (Height of the emulsified layer / Total height of the liquid column) × 100 [23].

2.9. Use of language models

Large language model (GPT-4o and Gemini) were used to assist with language editing, phrasing, preliminary data summarization, and identifying potential patterns, all of which were independently verified and approved by the authors. The models did not execute experiments, collect data, generate references or make decisions regarding study design or data analysis, and are not credited with authorship.

3. Results

3.1. Diversity and taxonomic distribution of the alkalitolerant bacteria in alkaline consumer products

A total of 115 morphologically distinct bacterial colonies were isolated from five anthropogenic alkaline substrates: baking soda, bar soap, liquid soap, detergent powder, and talc powder. Fifteen isolates could not be revived from glycerol stocks, leaving 100 isolates for 16S rRNA gene sequencing. Pairwise comparison of trimmed 16S rRNA gene sequences revealed several groups of identical sequences, resulting in 83 taxonomically distinct sequence types that were used for downstream analyses. All isolates (n = 100), along with their source samples and assigned taxa, are listed in Table 1. The largest number of isolates (n = 32; 32%) were recovered from baking soda, followed by detergent (22), talc powder (20), bar soap (14), and liquid soap (12).

Molecular characterization revealed a phylogenetically diverse alkaliphilic microbial community within these anthropogenic substrates. The community comprised 24 distinct bacterial genera, exhibiting pronounced compositional divergence among individual matrices that underscores a highly source-specific community structure (Figure 1). Notably, Micrococcus constituted the core microbiome, emerging as both the most abundant taxon (n = 20) and the sole genus ubiquitously distributed across all product types. Baking soda exhibited the highest phylogenetic richness and yielded the greatest number of isolates, including the maximum number of Staphylococcus (n = 5) and Exiguobacterium (n = 7) isolates. Other genera such as Enterococcus, Bacillus, Sutcliffiella, and Stenotrophomonas were relatively abundant, while singleton taxa were frequently confined to single products (e.g., Klebsiella, Cytobacillus, Paenibacillus, Brevundimonas, Planococcus, Shouchella, Nesterenkonia, Kocuria, Mammaliicoccus, Kytococcus, and Lysinibacillus). Structurally, the community was heavily skewed toward Gram-positive lineages, predominantly within the phyla Bacillota (formerly Firmicutes) and Actinomycetota (formerly Actinobacteria). Gram-positive taxa represented 79.2% of the detected genera (19 of 24) and accounted for 85.0% of all isolated strains. Conversely, Gram-negative genera were sparse, comprising only 20.8% of generic diversity (n = 5), with Stenotrophomonas being the most prominent representative. Intriguingly, Gram-negative taxa were significantly enriched in the single-component baking soda matrix (25.0%) compared to formulated products like soaps, detergents, and talcum powder (mean 11.8%), highlighting baking soda as a distinct micro-environment for niche-specialized alkaliphiles.

At the class level, Bacilli exhibited ubiquitous dominance across nearly all substrates, with the distinct exception of bar soap, which was dominated by Actinomycetia (Figure 2). In all other sample types, Actinomycetia consistently ranked as the second most abundant class. Members of the class Gammaproteobacteria accounted for only 12% of the total isolates, with 50% of these strains recovered exclusively from the baking soda matrix. Alphaproteobacteria represented the rarest taxonomic class and were completely absent from all soap and detergent formulations.

3.2. Alkaline pH tolerance of the isolates

The pH tolerance profile of 83 selected isolates was assessed across a gradient of pH 9 to 14. Growth assays revealed a progressive decline in microbial viability with increasing alkalinity; while all isolates exhibited growth at pH 9, viability remained robust at pH 10 and 11 as well, with 71 and 57 strains surviving, respectively (Figure 3). A pronounced survival threshold was observed at pH 12, where viability decreased to less than 50% (n = 34, 41.0%). Notably, 18 isolates displayed extreme alkalitolerance, maintaining viability at pH 13, although no growth was recorded at pH 14. These 18 hyperalkalitolerant strains were selected for further characterization. Taxonomically, the extreme alkalitolerant group was dominated by the genera Sutcliffiella and Halomonas (n = 3 each). Conversely, the least tolerant subset, those failing to thrive beyond pH 9 or 10, was primarily composed of Enterococcus (n = 5) and Micrococcus (n = 3) species.

3.3. Polyextremophilic profiling of hyper-alkalitolerant strains: Acid, salt, and thermal tolerance

To evaluate polyextremophilic potential, the 18 hyper-alkalitolerant isolates (pre-qualified at pH 13.0) were subjected to cross-stress tolerance across gradients of low pH, high salinity, and elevated temperatures (Table 2).

3.3.1. Acid tolerance spectrum. All 18 isolates demonstrated growth under neutral and mildly alkaline conditions (pH 7.0 and 8.0). However, assays under acidic conditions revealed a gradual decline in survival: 15 isolates maintained viability at pH 6.0, and 14 strains persisted down to pH 5.0, whereas absolute growth arrest occurred for all isolates below pH 5.0.

3.3.2. Halotolerance. Salt tolerance assays across a 2–30% NaCl gradient revealed high adaptability. All isolates demonstrated halotolerance up to 6% NaCl, while 17 strains (excluding Brachybacterium sp. BK118) sustained growth at 8% NaCl; 15 isolates remained viable at 10% NaCl. A significant decline in viability was observed at higher salinities, with only 7 isolates surviving 12% NaCl, 4 strains enduring 20% NaCl, and none capable of surviving the maximum tested concentration of 30% NaCl.

3.3.3. Temperature tolerance. Thermal tolerance profiling (40, 50, and 60 °C) indicated that while all isolates tolerated 40 °C, only six survived at 50 °C, and none exhibited growth at 60 °C.

3.3.4. Polyextremophilic traits. In terms of polyextremophilic capacity, Staphylococcus arlettae LS109 exhibited the most robust phenotype, showing complete tolerance across the maximum tested thresholds (pH 5.0, 20% NaCl, and 50°C). Distinct specialized profiles also emerged: Halomonas sp. BS108 and BK110 combined extreme halotolerance (20% NaCl) with acid tolerance (pH 5.0), whereas a thermotolerant cohort composed of Micrococcus luteus BS121, Exiguobacterium sp. BK112, Cytobacillus kochii BS903, and Brachybacterium sp. BK118 paired thermal endurance (50°C) with acid survival (pH 5.0), highlighting their potential for biotechnological applications in extreme environments.

3.4. Production of alkaline-active extracellular hydrolytic enzymes and bioemulsifiers

3.4.1. Screening and prevalence of alkaline-active biocatalysts. Qualitative screening of the 18 hyper-alkalitolerant isolates across the designated alkaline spectrum (pH 8.0 to 13.0) revealed a widespread capacity for secreting robust, alkaline-active extracellular hydrolases. Extracellular proteolytic activity was exceptionally prevalent, with 14 strains producing clear zones of substrate degradation throughout the entire pH 8.0–13.0 range. Amylolytic activity was also widespread, with 13 isolates exhibiting clear zones of starch hydrolysis from pH 8.0 to 12.0; no amylase activity was detected at pH 13.0, indicating loss of activity under extreme alkalinity. Concurrent production of amylase and protease was common, with 11 strains demonstrating dual enzyme activity under these alkaline conditions. In contrast to the ubiquity of proteases and amylases, cellulolytic activity was uniquely rare. Cellulase production was identified solely in Bacillus sp. BK917, where it exhibited low-level expression characterized by a compact zone of hydrolysis.

To semi‑quantitatively evaluate enzyme secretion across the alkaline pH gradient, clear zone diameters (expressed as relative activity) were measured for amylase (pH 8–12) and protease (pH 8–13) using standard plate assays. For amylolytic activity, the relative activity varied with pH and strain. The highest clear zone values were observed at pH 8–9, with a gradual decline at higher alkalinity. Sutcliffiella horikoshii TP109 exhibited the strongest amylase production at pH 9 (relative activity 17.7), followed by Exiguobacterium sp. BK112 at pH 9 (18.7) and pH 8 (15.5). Most amylase‑positive strains retained detectable activity up to pH 12, albeit at reduced levels (relative activities typically 1.5–2.5). Proteolytic activity, assessed across pH 8–13, showed broader alkaline tolerance. Peak relative activities were generally observed between pH 9 and 11. Kocuria sp. BK904 and Micrococcus luteus DT909 displayed the highest clear zone values at pH 11 (10.33 and 10.73, respectively). Several strains, including Alkalihalophilus pseudofirmus BK103 and Stenotrophomonas maltophilia BK920, maintained substantial proteolytic activity even at pH 13 (relative activities >3.0), underscoring their extreme alkaline stability.

3.4.2. Surface-active properties and bioemulsification capacity. Screening for surface-active traits revealed that bioemulsifier production was restricted to five hyper-alkalitolerant isolates: Halomonas sp. BK110, Sutcliffiella horikoshii BS102, Sutcliffiella horikoshii TP112, Exiguobacterium sp. BK112, and Brachybacterium sp. BK118. Quantitative evaluation of bioemulsification using the 24-h emulsification index (E₂₄) showed variation among the positive isolates. The highest emulsification activity was observed for Halomonas sp. BK110 and Sutcliffiella horikoshii BS102, both of which showed an E₂₄ value of 41.1 ± 1.92%, followed by Sutcliffiella horikoshii TP112 (27.8 ± 1.92%), Exiguobacterium sp. BK112 (26.7 ± 1.67%), and Brachybacterium sp. BK118 (17.8 ± 1.92%).

4. Discussion

The present study systematically characterized the culturable microbial communities inhabiting everyday anthropogenic alkaline formulations. The recovery of 83 distinct bacterial taxa from these environments indicates that such products function as selective, high-pH niches capable of supporting diverse and metabolically versatile alkalitolerant bacteria.

4.1. Anthropogenic alkaline household products as overlooked microbial niches

Natural alkaline environments such as soda lakes, alkaline soils, and serpentinising springs have long been recognised as reservoirs of diverse alkaliphilic and alkalitolerant bacteria [24]. The present study demonstrated that five common household alkaline products – baking soda, bar soap, liquid soap, detergent powder, and talcum powder – consistently harbour viable, culturable alkalitolerant bacteria. The recovery of 100 isolates, which dereplicated to 83 unique 16S rRNA sequence types representing 24 genera, showed that these everyday commodities are not merely transient carriers of microorganisms but constitute stable, selective habitats. Although these products are regularly handled and not sterile, they have remained largely overlooked as microbial niches.

The strong source‑dependence of community composition indicates that product formulation, not only pH, shapes microbial assembly. Baking soda yielded the highest genus richness (15 genera) and the largest number of isolates (32), while the more complex formulated products (soaps, detergent, talc) harboured fewer genera but maintained specialised communities. This pattern suggests that high pH acts as a primary selective filter, but additional chemical components – surfactants, preservatives, low water activity – further constrain community composition. The consistent recovery of viable bacteria from all five products argues against transient contamination; rather, these anthropogenic niches support persistent, adapted populations.

4.2. Dominance of Gram‑positive bacteria and ecological drivers

An overarching feature of the isolate library was the overwhelming dominance of Gram‑positive bacteria, which accounted for 85% of all isolates. Within the Gram‑positive fraction, the phyla Bacillota (57%) and Actinomycetota (27%) were predominant. This strong bias is consistent with the well‑documented resilience of Gram‑positive lineages to alkaline stress, largely attributable to their thick, cross‑linked peptidoglycan cell wall, which provides superior mechanical and osmotic stability compared to the outer membrane‑lipopolysaccharide complex of Gram‑negative bacteria [25,26]. The high prevalence of genera such as Bacillus, Sutcliffiella, Micrococcus, and Staphylococcus further supports this interpretation, as many of these taxa are known for their extreme‑tolerance adaptations, including spore formation, efficient Na⁺/H⁺ antiporters, and secretion of alkaline‑stable enzymes [27,28]. The isolation of obligate alkaliphiles such as Alkalihalophilus pseudofirmus from multiple products confirms that these environments are not merely transient reservoirs but true habitats for specialised extremophiles [29].

4.3. Product-specific niche specialization and source-dependent community structure

The product‑specific community structures point to niche specialisation driven by the unique physicochemical properties of each matrix. Talcum powder, a low‑moisture mineral powder, contained a relatively high proportion of spore‑forming Bacillaceae (e.g., Bacillus, Paenibacillus, Sutcliffiella). Spore formation is a well‑known adaptation to desiccation and nutrient scarcity [30], and our findings suggest that this trait is advantageous in the dry, low‑organic‑matter environment of talc.

Liquid soaps and detergent powders, which are routinely used for cleaning and contain surfactants and preservatives, were dominated by Staphylococcus and Micrococcus. Both genera are known to possess efflux pumps, biofilm‑forming capacities, and enzyme systems that confer resistance to high pH as well as to antimicrobial chemicals commonly found in such formulations [31,32]. Bar soap showed a distinct pattern, with Micrococcus as the most abundant genus (35.7% of its isolates) and a notable absence of Staphylococcus. The solid, intermittently wetted surface of bar soap may select for desiccation‑tolerant Actinobacteria, a group in which Micrococcus is well represented [33,34].

Baking soda stands out as a distinct niche. Its chemically simple composition (sodium bicarbonate) lacks the surfactants, preservatives, and high salt load of formulated products. Consequently, it supported the highest generic diversity and, notably, the highest proportion of Gram‑negative bacteria (21.9% of isolates from baking soda vs. an average of 11.8% in formulated products). This observation strongly suggests that product formulation, not only pH, governs microbial community structure. The bicarbonate ion may also serve as an inorganic carbon source, and its buffering capacity could create micro‑gradients that facilitate niche partitioning [35,36]. The enrichment of Gram‑negative genera such as Klebsiella, Stenotrophomonas, Halomonas, and Brucella in baking soda aligns with this interpretation, as these taxa often possess versatile resistance mechanisms but may be more susceptible to the combined stresses of formulated products [28,37].

4.4. Physiological thresholds and polyextremophilic adaptation to pH, salt, and temperature stress

The pH tolerance screening of 83 isolates revealed a progressive decline in viability with increasing alkalinity: all isolates grew at pH 9, 71 at pH 10, 57 at pH 11, 34 at pH 12, and only 18 at pH 13; none grew at pH 14. The sharp drop between pH 11 and 12 marks a well‑known bioenergetic bottleneck: at very high external pH, the proton‑motive force required for ATP synthesis collapses unless cells possess highly efficient Na⁺/H⁺ antiporters and Na⁺‑coupled ATP synthases [38,39]. The 18 hyper‑alkalitolerant strains belonged to phylogenetically diverse genera (Alkalihalophilus, Halomonas, Sutcliffiella, Kocuria, Exiguobacterium etc.), indicating that extreme alkaline tolerance is a convergent functional trait rather than a lineage‑specific property – a pattern also observed in soda lake microbiomes [40].

When subjected to cross‑stress assays, these 18 isolates displayed moderate acid tolerance (most survived pH 5.0 but not pH 4.0), halotolerance up to 10% NaCl (with a few reaching 20%), and thermal tolerance up to 50 °C (but none at 60 °C). This polyextremophilic capacity is consistent with their ecological niches: household products are not only alkaline but also periodically dried, contain salts, and may experience temperature fluctuations during storage. Notably, Staphylococcus arlettae LS109 exhibited the most robust multi‑stress phenotype (tolerance to pH 5.0, 20% NaCl, and 50 °C), while Halomonas sp. BS108 and BK110 combined extreme halotolerance (20% NaCl) with acid tolerance. These strains represent valuable models for studying the molecular basis of stress cross‑protection in synthetic alkaline environments.

4.5. Functional versatility of alkaline-active hydrolases and surface-active compounds

Qualitative screening of the 18 hyper‑alkalitolerant isolates revealed widespread extracellular enzyme production under alkaline conditions (pH 8–13). Proteolytic activity was the most prevalent (14 isolates active up to pH 13), followed by amylolytic activity (13 isolates, but activity absent at pH 13). The broader alkaline stability of proteases compared to amylases is consistent with literature reports: many bacterial alkaline proteases retain activity up to pH 12–13 due to structural features such as increased negative surface charge and salt bridge networks, whereas amylases typically denature above pH 12 [41,42]. Concurrent production of both enzymes by 11 isolates suggests that multi‑enzyme secretion is a common adaptation in these anthropogenic niches.

Cellulolytic activity was exceptionally rare, detected only in Bacillus sp. BK917, albeit with low activity. This narrow distribution may reflect the absence of cellulosic substrates in household products, leading to loss or downregulation of cellulase genes. Bioemulsifier production was restricted to five isolates, with the highest emulsification indices (E₂₄ = 41.1%) observed for Halomonas sp. BK110 and Sutcliffiella horikoshii BS102. These surface‑active compounds likely aid in survival by modifying interfacial properties in surfactant‑rich environments, and their presence in multiple genera suggests that emulsification is an underappreciated functional trait in alkaline consumer product microbiomes. Bacillus sp. BK917 distinguished itself as the most functionally versatile strain, combining amylase, protease, cellulase, and bioemulsifier activities, making it a prime candidate for follow‑up genomic and bioprospecting studies.

4.6. Ecological links to natural alkaliphilic genera and polyextremophilic adaptation

Many of the genera identified in this study (Bacillus, Micrococcus, Staphylococcus, Exiguobacterium, Halomonas, Alkalihalophilus) are known from natural alkaline or saline‑alkaline environments such as soda lakes, alkaline hot springs, and carbonate‑rich soils. For example, Alkalihalophilus pseudofirmus is a model organism for studying Na⁺/H⁺ antiport and cell‑wall adaptations to high pH [25]. Halomonas species are widespread in hypersaline and alkaline lakes. The recovery of such genera from household products indicates that these synthetic matrices functionally resemble natural alkaline habitats in their selective pressure. Furthermore, several isolates exhibited polyextremophilic traits (combined alkali, salt, and moderate temperature tolerance), a property that is ecologically advantageous in fluctuating natural environments and also highly desirable for industrial biocatalysis. The polyextremophilic nature of strains such as S. arlettae LS109 and Halomonas sp. BS108 points to the potential for discovering novel stress‑tolerant enzymes and metabolites through further characterisation.

4.7. Limitations of the study

We acknowledge several limitations. First, all isolations were performed using standard enrichment on Horikoshi‑I and R2A media at pH 9–10; therefore, we recovered only the culturable fraction that grows under those specific conditions. Fastidious or obligately anaerobic alkaliphiles would have been missed. Second, although we monitored pH stability after autoclaving and during growth, we did not use buffered media (e.g., carbonate‑bicarbonate or CAPS buffers) to maintain constant pH throughout the assay period. Small pH drifts cannot be entirely excluded, although the consistent growth patterns across replicates argue against major fluctuations. Third, despite strict aseptic technique, the isolation of human‑associated genera (Staphylococcus, Enterococcus, Klebsiella) raises the possibility of occasional cross‑contamination from skin or airborne sources. However, the clear product‑specific distribution patterns (e.g., absence of Staphylococcus from bar soap and its high abundance in liquid soap) suggest that genuine colonization, rather than contamination, is the dominant phenomenon. Fourth, 16S rRNA gene sequencing provides genus‑level identification but limited resolution at the species or strain level; whole‑genome sequencing would be required to confirm species assignments and to uncover functional gene repertoires.

4.8. Future perspectives

The present study opens several avenues for future research. Whole‑genome sequencing of the most polyextremophilic and enzyme‑rich isolates (e.g., Bacillus sp. BK917, Halomonas sp. BK110, S. arlettae LS109) could reveal the genetic determinants underlying their tolerance to multiple stresses and their broad hydrolytic capacity. Genome analysis and comparative genomics, in particular, has proven powerful for identifying stress‑response pathways and secretory systems in related alkalitolerant bacteria [43]. Such analyses would also help determine whether the same adaptive modules recur across phylogenetically distinct isolates from these anthropogenic niches.

Metagenomic analysis of the product microbiomes might uncover unculturable taxa and functional gene clusters, including those involved in the biosynthesis of exopolysaccharides (EPS), siderophores, compatible solutes, and other secondary metabolites. EPS production is a key strategy for biofilm formation, desiccation resistance, and overall microbial persistence in diverse environments and has been associated with a range of bioactive functions [44,45]. Siderophores facilitate iron acquisition under nutrient‑limited conditions, thereby enhancing competitiveness in resource‑scarce matrices [46]. Compatible solutes play a crucial role in osmotic adjustment and stabilisation of cellular structures under stress conditions, including high salinity and desiccation [47]. Parallel screening for antimicrobial compounds is equally warranted, as competitive microbial interactions in these resource‑limited, high‑pH environments may select for the production of novel bioactive metabolites [48]. Investigating whether these isolates co‑produce multiple stress‑linked extracellular products – enzymes, EPS, siderophores, compatible solutes, antimicrobials, and bioemulsifiers – would provide a holistic view of their ecological adaptation.

From an applied perspective, the alkaline‑active proteases, amylases, and bioemulsifiers reported here deserve purification, characterisation, and testing in industrial formulations (e.g., detergents, textile processing, bioremediation of alkaline wastes). The combination of genome‑mining, functional assays, and targeted metabolite analysis will transform this culture collection into a valuable resource for both basic extremophile ecology and industrial biotechnology.

4.9. Concluding remarks

This study demonstrates that everyday alkaline household products – often considered purely chemical or hygienic items – are in fact functional anthropogenic niches that harbour diverse, ecophysiologically adaptable alkalitolerant bacteria. Product formulation, not only pH, is a major determinant of community composition, with baking soda supporting the highest diversity and the greatest enrichment of Gram‑negative taxa. The robust polyextremophilic nature of several isolates, together with their production of alkaline‑active hydrolases, bioemulsifiers, and potentially other bioactive metabolites (e.g., exopolysaccharides and antimicrobials), positions this bacterial collection as a promising resource for biotechnological exploration and for understanding microbial life in man‑made extreme environments.

Declarations and Info

Acknowledgments

The authors thank the members of the HOPE Lab for their support throughout this project. Investigating a previously overlooked alkaline niche, TJH gratefully acknowledges the legacy of the late Professor Koki Horikoshi, whose pioneering work continues to inspire this research. He also extends sincere thanks to Professor Suzuki for his mentorship during doctoral training, which fostered his enduring interest in microbial biochemistry, and to Professor Masahiro Ito for influential insights into alkaliphile biology that inspired this work.

Author Contributions

TJH conceived the project. MKU and TJH contributed to fund acquisition and administrative managements. JS, IHN, AKAR, MSK, SH, IKF, SAZ, MNAC and TJH conducted the experiments. MSB and IHN performed the sequence and taxonomic analyses. TJH, IHN and JS were involved in data interpretation. FA provided technical advice during the study. TJH, TR and IHN wrote and prepared the manuscript. All authors approved the manuscript.

Funding

This study was supported by grants from the Ministry of Science and Technology, Government of the People's Republic of Bangladesh.

Conflict of Interest

The authors declare no conflicts of interest.

Ethical Approval

This study did not involve human or animal subjects.

References

[1] M. Rawat, M. Chauhan, A. Pandey, Extremophiles and their expanding biotechnological applications, Arch. Microbiol. 206 (2024) 247. https://doi.org/10.1007/s00203-024-03981-x.

[2] P.P. Kanekar, S.P. Kanekar, Alkaliphilic, Alkalitolerant Microorganisms, in: P.P. Kanekar, S.P. Kanekar (Eds.), Divers. Biotechnol. Extrem. Microorg. India, Springer Nature, Singapore, 2022: pp. 71–116. https://doi.org/10.1007/978-981-19-1573-4_3.

[3] M. Haines, V. Khot, M. Strous, The Vigor, Futility, and Application of Microbial Element Cycles in Alkaline Soda Lakes, Elements 19 (2023) 30–36. https://doi.org/10.2138/gselements.19.1.30.

[4] D. Li, Z. Qi, J. Guo, T. Wang, X. Li, N. Hou, Study on the screening of high-efficiency salt and alkali-tolerant microbial agents and their roles and mechanisms in enhancing saline-alkaline soil remediation, J. Clean. Prod. 519 (2025) 145992. https://doi.org/10.1016/j.jclepro.2025.145992.

[5] A.S. Rao, A. Nair, K. Nivetha, V.S. More, K.S. Anantharaju, S.S. More, Chapter 7 - Molecular adaptations in proteins and enzymes produced by extremophilic microorganisms, in: N.K. Arora, S. Agnihotri, J. Mishra (Eds.), Extrem. Their Ind. Appl., Academic Press, 2022: pp. 205–230. https://doi.org/10.1016/B978-0-323-90274-8.00002-2.

[6] M. Saritha, P. Kumar, N.R. Panwar, U. Burman, Physiological and Metabolic Basis of Microbial Adaptations Under Extreme Environments, in: Extreme Environ., CRC Press, 2021.

[7] A.K. Wani, N. Akhtar, F. Sher, A.A. Navarrete, J.H.P. Américo-Pinheiro, Microbial adaptation to different environmental conditions: molecular perspective of evolved genetic and cellular systems, Arch. Microbiol. 204 (2022) 144. https://doi.org/10.1007/s00203-022-02757-5.

[8] M.K. Gustav, S. Peter, A.N. Newlove, A.M. Elhadi Sulieman, Chapter 24 - Microbial enzymes with special characteristics for biotechnological applications, in: A.M.E. Sulieman (Ed.), Microb. Enzym., Academic Press, 2026: pp. 361–387. https://doi.org/10.1016/B978-0-443-40352-1.00024-6.

[9] N. Sarwa, P. Kumari, D. Meena, P. Udawat, N.S. Chaudhary, Alkaline Proteases from Haloalkaliphiles: Unveiling Nature's Catalysts for Diverse Applications, Appl. Biochem. Microbiol. 60 (2024) 855–870. https://doi.org/10.1134/S0003683824603676.

[10] G.K. Gupta, M. Dixit, R.K. Kapoor, P. Shukla, Xylanolytic Enzymes in Pulp and Paper Industry: New Technologies and Perspectives, Mol. Biotechnol. 64 (2022) 130–143. https://doi.org/10.1007/s12033-021-00396-7.

[11] F. Azeem, A. Sumrin, T. Malik, M. Shaheen, N. Hussain, Microbial Enzymes in Textile Bioprocessing, in: M. Khurshid, M.A. Mehmood, M. Kashif (Eds.), Microb. Biotechnol. Text. Innov., Springer Nature, Singapore, 2025: pp. 27–47. https://doi.org/10.1007/978-981-95-0347-6_2.

[12] W. Xi, Y. Ping, M.A. Alikhani, A Review on Biosurfactant Applications in the Petroleum Industry, Int. J. Chem. Eng. 2021 (2021) 5477185. https://doi.org/10.1155/2021/5477185.

[13] M. Zobaer, F. Ali, M.N. Anwar, M.S.H. Bappi, T.J. Hossain, Glycolipid-and Peptidoglycolipid-Like Biosurfactants from Pseudomonas spp.: Preliminary Characterization of Stability, Emulsification, and Antimicrobial Activity, Prelim. Charact. Stab. Emuls. Antimicrob. Act. July 23 2025 (2025). https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5362789 (accessed March 6, 2026).

[14] S. Varshney, A. Bhattacharya, A. Gupta, Halo-alkaliphilic microbes as an effective tool for heavy metal pollution abatement and resource recovery: challenges and future prospects, 3 Biotech 13 (2023) 400. https://doi.org/10.1007/s13205-023-03807-5.

[15] Z. Ma, S. Song, Y. Han, The screening and optimization of agricultural microbial strains based on artificial intelligence: Application status, challenges, and prospects in the field of salt-alkali-tolerant crops, Adv. Resour. Res. 5 (2025) 2005–2020. https://doi.org/10.50908/arr.5.4_2005.

[16] J. Arora, A. Kumari, A. Ranjan, V.D. Rajput, S. Shende, E.V. Prazdnova, S.S. Mandzhieva, S. Sushkova, T. Minkina, A. Chauhan, R. Srivastav, T. Jindal, Microbial Adaptation in Different Extreme Environmental Conditions and Its Usefulness in Differently Polluted Soil, in: A. Ranjan, V.D. Rajput, A. Chauhan, E.V. Prazdnova, T. Minkina, S.M. Zargar (Eds.), Extrem. Sustain. Agric. Soil Health Improv., Springer Nature Switzerland, Cham, 2024: pp. 47–62. https://doi.org/10.1007/978-3-031-70203-7_3.

[17] A. Naykodi, S.C. Patankar, B.N. Thorat, Alkaliphiles for comprehensive utilization of red mud (bauxite residue)---an alkaline waste from the alumina refinery, Environ. Sci. Pollut. Res. 30 (2023) 9350–9368. https://doi.org/10.1007/s11356-022-24190-3.

[18] R.M. Jain, K. Mody, A. Mishra, B. Jha, Isolation and structural characterization of biosurfactant produced by an alkaliphilic bacterium Cronobacter sakazakii isolated from oil contaminated wastewater, Carbohydr. Polym. 87 (2012) 2320–2326.

[19] F. Sessa, E. Panepinto, M. Salerno, M. Chisari, M. Esposito, G. Cocimano, C. Pomara, Impact of liquid antibacterial soap and hand sanitizer on DNA transfer in forensic investigations: an experimental study, Forensic Sci. Res. 10 (2025) owae068. https://doi.org/10.1093/fsr/owae068.

[20] T.J. Hossain, S.I. Chowdhury, H.A. Mozumder, M.N.A. Chowdhury, F. Ali, N. Rahman, S. Dey, Hydrolytic Exoenzymes Produced by Bacteria Isolated and Identified From the Gastrointestinal Tract of Bombay Duck, Front. Microbiol. 11 (2020). https://doi.org/10.3389/fmicb.2020.02097.

[21] M. Uddin, S. Lima, T.J. Hossain, N. Kar, Y. Zahan, B. Olarewaju Abdulkareem, Evaluation of cellulolytic endo-1,4-β-d-glucanase activity in the digestive fluid of adult phytophagous beetle Hoplasoma unicolor, Trop. Life Sci. Res. 32 (2021) 53–68. https://doi.org/10.21315/tlsr2021.32.3.4.

[22] M. Zobaer, F. Ali, M.N. Anwar, M.S.H. Bappi, T.B. Bakar, T.J. Hossain, Isolation of Biosurfactant Producing Bacteria from Oil-Spilled Soil and Characterization of Their Secreted Biosurfactants in Pathogen-Inhibition and Oil-Emulsification, Int J Pharm Sci Res 15 (2024) 1174–83. https://doi.org/10.13040/IJPSR.0975-8232.15(4).1174-83.

[23] F. Ali, S. Das, T.J. Hossain, S.I. Chowdhury, S.A. Zedny, T. Das, M.N.A. Chowdhury, M.S. Uddin, Production optimization, stability and oil emulsifying potential of biosurfactants from selected bacteria isolated from oil-contaminated sites, R. Soc. Open Sci. 8 (2021) 211003. https://doi.org/10.1098/rsos.211003.

[24] S.L. Smith, A. Rizoulis, J.M. West, J.R. Lloyd, The Microbial Ecology of a Hyper-Alkaline Spring, and Impacts of an Alkali-Tolerant Community During Sandstone Batch and Column Experiments Representative of a Geological Disposal Facility for Intermediate-Level Radioactive Waste, Geomicrobiol. J. 33 (2016) 455–467. https://doi.org/10.1080/01490451.2015.1049677.

[25] B. Janto, A. Ahmed, M. Ito, J. Liu, D.B. Hicks, S. Pagni, O.J. Fackelmayer, T.-A. Smith, J. Earl, L.D.H. Elbourne, K. Hassan, I.T. Paulsen, A.-B. Kolstø, N.J. Tourasse, G.D. Ehrlich, R. Boissy, D.M. Ivey, G. Li, Y. Xue, Y. Ma, F.Z. Hu, T.A. Krulwich, Genome of alkaliphilic Bacillus pseudofirmus OF4 reveals adaptations that support the ability to grow in an external pH range from 7.5 to 11.4, Environ. Microbiol. 13 (2011) 3289–3309. https://doi.org/10.1111/j.1462-2920.2011.02591.x.

[26] M. Rohde, The Gram-Positive Bacterial Cell Wall, Microbiol. Spectr. 7 (2019) 10.1128/microbiolspec.gpp3-0044–2018. https://doi.org/10.1128/microbiolspec.gpp3-0044-2018.

[27] Y. Atakav, E. Kurpejović, D. Kazan, N.A. Sayar, An Exploratory Study on the Growth Dynamics of Alkalihalophilus marmarensis Using a Model-Based Approach, Appl. Microbiol. 5 (2025) 69. https://doi.org/10.3390/applmicrobiol5030069.

[28] E. Padan, E. Bibi, M. Ito, T.A. Krulwich, Alkaline pH homeostasis in bacteria: New insights, Biochim. Biophys. Acta BBA - Biomembr. 1717 (2005) 67–88. https://doi.org/10.1016/j.bbamem.2005.09.010.

[29] Y. Wei, T.W. Southworth, H. Kloster, M. Ito, A.A. Guffanti, A. Moir, T.A. Krulwich, Mutational loss of a K+ and NH4+ transporter affects the growth and endospore formation of alkaliphilic Bacillus pseudofirmus OF4, J. Bacteriol. 185 (2003) 5133–5147. https://doi.org/10.1128/JB.185.17.5133-5147.2003.

[30] W.L. Nicholson, N. Munakata, G. Horneck, H.J. Melosh, P. Setlow, Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments, Microbiol. Mol. Biol. Rev. MMBR 64 (2000) 548–572. https://doi.org/10.1128/MMBR.64.3.548-572.2000.

[31] A. Dashtbani-Roozbehani, M.H. Brown, Efflux Pump Mediated Antimicrobial Resistance by Staphylococci in Health-Related Environments: Challenges and the Quest for Inhibition, Antibiotics 10 (2021) 1502. https://doi.org/10.3390/antibiotics10121502.

[32] A. Nostro, L. Cellini, M. Di Giulio, M. D'Arrigo, A. Marino, A.R. Blanco, A. Favaloro, G. Cutroneo, G. Bisignano, Effect of alkaline pH on staphylococcal biofilm formation, APMIS Acta Pathol. Microbiol. Immunol. Scand. 120 (2012) 733–742. https://doi.org/10.1111/j.1600-0463.2012.02900.x.

[33] F. Mohammadipanah, J. Wink, Actinobacteria from Arid and Desert Habitats: Diversity and Biological Activity, Front. Microbiol. 6 (2016). https://doi.org/10.3389/fmicb.2015.01541.

[34] F. Xie, W. Pathom-aree, Actinobacteria From Desert: Diversity and Biotechnological Applications, Front. Microbiol. 12 (2021). https://doi.org/10.3389/fmicb.2021.765531.

[35] A.G. Delgado, P. Parameswaran, D. Fajardo-Williams, R.U. Halden, R. Krajmalnik-Brown, Role of bicarbonate as a pH buffer and electron sink in microbial dechlorination of chloroethenes, Microb. Cell Factories 11 (2012) 128. https://doi.org/10.1186/1475-2859-11-128.

[36] K. Mokashi, V. Shetty, S.A. George, G. Sibi, Sodium Bicarbonate as Inorganic Carbon Source for Higher Biomass and Lipid Production Integrated Carbon Capture in Chlorella vulgaris, Achiev. Life Sci. 10 (2016) 111–117. https://doi.org/10.1016/j.als.2016.05.011.

[37] Yu.V. Boltyanskaya, A.N. Antipov, T.V. Kolganova, A.M. Lysenko, N.A. Kostrikina, T.N. Zhilina, Halomonas campisalis, an Obligatorily Alkaliphilic, Nitrous Oxide–Reducing Denitrifier with a Molybdenum Cofactor–Lacking Nitrate Reductase, Microbiology 73 (2004) 271–278. https://doi.org/10.1023/B:MICI.0000032236.51403.58.

[38] D.B. Hicks, J. Liu, M. Fujisawa, T.A. Krulwich, F1F0-ATP synthases of alkaliphilic bacteria: lessons from their adaptations, Biochim. Biophys. Acta 1797 (2010) 1362–1377. https://doi.org/10.1016/j.bbabio.2010.02.028.

[39] L. Preiss, D.B. Hicks, S. Suzuki, T. Meier, T.A. Krulwich, Alkaliphilic Bacteria with Impact on Industrial Applications, Concepts of Early Life Forms, and Bioenergetics of ATP Synthesis, Front. Bioeng. Biotechnol. 3 (2015) 75. https://doi.org/10.3389/fbioe.2015.00075.

[40] C.D. Vavourakis, A.-S. Andrei, M. Mehrshad, R. Ghai, D.Y. Sorokin, G. Muyzer, A metagenomics roadmap to the uncultured genome diversity in hypersaline soda lake sediments, Microbiome 6 (2018) 168. https://doi.org/10.1186/s40168-018-0548-7.

[41] A. Hemsinli, S. Gurkok, Evaluation of a novel purified and characterized alkaline protease from the extremophile Exiguobacterium alkaliphilum VLP1 as a detergent additive, Biotechnol. J. 19 (2024) e2300441. https://doi.org/10.1002/biot.202300441.

[42] Z. Li, Y. Xing, P. Liu, W. Liao, L. Miao, Redox and solvent-stable alkaline serine protease from Bacillus patagoniensis DB-5: heterologous expression, properties, and biotechnological applications, Front. Microbiol. 16 (2025). https://doi.org/10.3389/fmicb.2025.1558419.

[43] T.J. Hossain, Functional genomics of the lactic acid bacterium Limosilactobacillus fermentum LAB-1: metabolic, probiotic and biotechnological perspectives, Heliyon 8 (2022). https://doi.org/10.1016/j.heliyon.2022.e11412.

[44] N. Tarannum, F. Ali, M.S. Khan, O.S. Alhumaidan, A.N.M.S. Zawad, T.J. Hossain, Bioactive exopolysaccharide from Limosilactobacillus fermentum LAB-1: Antioxidant, anti-inflammatory, antibacterial and antibiofilm properties, Bioact. Carbohydr. Diet. Fibre 31 (2024) 100409. https://doi.org/10.1016/j.bcdf.2024.100409.

[45] N. Tarannum, T.J. Hossain, F. Ali, T. Das, K. Dhar, I.H. Nafiz, Antioxidant, antimicrobial and emulsification properties of exopolysaccharides from lactic acid bacteria of bovine milk: Insights from biochemical and genomic analysis, LWT 186 (2023) 115263. https://doi.org/10.1016/j.lwt.2023.115263.

[46] T.J. Hossain, Genome analysis of Pantoea dispersa PGPR-24 reveals key genetic pathways for plant growth promotion, root colonization and nutrient mobilization, Preprint (2024).

[47] S.H. Wani, N.B. Singh, A. Haribhushan, J.I. Mir, Compatible Solute Engineering in Plants for Abiotic Stress Tolerance - Role of Glycine Betaine, Curr. Genomics 14 (2013) 157–165. https://doi.org/10.2174/1389202911314030001.

[48] T.J. Hossain, Methods for screening and evaluation of antimicrobial activity: A review of protocols, advantages, and limitations, Eur. J. Microbiol. Immunol. 14 (2024) 97–115. https://doi.org/10.1556/1886.2024.00035.

Download PDF Full Text

ResearchGate Preprint

Tags

Alkalitolerant bacteria · Anthropogenic alkaline niches · Alkaliphilic bacteria · Extreme pH tolerance · Alkaline-active hydrolases · Alkaline amylase · Alkaline protease · Consumer-product microbiome · Household cleaning products · Stress physiology

Citation of Preprint

Nafiz, I. H., Sultana, J., Akhter, K., Khan, M. S., Hasan, S., Bappi, M. S. H., Rahman, T., Faisal, I. K., Chowdhury, M. N. A., Zedny, S. A., Ali, F., Uddin, M. K., & Hossain, T. J. (2025). Anthropogenic Alkaline Niches as a Habitat for Alkalitolerant Bacteria: Taxonomy, Ecophysiology, and Biotechnologically Relevant Hydrolases. Preprint.

Explore More Research from HOPE Lab

View all Preprints

Browse our Peer‑Reviewed Publications