Cyclotella atomus has a flat valve face with short striae arranged around the margin on the valve. A fultoportula can be seen toward the center of the valve (but slightly off center) appearing as a dark dot. Marginal fultoportulae occur on every fourth to fifth costa and can be seen in deep focus as dark spots.
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Cyclotella atomus from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:
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The small, heteropolar valves are 8-19 m in length by 5-8 m in width. The headpole is broadly rounded while the footpole is cuneately rounded. The fibulae are broad and short with 8-10 in 10 m. The costae and central line are not visible in the LM.
The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Surirella atomus from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:
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Diatomaceous earth or diatomite is a fossil rock deposit of diatoms made up of silica and other minerals. A distinguishing feature of diatoms that placed them in the single class of microalgae Bacillariophyceae, is the frustule, a transparent, hard-shelled cell wall. It's interesting to note that the diatom has specific proteins and enzymes for heavy metal detoxification and can intake and store more heavy metals in its frustule. Consequently, an attempt has been made in this study to determine the bioaccumulation of metals in the frustules of the diatom. Hence, a centric diatom was isolated from the freshwater sample collected from the Adyar River, Chennai, Tamil Nadu. The diameter of the cell was 5-7.5 m and 20-23 striations with radial arrangement. A single, dark off-center fultoportula and marginal fultoportula on the striae are found in the diatom. Additionally, one rimoportula between two marginal fultoportula distributed on the striae between the costa was also seen. As a result, the isolated diatom was morphologically identified as Cyclotella atomus Hust. Simultaneously, the bioaccumulation study reveals that the Titanium (Ti) was found accumulated in the frustules of the diatom incubated in the Ti-supplemented culture medium based on the scanning electron microscope-energy-dispersive X-ray analysis (SEM-EDAX). Therefore, the biogenic accumulation and fabrication of Titanium frustules in diatom have advantages in enhancing the efficiency of solar cells.
Cyclotella atomus grows well at 15-20C and occurs at maximum abundance at the upper end of this range, although it can also tolerate higher temperatures. It has been recorded in the Great Lakes drainage in spring and summer (Klarer and Millie 1994, Poulickova 1993, Stoermer and Ladewski 1976).
Cyclotella atomus can tolerate turbulence as well as frequent osmotic stress. It has been recorded from fresh, brackish, and saltwater. In Lake Michigan, it occurs in littoral areas that have abnormally high chloride levels. It has made up 8.3% of the diatoms in the Lake Ontario and Oswego River regions during periods of high chloride concentration (Hakansson and Clarke 1997, Makarewicz 1987, Mills et al. 1993, Stoermer and Yang 1969, Tanimura et al. 2004).
Copyright: 2013 von Alvensleben et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded through the Advanced Manufacturing Cooperative Research Centre, Melbourne, Australia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
The depletion of fossil energy stores, climate change-associated increasing atmospheric levels of carbon dioxide and freshwater pollution have generated a renewed interest in industrial-scale microalgal biomass production [1]. Industrial algal biomass production can utilize and sequester significant amounts of atmospheric or flue gas carbon dioxide [2] and remove pollutant nutrients such as nitrates, nitrites and phosphates from waste water ponds [3].
Industry aims for microalgae cultivation at various power-stations in Australia for CO2 and NOx remediation from flue gas with parallel production of value-adding biochemicals. However, these sites differ in the water quality for cultivation. A cosmopolitan marine microalga, Nannochloris atomus Butcher (Chlorophyta, synonym for Picochlorum atomus (Butcher) Henley [4]), has a suitable lipid and protein content for aquaculture [5], [6], high biomass production and a potentially broad tolerance to variations of salinity [7], [8]. However, the influence of salinity on growth patterns, nutrient requirements and biochemical profiles below 36 ppt, which are commonly encountered at potential production sites, have to date not been determined. Establishing species-specific growth parameters will identify optimal inoculation cell numbers and culture durations for achieving highest biomass productivity in the shortest possible timeframe. Understanding species-specific daily nutritional requirements will ensure minimal environmental impact (e.g. eutrophication through discharge of nutrient-rich harvest water effluent [9]), whilst also minimising expenses associated with fertilisation.
Nitrogen and phosphorus availability also influences cellular protein, carbohydrate, and lipid content, as well as fatty acid profiles [13], [14]. Nitrogen limitation reduces the synthesis of chloroplastic proteins and chl a, but increases carotenoid content [15] while the surplus of carbon metabolites are stored as storage lipids and - carbohydrates [13], [16]. Higher lipid yields through nitrogen limitation have been obtained for several microalgal species [13], [17], [18] suggesting that target bio-product yields can be optimised through manipulation of culture nutrient status.
Microalgal culture contamination by rogue organisms is an ever-present risk in aquaculture industries [19]. Common contaminants include bacteria, viruses, fungi, other algae and zooplankton (e.g. ciliates, copepods, rotifers) [20]. Current procedures to minimise culture contamination include pH or salinity manipulations [19], [20], the use of ammonium as a nitrogen source, or quinine treatment to reduce amoeba populations [20], [21]. Other remedies, such as the addition of antibiotics [22] carry the risk of antibiotic resistance, placing restrictions on the use of the biomass and waste water disposal.
Culture contamination by non-target algae or cyanobacteria generally results in resource competition [23] and/or the release of potentially toxic allelochemicals into the culture medium, inhibiting growth or killing the target species [24]. This often leads to lost productivity associated with disposal of contaminated cultures, sterilisation, re-inoculation and culture re-establishment. Adverse impacts on product quality can further negatively affect industry, even if productivity is unaffected.
Pseudanabaena limnetica (Lemmermann) Komrek is a filamentous, non-heterocystous [25] and non-toxic [26] freshwater cyanobacterium [27], with a certain degree of halotolerance [28] and is a frequent local nuisance contaminant in outdoor microalgal cultures during the tropical wet season. Consequently, methods must be developed to control levels of contamination, ideally not affecting the target species or influencing final products.
Given the potential importance of P. atomus in aquaculture, this study firstly aimed to determine the influence of salinity on growth, nutrient utilisation, biomass and lipid production and effects of nutrient limitation on biochemical profiles to determine end-product choice and industrial-scale cultivation protocols. Additionally, the effectiveness of salinity manipulations for contamination control of the freshwater cyanobacterial contaminant P. limnetica was investigated.
It is shown that salinity had no effect on P. atomus growth and nutrient utilisation (except at 11 ppt for the latter) and had only a marginal effect on total lipid at 2 ppt and carbohydrate at 8 ppt, respectively, under nutrient-replete conditions. Nutrient status, however, significantly affected total lipid and fatty acid profiles, carbohydrate and protein contents. It is further shown that salinity can be used to control the establishment of P. limnetica.
Growth of Picochlorum atomus was determined daily using turbidity, from triplicate 250 l samples per culture for 20 days and obtained data were transformed to cell numbers and dry weights as described above. Specific growth rates [], (eq. 1) were calculated from culture cell numbers [31], as were the derived parameters divisions per day and generation time [days]. Biomass productivies were determined using equation 2 (modified from Su et al. [32]).
Total carbohydrate content was determined using the phenol-sulphuric acid assay [39]. Prior to analysis, lyophilised algal samples were lysed in MilliQ-purified water with a Bullet Blender bead beater (ZrO2 beads, 0.5 mm diameter) (Next Advance, Lomb Scientific) to enable collection of a homogenous sub-sample for extraction.
Irrespective of salinity, Picochlorum atomus exhibited growth patterns typical of aerated batch cultures [11]. The data established that P. atomus is a euryhaline microalga tolerating freshwater to marine salinities without adverse effects on growth and biomass productivities.
The decrease in growth rate during phases II and III (Fig. 1, Table 1) is characteristic of batch cultures [11] and is generally the consequence of individual or combined effects of culture self-shading, nutrient limitation [45] and microalgal/bacterial exudate accumulation [24], [46]. Initially, these factors are unlikely to have a considerable effect on culture development, particularly considering the low inoculation densities, adequate nutrient provision and low bacteria cultures used in this study. However, over culture time, the accumulation of algal exudates followed by increased self-shading and bacterial growth-inhibiting exudates (negative allelopathic interactions) are likely to cause the observed decreasing growth rates. Nutrient limitation is unlikely to have affected growth as cultures were maintained nutrient-replete with high nitrite levels (Fig. 3), indicating cellular nitrogen stores were filled throughout most of the cultivation period [33]. Additionally, culture re-fertilisation on day 5 had no impact on culture growth; also implying cultures were not nutrient limited. 152ee80cbc
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