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Nitrogen cycle: nitrification, archaea, N2O emission, comammox
Nitrogen cycle: nitrification, archaea, N2O emission, comammox
Archaea are cosmopolitan members in planktonic prokaryotes in oceans and terrestrial environments. Several groups of planktonic Archaea were discovered in oceanic provinces: Thaumarchaeotal (Marine Group (MG) I and IA), Euryarchaeal (MGII, III, and IV). The only archaea cultivated in the laboratories were Marine Group I which was suggested as ammonia oxidizers. The first step of nitrification, oxidation of ammonia, long thought to be exclusive to the domain Bacteria, was recently tied to the archaeal domain. However, the contribution of AOA to nitrification in soil is still controversial. To date, only a limited number of AOA have been isolated and/or enriched in laboratory culture. This narrow field of characterized AOA has impaired our ability to advance our understanding of AOA in soil environments. We have cultures of ammonia-oxidizing archaea and are characterizing ecophysiology of them using metagenomics approaches to find factors affecting nitrification in oceans and terrestrial environments. Nitrification is a key process affecting N2O emission and eutrophication. Many interesting features of nitrogen cycles are hidden and those are related to sustainable management of environments of Earth.
Methane cycle: metabolic versatility of methanotrophs
Methane cycle: metabolic versatility of methanotrophs
Anthropogenic emissions of greenhouse gases (GHGs)—primarily carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—are responsible for a historically rapid increase in Earth's average annual temperature of more than 0.2°C per decade. GHG production and consumption in both natural and anthropogenic ecosystems are driven primarily by microbes. Methane fluxes in natural environments are controlled by activities of methane-producing (methanogenic) and methane-consuming (methanotrophic) microorganisms. It is estimated that 69% of the atmospheric CH4 budget originates from microbial activities (methanogenesis) while about 50-90% of the produced CH4 is oxidized by methanotrophs before reaching the atmosphere. Aerobic methanotrophs oxidize methane to methanol by employing either particulate methane monooxygenases (pMMO) or soluble methane monooxygenases (sMMO). It has been assumed that methanotrophs has very limited capacity in utilizing electron donor and acceptors. We have been reporting several interesting metabolic properties of methanotrophs previously unknown, which may affect methane cycles in environments. Further using these strains, we can manage to control N2O and CH4 emissions from environments and develop processes for biodegradable plastic production in industries.
Others
Others
Contaminants of oil spill sites move to and stay in anoxic environments. Under anoxic conditions, activation reactions with oxygen are simply not possible and the pollutants frequently become recalcitrant. The anaerobic degradation pathway for a distinct compound is completely different from the respective aerobic degradation pathway due to absence of oxygen and many steps of anaerobic degradation should be bypassed under anoxic conditions. Many electron acceptors including nitrate, sulphate, iron, and bicarbonate could be used for anaerobic degradation. Due to difficulties to access to and understand anaerobic microbial world, many anaerobic microorganisms remained uncovered and the novel biochemical reactions has been frequently found to be involved. To understand anaerobic microbial processes of degradation of aromatic degradation, various technologies such as stable isotope probing, genome amplification, and next generation sequencing were employed. Currently, we are going to analyse diesel and gasoline-degrading microbial consortia under nitrate-/sulfate-/iron-reducing conditions.
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