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Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future
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Novel processes in microbial nitrogen cycle: methane-driven nitrate reduction and oxygenic denitrification
Monday 7th @ 0950-1010, Multifunction Hall
Baoli Zhu* , Helmholtz Zentrum Muenchen, German research center for environmental health
Presenter Email: baoli.zhu@helmholtz-muenchen.de |
| Microbial nitrogen cycling has been intensively investigated for over a century and was thought to be rather well understood. Yet recent discoveries of novel processes and microbes involved in the nitrogen cycle, e.g., methane-dependent nitrite- and nitrate-reduction, complete ammonia oxidation to nitrate (comammox), have demonstrated that our understanding of microbial nitrogen cycling may be far from complete. Here I would like to discuss two projects that we have been doing in the last few years, revealing novel microbes and microbial processes in nitrogen cycle. Using lab-scale bioreactors, enrichment culture performing methane driven nitrate reduction was successfully obtained. The dominant archaea (AAA) were identified as a member of ANME (anaerobic methanotrophic archaea), which, in consortium with sulfate reducing bacteria (SRB), are known to mediate sulfate-dependent methane oxidation. Physiology and metagenomics analysis indicates that AAA could perform dissimilatory nitrate reduction to ammonia (DNRA) and oxidize methane via reverse methanogenesis. AAA-related rRNA sequences have been retrieved from various ecosystems, but the ecological importance of these archaea and their contribution to global carbon and nitrogen cycling is still not known. Additionally, nitric oxide dismutation (NOD) is a peculiar oxygen-forming process, recently proposed in the nitrite-dependent anaerobic methanotrophic NC10 bacterium. In contrast to canonical NO reduction, via NOD, NO is suggested to be disproportionated directly into N2 and O2, bypassing the ozone-depleting potent greenhouse gas nitrous oxide. Moreover, the formed O2 theoretically enables microbial aerobic catabolism in anoxic habitats, providing ecophysiological advantage for microbes to thrive on recalcitrant substrates in O2-limited environments. Thus the process could be ecologically important. After developing specific molecular tools targeting the enzyme, NO dismutase (Nod), that catalyze NO dismutation, we recovered diverse nod genes from various environments, including contaminated aquifers and wastewater treatment plants. One of our ongoing projects suggests that NOD microbes are involved in hydrocarbon degradation in one BTEX-contaminated aquifer in Germany. These data indicate that NO dismutation is widely spread in diverse microbes, however, currently little is known about the process and microorganisms with this capacity.
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