MMR_2024v14n3

Molecular Microbiology Research 2024, Vol.14, No.3, 119-123 http://microbescipublisher.com/index.php/mmr 119 Scientific Review Open Access NrfA Enzyme: The Bridge Connecting Microbes and Environmental Nitrogen Dynamics ManmanLi Hainan Institute of Tropical Agricultural Resources, Sanya, 572024, Hainan, China Corresponding email: lmm314.editor@gmail.com Molecular Microbiology Research, 2024, Vol.14, No.3 doi: 10.5376/mmr.2024.14.0013 Received: 15 Mar., 2024 Accepted: 26 Apr., 2024 Published: 12 May, 2024 Copyright © 2024 Li, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Li M.M., 2024, NrfA enzyme: the bridge connecting microbes and environmental nitrogen dynamics, Molecular Microbiology Research, 14(3):119-123 (doi: 10.5376/mmr.2024.14.0013) The paper Diversity and ecology of NrfA-dependent ammonifying microorganisms was published on March 9, 2024, in the journal Trends in Microbiology. Authored by Aurélien Saghaï and Sara Hallin from the Swedish University of Agricultural Sciences, among others, this study focuses on NrfA-dependent ammonifying microorganisms. These are a diverse group of microorganisms that reduce nitrate to ammonia, significantly impacting nitrogen retention across various ecosystems. These organisms play a crucial role in the nitrogen cycle. The article discusses in detail their diversity, physiological roles, and ecological significance in terrestrial and aquatic environments. 1 Experimental Data Analysis The key findings of the experiment are mainly reflected in two aspects: First, in terms of diversity and ecological environment: (1) NrfA-dependent ammonifying microorganisms are widely present in both terrestrial and aquatic environments, with a rich variety of species and broad distribution. (2) These microorganisms demonstrate the capability to reduce nitrate, especially under oxygen-limited conditions, across various environments. The second aspect concerns physiological functions: (1) The NrfA enzyme is a key biocatalyst linking nitrate reduction to ammonia, through which these microorganisms contribute to nitrogen retention in the environment. (2) The NrfA enzyme, by acting in the space between the outer membranes of bacterial cells, can directly reduce nitrite to ammonia. Figure 1 presents a conceptual schematic of the inorganic nitrogen cycle, revealing the pathways of nitrogen transformation in the natural environment. The nitrogen cycle primarily includes: (1) atmospheric nitrogen fixation, (2) mineralization of organic nitrogen, (3) nitrification, (4) denitrification, (5) ammonification of nitrate, (6) anaerobic ammonium oxidation, and (7) assimilation of ammonia and nitrate. The products of each stage and some intermediate products are indicated by their chemical names in the diagram. Nitrogen is lost from ecosystems through leaching of nitrate and gaseous losses. This cyclic process is fundamental for understanding the flow of nitrogen in soil, water, and air and its impact on ecosystems. Figure 2 provides a detailed depiction of the dimeric structure of the NrfA enzyme in Escherichia coli and its role in the electron transport chain from formate to nitrite. Panel A shows the three-dimensional structure of the NrfA homodimer, each monomer containing five heme groups, along with calcium ions and iron atoms. Panel B illustrates the electron transfer during the respiratory nitrite ammonification process, involving NrfH or NrfBCD as electron carriers. Through this process, formate is oxidized on the cell membrane, generating proton motive force that drives electrons through the complex, ultimately achieving the reduction of nitrite. This complex reaction process is crucial for intracellular energy conversion and material cycling.

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