1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA.
1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA [3] Institute of Marine Science - ISMAR, National Research Council of Italy, CNR, Ancona, Italy.
ISME J. 2014 Jul;8(7):1510-21. doi: 10.1038/ismej.2013.246. Epub 2014 Jan 16.
Despite the frequent isolation of nitrate-respiring Epsilonproteobacteria from deep-sea hydrothermal vents, the genes coding for the nitrate reduction pathway in these organisms have not been investigated in depth. In this study we have shown that the gene cluster coding for the periplasmic nitrate reductase complex (nap) is highly conserved in chemolithoautotrophic, nitrate-reducing Epsilonproteobacteria from deep-sea hydrothermal vents. Furthermore, we have shown that the napA gene is expressed in pure cultures of vent Epsilonproteobacteria and it is highly conserved in microbial communities collected from deep-sea vents characterized by different temperature and redox regimes. The diversity of nitrate-reducing Epsilonproteobacteria was found to be higher in moderate temperature, diffuse flow vents than in high temperature black smokers or in low temperatures, substrate-associated communities. As NapA has a high affinity for nitrate compared with the membrane-bound enzyme, its occurrence in vent Epsilonproteobacteria may represent an adaptation of these organisms to the low nitrate concentrations typically found in vent fluids. Taken together, our findings indicate that nitrate reduction is widespread in vent Epsilonproteobacteria and provide insight on alternative energy metabolism in vent microorganisms. The occurrence of the nap cluster in vent, commensal and pathogenic Epsilonproteobacteria suggests that the ability of these bacteria to respire nitrate is important in habitats as different as the deep-sea vents and the human body.
尽管从深海热液喷口经常分离到硝酸盐呼吸的 ε-变形菌，但这些生物体中硝酸盐还原途径的编码基因尚未得到深入研究。在本研究中，我们表明，来自深海热液喷口的化能自养、硝酸盐还原的 ε-变形菌的周质硝酸盐还原酶复合物（nap）基因簇高度保守。此外，我们还表明，napA 基因在喷口 ε-变形菌的纯培养物中表达，并在不同温度和氧化还原条件的深海喷口微生物群落中高度保守。在中温、弥散流喷口，与高温黑烟囱或低温、底物相关的群落相比，硝酸盐还原的 ε-变形菌的多样性更高。由于 NapA 对硝酸盐的亲和力高于膜结合酶，因此它在喷口 ε-变形菌中的存在可能代表了这些生物体对喷口流体中通常发现的低硝酸盐浓度的适应。总之，我们的研究结果表明，硝酸盐还原在喷口 ε-变形菌中广泛存在，并为喷口微生物的替代能量代谢提供了新的认识。nap 簇在喷口、共生和致病的 ε-变形菌中的存在表明，这些细菌呼吸硝酸盐的能力在深海喷口和人体等不同生境中都很重要。
