Kits K Dimitri, Klotz Martin G, Stein Lisa Y
Department of Biological Sciences, University of Alberta, CW405, Biological Sciences Building, Edmonton, AB, T6G 2E9, Canada.
Department of Biological Sciences, University of North Carolina, 9201 University City Boulevard, Charlotte, NC, 28223, USA.
Environ Microbiol. 2015 Sep;17(9):3219-32. doi: 10.1111/1462-2920.12772. Epub 2015 Mar 10.
Obligate methanotrophs belonging to the Phyla Proteobacteria and Verrucomicrobia require oxygen for respiration and methane oxidation; nevertheless, aerobic methanotrophs are abundant and active in low oxygen environments. While genomes of some aerobic methanotrophs encode putative nitrogen oxide reductases, it is not understood whether these metabolic modules are used for NOx detoxification, denitrification or other purposes. Here we demonstrate using microsensor measurements that a gammaproteobacterial methanotroph Methylomonas denitrificans sp. nov. strain FJG1(T) couples methane oxidation to nitrate reduction under oxygen limitation, releasing nitrous oxide as a terminal product. Illumina RNA-Seq data revealed differential expression of genes encoding a denitrification pathway previously unknown to methanotrophs as well as the pxmABC operon in M. denitrificans sp. nov. strain FJG1(T) in response to hypoxia. Physiological and transcriptome data indicate that genetic inventory encoding the denitrification pathway is upregulated only upon availability of nitrate under oxygen limitation. In addition, quantitation of ATP levels demonstrates that the denitrification pathway employs inventory such as nitrate reductase NarGH serving M. denitrificans sp. nov. strain FJG1(T) to conserve energy during oxygen limitation. This study unravelled an unexpected metabolic flexibility of aerobic methanotrophs, thereby assigning these bacteria a new role at the metabolic intersection of the carbon and nitrogen cycles.
属于变形菌门和疣微菌门的专性甲烷营养菌进行呼吸作用和甲烷氧化需要氧气；然而，需氧甲烷营养菌在低氧环境中数量众多且活性高。虽然一些需氧甲烷营养菌的基因组编码假定的氮氧化物还原酶，但尚不清楚这些代谢模块是用于氮氧化物解毒、反硝化作用还是其他目的。在这里，我们通过微传感器测量证明，一种γ-变形菌甲烷营养菌——反硝化甲基单胞菌新种FJG1(T)在氧气受限的情况下将甲烷氧化与硝酸盐还原耦合，释放一氧化二氮作为终产物。Illumina RNA测序数据揭示了反硝化甲基单胞菌新种FJG1(T)中编码一种甲烷营养菌以前未知的反硝化途径的基因以及pxmABC操纵子在低氧条件下的差异表达。生理和转录组数据表明，只有在氧气受限且有硝酸盐存在时，编码反硝化途径的基因库才会上调。此外，ATP水平的定量分析表明，反硝化途径利用诸如硝酸盐还原酶NarGH等物质，使反硝化甲基单胞菌新种FJG1(T)在氧气受限期间保存能量。这项研究揭示了需氧甲烷营养菌意想不到的代谢灵活性，从而赋予这些细菌在碳和氮循环的代谢交叉点上的新作用。
