Department of Microbiology, University of Tennessee, Knoxville, Tennessee, USA.
Department of Biochemistry and Cellular and Molecular Biology, University of Tennessee, Knoxville, Tennessee, USA.
Appl Environ Microbiol. 2018 Jan 31;84(4). doi: 10.1128/AEM.01985-17. Print 2018 Feb 15.
The versatile soil bacterium lacks the hallmark denitrification genes and (encoding NO→NO reductases) and couples growth to NO reduction to NH (respiratory ammonification) and to NO reduction to N also grows by reducing Fe(III) to Fe(II), which chemically reacts with NO to form NO (i.e., chemodenitrification). Following the addition of 100 μmol of NO or NO to Fe(III)-grown axenic cultures of , 54 (±7) μmol and 113 (±2) μmol NO-N, respectively, were produced and subsequently consumed. The conversion of NO to N in the presence of Fe(II) through linked biotic-abiotic reactions represents an unrecognized ecophysiology of The new findings demonstrate that the assessment of gene content alone is insufficient to predict microbial denitrification potential and N loss (i.e., the formation of gaseous N products). A survey of complete bacterial genomes in the NCBI Reference Sequence database coupled with available physiological information revealed that organisms lacking or but with Fe(III) reduction potential and genes for NO and NO reduction are not rare, indicating that NO reduction to N through linked biotic-abiotic reactions is not limited to Considering the ubiquity of iron in soils and sediments and the broad distribution of dissimilatory Fe(III) and NO reducers, denitrification independent of NO-forming NO reductases (through combined biotic-abiotic reactions) may have substantial contributions to N loss and NO flux. Current attempts to gauge N loss from soils rely on the quantitative measurement of and genes and/or transcripts. In the presence of iron, the common soil bacterium is capable of denitrification and the production of N without the key denitrification genes and Such chemodenitrifiers denitrify through combined biotic and abiotic reactions and have potentially large contributions to N loss to the atmosphere and fill a heretofore unrecognized ecological niche in soil ecosystems. The findings emphasize that the comprehensive understanding of N flux and the accurate assessment of denitrification potential can be achieved only when integrated studies of interlinked biogeochemical cycles are performed.
多功能土壤细菌缺乏标志性的反硝化基因和（编码 NO→NO 还原酶），并将生长与 NO 还原为 NH（呼吸氨化）和将 NO 还原为 N 偶联，也通过将 Fe(III)还原为 Fe(II)生长，Fe(II)与 NO 化学反 应形成 NO（即化学反硝化）。在向 Fe(III)培养的无菌培养物中添加 100 μmol 的 NO 或 NO 后，分别产生了 54（±7）μmol 和 113（±2）μmol 的 NO-N，随后被消耗。在 Fe(II)存在下通过连接的生物-非生物反应将 NO 转化为 N，代表了 一种未被认识的生态生理学。新的发现表明，仅评估基因含量不足以预测微生物反硝化潜力和 N 损失（即气态 N 产物的形成）。对 NCBI 参考序列数据库中完整细菌基因组的调查以及现有的生理信息表明，缺乏或但具有 Fe(III)还原潜力和 NO 和 NO 还原基因的生物体并不罕见，这表明通过连接的生物-非生物反应将 NO 还原为 N 并不仅限于。考虑到铁在土壤和沉积物中的普遍存在以及异化 Fe(III)和 NO 还原菌的广泛分布，不依赖于形成 NO 的 NO 还原酶的反硝化（通过联合的生物-非生物反应）可能对 N 损失和 NO 通量有实质性贡献。目前评估土壤中 N 损失的尝试依赖于定量测量和/或转录物。在铁的存在下，常见的土壤细菌能够进行反硝化作用并产生 N，而无需关键的反硝化基因和。这种化学反硝化菌通过联合的生物和非生物反应进行反硝化，并且可能对大气中的 N 损失做出很大贡献，并填补了土壤生态系统中一个以前未被认识的生态位。这些发现强调，只有通过进行相互关联的生物地球化学循环的综合研究，才能实现对 N 通量的全面理解和对反硝化潜力的准确评估。
