Physiology of dissimilatory nitrate reduction to ammonium (DNRA) in rice paddy soil isolates acquired with a newly developed high-throughput screening method

Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) has recently gained attention as a nitrogen dissimilation pathway that may potentially be harnessed to alleviate nitrogen loss resulting from denitrification. Up until now, physiological characteristics of DNRA-catalyzing bacteria inhabiting agricultural soils has remained largely unexplored, as DNRA is often outcompeted by denitrification when soils are anaerobically enriched with NO3- provided as the electron acceptor and thus, targeted enrichment or isolation of DNRA-catalyzing microorganisms has been an onerous task. In this study, several microbial isolates capable of DNRA have been isolated from denitrification-dominant agricultural soils using a simple high-throughput DNRA screening method. The DNRA reactions in six of these isolates, each assigned to a disparate genus according to 16S rRNA phylogeny, were examined. All six isolates carried nrfA and/or nirB, and the isolate affiliated to the Bacillus genus possessed a clade II nosZ gene and was capable of N2O reduction.

异化硝酸盐/亚硝酸盐还原产铵（Dissimilatory nitrate/nitrite reduction to ammonium, DNRA）作为一类氮异化代谢途径，近年来因其可用于缓解反硝化作用引发的氮素流失而受到广泛关注。截至目前，农田土壤中栖息的DNRA催化细菌的生理特征仍未得到充分解析，这是因为当以硝酸根作为电子受体对土壤进行厌氧富集时，DNRA过程常被反硝化作用所竞争，因此靶向富集或分离DNRA催化微生物始终是一项颇具挑战性的工作。本研究采用一种简便的高通量DNRA筛选方法，从以反硝化作用为主的农田土壤中分离得到了多株具备DNRA活性的微生物分离株。研究对其中6株分离株的DNRA反应进行了检测，基于16S rRNA系统发育分析，这6株分离株分属于不同的属。6株分离株均携带nrfA和/或nirB基因，其中隶属于芽孢杆菌（Bacillus）属的分离株携带进化枝II型nosZ基因，且具备一氧化二氮（N2O）还原能力。