Nitrite Reductase of Nitrosomonas europaea Is Not Essential for Production of Gaseous Nitrogen Oxides and Confers Tolerance to Nitrite

A gene that encodes a periplasmic copper-type nitrite reductase (NirK) was identified in Nitrosomonas europaea. Disruption of this gene resulted in the disappearance of Nir activity in cell extracts. The nitrite tolerance of NirK-deficient cells was lower than that of wild-type cells. Unexpectedly, NirK-deficient cells still produced nitric oxide (NO) and nitrous oxide (N(2)O), the latter in greater amounts than that of wild-type cells. This demonstrates that NirK is not essential for the production of NO and N(2)O by N. europaea. Inactivation of the putative fnr gene showed that Fnr is not essential for the expression of nirK.

本研究在欧洲亚硝化单胞菌（Nitrosomonas europaea）中鉴定到一段编码周质铜型亚硝酸还原酶（periplasmic copper-type nitrite reductase，NirK）的基因。对该基因进行敲除后，细胞提取物中的亚硝酸还原酶活性完全消失。nirK缺陷型菌株的亚硝酸盐耐受性低于野生型菌株。出乎意料的是，nirK缺陷型菌株仍可产生一氧化氮（NO）与一氧化二氮（N₂O），且后者的产量高于野生型菌株。该结果证实，NirK并非欧洲亚硝化单胞菌产生NO和N₂O的必需因子。对推定的fnr基因进行失活处理后表明，Fnr并非nirK基因表达所必需的因子。