Nitrate/Nitrite Reducing System in Staphylococcus carnosus: Functional analysis of NirR and NreABC

胭脂葡萄球菌传统上被用作生发酵香肠和干腌火腿生产的发酵剂。我们已经证明，S. carnosus通过两步机制将硝酸盐还原为氨。首先，硝酸盐被异化的硝酸盐还原酶还原为亚硝酸盐。亚硝酸盐在生长培养基中积累，并被nadh依赖的亚硝酸盐还原酶进一步还原。亚硝酸盐的还原只在没有硝酸盐的情况下发生。这两种酶的合成是由厌氧作用和硝酸盐和/或亚硝酸盐的存在诱导的。目前，我们已经鉴定出26个参与硝酸盐/亚硝酸盐还原的基因。我们的目的是阐明潜在的调节机制，确保电子受体氧、硝酸盐和亚硝酸盐的分层使用。NirR和NreABC被认为是鼠肉草中硝酸盐/亚硝酸盐还原系统的调节因子，我们对它们的作用模式很感兴趣。特别是，我们考虑到NreB，因为它可能参与感知和传输两种不同的信号：(i)氧气的存在，（ii）硝酸盐和/或亚硝酸盐的存在。了解牛油果中硝酸盐和亚硝酸盐还原的复杂调控将是研究该系统生物能量方面的工具。

Staphylococcus carnosus is traditionally used as a starter culture in the production of raw fermented sausages and dry-cured ham. We have shown that S. carnosus reduces nitrate to ammonia in a two-step mechanism. First, nitrate is reduced to nitrite by a dissimilatory nitrate reductase. Nitrite accumulates in the growth medium and is further reduced by a NADH-dependent nitrite reductase. Nitrite reduction only occurs in the absence of nitrate. Synthesis of both enzymes is induced by anaerobiosis and by the presence of nitrate and/or nitrite. At present, we have identified 26 genes which are involved in nitrate/nitrite reduction. Our aim is to elucidate the underlying regulatory mechanisms which ensure the hierarchical use of the electron acceptors oxygen, nitrate, and nitrite. NirR and NreABC are putative regulators of the nitrate/nitrite reducing system in S. carnosus and we are interested in their mode of action. Especially, we have NreB in view, since it might be involved in sensing and transmitting two different signals: (i) the presence of oxygen, and (ii) the presence of nitrate and/or nitrite. Understanding of the complex regulation of nitrate and nitrite reduction in S. carnosus would be a tool for studying the bioenergetic aspects of the system.