Thiosulfate, an important form of sulfur compounds, can serve as both electron donor and acceptor in various microorganisms. In Shewanella oneidensis, a bacterium renowned for respiratory versatility, thiosulfate reduction has long been recognized but whether it can catalyse thiosulfate oxidation remains elusive. In this study, we discovered that S. oneidensis is capable of thiosulfate oxidation, a process specifically catalysed by two periplasmic cytochrome c (cyt c) proteins, TsdA and TsdB, which act as the catalytic subunit and the electron transfer subunit respectively. In the presence of oxygen, oxidation of thiosulfate has priority over reduction. Intriguingly, thiosulfate oxidation negatively regulates the cyt c content in S. oneidensis cells, largely by reducing intracellular levels of cAMP, which as the cofactor modulates activity of global regulator Crp required for transcription of many cyt c genes. This unexpected finding provides an additional dimension to interplays between the respiration regulator and the respiratory pathways in S. oneidensis. Moreover, the data presented here identified S. oneidensis as the first bacterium known to date owning both functional thiosulfate reductase and dehydrogenase, and importantly, genomics analyses suggested that the number of bacterial species possessing this feature is rather limited.

中文翻译：

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硫还原希瓦氏菌中的硫代硫酸盐氧化及其对细胞色素 c 含量的意外影响

硫代硫酸盐是硫化合物的一种重要形式，在各种微生物中既可以作为电子供体，也可以作为受体。在Shewanella oneidensis中，一种以呼吸通用性着称的细菌，硫代硫酸盐的还原早已被认可，但它是否能催化硫代硫酸盐的氧化仍然是个未知数。在这项研究中，我们发现S. oneidensis能够进行硫代硫酸盐氧化，这一过程由两种周质细胞色素c (cyt c ) 蛋白 TsdA 和 TsdB 特异性催化，它们分别充当催化亚基和电子转移亚基。在氧气存在下，硫代硫酸盐的氧化优先于还原。有趣的是，硫代硫酸盐氧化负调节细胞色素cS. oneidensis细胞中的含量，主要是通过降低 cAMP 的细胞内水平，它作为辅助因子调节许多 cyt c基因转录所需的全局调节因子 Crp 的活性。这一出乎意料的发现为呼吸调节剂和S. oneidensis的呼吸途径之间的相互作用提供了一个额外的维度。此外，此处提供的数据将S. oneidensis确定为迄今为止已知的第一种同时拥有功能性硫代硫酸盐还原酶和脱氢酶的细菌，重要的是，基因组学分析表明，具有这种特征的细菌种类数量相当有限。