Department of Microbiology, Bose Institute, P-1/12 CIT Scheme VIIM, Kolkata-700054, India.
Present address: National Institute of Cholera and Enteric Diseases (NICED), P- C.I.T. Scheme XM, Beleghata, 33, CIT Rd, Beleghata, Kolkata - 700054, India.
Microbiology (Reading). 2020 Apr;166(4):386-397. doi: 10.1099/mic.0.000890. Epub 2020 Jan 30.
Chemolithotrophic sulfur oxidation represents a significant part of the biogeochemical cycling of this element. Due to its long evolutionary history, this ancient metabolism is well known for its extensive mechanistic and phylogenetic diversification across a diverse taxonomic spectrum. Here we carried out whole-genome sequencing and analysis of a new betaproteobacterial isolate, SBSA, which is found to oxidize thiosulfate via the formation of tetrathionate as an intermediate. The 4.7 Mb SBSA genome was found to encompass a operon, plus single thiosulfate dehydrogenase () and sulfite : acceptor oxidoreductase () genes. Recombination-based knockout of revealed that the entire thiosulfate is first converted to tetrathionate by the activity of thiosulfate dehydrogenase (TsdA) and the Sox pathway is not functional in this bacterium despite the presence of all necessary genes. The ∆ and ∆ knockout mutants exhibited a wild-type-like phenotype for thiosulfate/tetrathionate oxidation, whereas ∆ ∆ and ::Kan mutants only oxidized thiosulfate up to tetrathionate intermediate and had complete impairment in tetrathionate oxidation. The substrate-dependent O consumption rate of whole cells and the sulfur-oxidizing enzyme activities of cell-free extracts, measured in the presence/absence of thiol inhibitors/glutathione, indicated that glutathione plays a key role in SBSA tetrathionate oxidation. The present findings collectively indicate that the potential glutathione : tetrathionate coupling in involves a novel enzymatic component, which is different from the dual-functional thiol dehydrotransferase (ThdT), while subsequent oxidation of the sulfur intermediates produced (e.g. glutathione : sulfodisulfane molecules) may proceed via the iterative action of .
化能自养硫氧化代表了该元素生物地球化学循环的重要组成部分。由于其悠久的进化历史，这种古老的代谢途径以其在广泛的分类范围内的广泛机制和系统发育多样化而闻名。在这里，我们对一种新的β变形杆菌分离株 SBSA 进行了全基因组测序和分析，该分离株被发现通过形成连四硫酸盐作为中间体来氧化硫代硫酸盐。发现 4.7 Mb 的 SBSA 基因组包含一个 操纵子，加上单个硫代硫酸盐脱氢酶 () 和亚硫酸盐：接受体氧化还原酶 () 基因。基于重组的 基因敲除表明，整个硫代硫酸盐首先通过硫代硫酸盐脱氢酶 (TsdA) 的活性转化为连四硫酸盐，尽管存在所有必需的 基因，但 Sox 途径在该细菌中不起作用。Δ 和 Δ 敲除突变体对硫代硫酸盐/连四硫酸盐的氧化表现出与野生型相似的表型，而 Δ Δ 和 ::Kan 突变体仅将硫代硫酸盐氧化至连四硫酸盐中间体，并且完全不能氧化连四硫酸盐。在存在/不存在巯基抑制剂/谷胱甘肽的情况下，整个细胞的底物依赖性 O 消耗率和无细胞提取物中的硫氧化酶活性的测量表明，谷胱甘肽在 SBSA 连四硫酸盐氧化中起关键作用。综上所述，这些发现表明， 中的潜在谷胱甘肽-连四硫酸盐偶联可能涉及一种新的酶促成分，不同于双功能硫醇脱氢酶 (ThdT)，而随后产生的硫中间产物（例如谷胱甘肽-亚硫酸二硫键分子）的氧化可能通过 的迭代作用进行。
