Pyne Prosenjit, Alam Masrure, Rameez Moidu Jameela, Mandal Subhrangshu, Sar Abhijit, Mondal Nibendu, Debnath Utsab, Mathew Boby, Misra Anup Kumar, Mandal Amit Kumar, Ghosh Wriddhiman
Department of Microbiology, Bose Institute, P-1/12 CIT Scheme VIIM, Kolkata 700054, India.
Division of Molecular Medicine, Bose Institute, P-1/12 CIT Scheme VIIM, Kolkata 700054, India.
Mol Microbiol. 2018 Jul;109(2):169-191. doi: 10.1111/mmi.13972. Epub 2018 Jun 8.
The SoxXAYZB(CD) -mediated pathway of bacterial sulfur-chemolithotrophy explains the oxidation of thiosulfate, sulfide, sulfur and sulfite but not tetrathionate. Advenella kashmirensis, which oxidizes tetrathionate to sulfate, besides forming it as an intermediate during thiosulfate oxidation, possesses a soxCDYZAXOB operon. Knock-out mutations proved that only SoxBCD is involved in A. kashmirensis tetrathionate oxidation, whereas thiosulfate-to-tetrathionate conversion is Sox independent. Expression of two glutathione metabolism-related proteins increased under chemolithotrophic conditions, as compared to the chemoorganotrophic one. Substrate-dependent oxygen consumption pattern of whole cells, and sulfur-oxidizing enzyme activities of cell-free extracts, measured in the presence/absence of thiol inhibitors/glutathione, corroborated glutathione involvement in tetrathionate oxidation. Furthermore, proteome analyses detected a sulfite:acceptor oxidoreductase (SorAB) exclusively under chemolithotrophic conditions, while expression of a methanol dehydrogenase (XoxF) homolog, subsequently named thiol dehydrotransferase (ThdT), was found to increase 3- and 10-fold during thiosulfate-to-tetrathionate conversion and tetrathionate oxidation respectively. A thdT knock-out mutant did not oxidize tetrathionate but converted half of the supplied 40 mM S-thiosulfate to tetrathionate. Knock-out of another thiosulfate dehydrogenase (tsdA) gene proved that both ThdT and TsdA individually converted ∼ 20 mM S-thiosulfate to tetrathionate. The overexpressed and isolated ThdT protein exhibited PQQ-dependent thiosulfate dehydrogenation, whereas its PQQ-independent thiol transfer activity involving tetrathionate and glutathione potentially produced a glutathione:sulfodisulfane adduct and sulfite. SoxBCD and SorAB were hypothesized to oxidize the aforesaid adduct and sulfite respectively.
SoxXAYZB(CD)介导的细菌硫化学自养途径解释了硫代硫酸盐、硫化物、硫和亚硫酸盐的氧化，但不能解释连四硫酸盐的氧化。克什米尔阿德文氏菌除了在硫代硫酸盐氧化过程中将连四硫酸盐作为中间产物形成外，还能将连四硫酸盐氧化为硫酸盐，它拥有一个soxCDYZAXOB操纵子。基因敲除突变证明，在克什米尔阿德文氏菌中只有SoxBCD参与连四硫酸盐的氧化，而硫代硫酸盐到连四硫酸盐的转化与Sox无关。与化能有机营养条件相比，在化能无机营养条件下，两种与谷胱甘肽代谢相关的蛋白质的表达增加。在存在/不存在硫醇抑制剂/谷胱甘肽的情况下测量的全细胞底物依赖性耗氧模式以及无细胞提取物的硫氧化酶活性，证实了谷胱甘肽参与连四硫酸盐的氧化。此外，蛋白质组分析仅在化能无机营养条件下检测到一种亚硫酸盐：受体氧化还原酶（SorAB），而在硫代硫酸盐到连四硫酸盐的转化过程中，一种甲醇脱氢酶（XoxF）同源物的表达增加了3倍，在连四硫酸盐氧化过程中该同源物的表达增加了10倍，该同源物后来被命名为硫醇脱氢酶（ThdT）。一个thdT基因敲除突变体不能氧化连四硫酸盐，但能将所提供的40 mM硫代硫酸盐的一半转化为连四硫酸盐。另一个硫代硫酸盐脱氢酶（tsdA）基因的敲除证明，ThdT和TsdA都能分别将约20 mM硫代硫酸盐转化为连四硫酸盐。过表达和分离的ThdT蛋白表现出依赖于吡咯喹啉醌（PQQ）的硫代硫酸盐脱氢作用，而其涉及连四硫酸盐和谷胱甘肽的不依赖于PQQ的硫醇转移活性可能产生谷胱甘肽：磺二硫烷加合物和亚硫酸盐。推测SoxBCD和SorAB分别氧化上述加合物和亚硫酸盐。
