Lü Chuanjuan, Xia Yongzhen, Liu Daixi, Zhao Rui, Gao Rui, Liu Honglei, Xun Luying
State Key Laboratory of Microbial Technology, Shandong University, Jinan, People's Republic of China.
State Key Laboratory of Microbial Technology, Shandong University, Jinan, People's Republic of China
Appl Environ Microbiol. 2017 Oct 31;83(22). doi: 10.1128/AEM.01610-17. Print 2017 Nov 15.
Production of sulfide (HS, HS, and S) by heterotrophic bacteria during aerobic growth is a common phenomenon. Some bacteria with sulfide:quinone oxidoreductase (SQR) and persulfide dioxygenase (PDO) can oxidize self-produced sulfide to sulfite and thiosulfate, but other bacteria without these enzymes release sulfide into the medium, from which HS can volatilize into the gas phase. Here, we report that H16, with the and genes encoding flavocytochrome sulfide dehydrogenases (FCSDs), also oxidized self-produced HS. A mutant in which and were deleted accumulated and released HS. When and were expressed in strain Pa3K with deletions of its and genes, the recombinant rapidly oxidized sulfide to sulfane sulfur. When PDO was also cloned into the recombinant, the recombinant with both FCSD and PDO oxidized sulfide to sulfite and thiosulfate. Thus, the proposed pathway is similar to the pathway catalyzed by SQR and PDO, in which FCSD oxidizes sulfide to polysulfide, polysulfide spontaneously reacts with reduced glutathione (GSH) to produce glutathione persulfide (GSSH), and PDO oxidizes GSSH to sulfite, which chemically reacts with polysulfide to produce thiosulfate. About 20.6% of sequenced bacterial genomes contain SQR, and only 3.9% contain FCSD. This is not a surprise, since SQR is more efficient in conserving energy because it passes electrons from sulfide oxidation into the electron transport chain at the quinone level, while FCSD passes electrons to cytochrome The transport of electrons from the latter to O conserves less energy. FCSDs are grouped into three subgroups, well conserved at the taxonomic level. Thus, our data show the diversity in sulfide oxidation by heterotrophic bacteria. Heterotrophic bacteria with SQR and PDO can oxidize self-produced sulfide and do not release HS into the gas phase. H16 has FCSD but not SQR, and it does not release HS. We confirmed that the bacterium used FCSD for the oxidation of self-produced sulfide. The bacterium also oxidized added sulfide. The common presence of SQRs, FCSDs, and PDOs in heterotrophic bacteria suggests the significant role of heterotrophic bacteria in sulfide oxidation, participating in sulfur biogeochemical cycling. Further, FCSDs have been identified in anaerobic photosynthetic bacteria and chemolithotrophic bacteria, but their physiological roles are unknown. We showed that heterotrophic bacteria use FCSDs to oxidize self-produced sulfide and extraneous sulfide, and they may be used for HS bioremediation.
异养细菌在有氧生长过程中产生硫化物（HS⁻、H₂S和S）是一种常见现象。一些具有硫化物：醌氧化还原酶（SQR）和过硫化物双加氧酶（PDO）的细菌可以将自身产生的硫化物氧化为亚硫酸盐和硫代硫酸盐，但其他没有这些酶的细菌会将硫化物释放到培养基中，HS⁻可从培养基中挥发到气相中。在此，我们报道具有编码黄素细胞色素硫化物脱氢酶（FCSD）的hmdA和hmdB基因的H16也能氧化自身产生的HS⁻。hmdA和hmdB缺失的突变体积累并释放HS⁻。当hmdA和hmdB在其hmdA和hmdB基因缺失的Pa3K菌株中表达时，重组体迅速将硫化物氧化为聚硫化物。当PDO也克隆到重组体中时，同时具有FCSD和PDO的重组体将硫化物氧化为亚硫酸盐和硫代硫酸盐。因此，所提出的途径类似于由SQR和PDO催化的途径，其中FCSD将硫化物氧化为多硫化物，多硫化物与还原型谷胱甘肽（GSH）自发反应生成谷胱甘肽过硫化物（GSSH），PDO将GSSH氧化为亚硫酸盐，亚硫酸盐与多硫化物发生化学反应生成硫代硫酸盐。约20.6%的已测序细菌基因组含有SQR，只有3.9%含有FCSD。这并不奇怪，因为SQR在能量守恒方面更有效，因为它将硫化物氧化产生的电子在醌水平传递到电子传递链中，而FCSD将电子传递给细胞色素c。从后者到O₂的电子传递保存的能量较少。FCSD分为三个亚组，在分类水平上保守性良好。因此，我们的数据显示了异养细菌在硫化物氧化方面的多样性。具有SQR和PDO的异养细菌可以氧化自身产生的硫化物，不会将HS⁻释放到气相中。H16具有FCSD但没有SQR，它不会释放HS⁻。我们证实该细菌使用FCSD氧化自身产生的硫化物。该细菌还能氧化添加的硫化物。异养细菌中普遍存在SQR、FCSD和PDO，这表明异养细菌在硫化物氧化中起重要作用，参与硫的生物地球化学循环。此外，在厌氧光合细菌和化能自养细菌中已鉴定出FCSD，但其生理作用尚不清楚。我们表明异养细菌利用FCSD氧化自身产生的硫化物和外来硫化物，它们可能用于HS⁻的生物修复。
