Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, 53115, Bonn, Germany.
ISME J. 2018 Oct;12(10):2479-2491. doi: 10.1038/s41396-018-0209-7. Epub 2018 Jun 21.
Dimethylsulfide (DMS) plays a globally significant role in carbon and sulfur cycling and impacts Earth's climate because its oxidation products serve as nuclei for cloud formation. While the initial steps of aerobic DMS degradation and the fate of its carbon atoms are reasonably well documented, oxidation of the contained sulfur is largely unexplored. Here, we identified a novel pathway of sulfur compound oxidation in the ubiquitously occurring DMS-degrader Hyphomicrobium denitrificans X that links the oxidation of the volatile organosulfur compound with that of the inorganic sulfur compound thiosulfate. DMS is first transformed to methanethiol from which sulfide is released and fully oxidized to sulfate. Comparative proteomics indicated thiosulfate as an intermediate of this pathway and pointed at a heterodisulfide reductase (Hdr)-like system acting as a sulfur-oxidizing entity. Indeed, marker exchange mutagenesis of hdr-like genes disrupted the ability of H. denitrificans to metabolize DMS and also prevented formation of sulfate from thiosulfate provided as an additional electron source during chemoorganoheterotrophic growth. Complementation with the hdr-like genes under a constitutive promoter rescued the phenotype on thiosulfate as well as on DMS. The production of sulfate from an organosulfur precursor via the Hdr-like system is previously undocumented and provides a new shunt in the biogeochemical sulfur cycle. Furthermore, our findings fill a long-standing knowledge gap in microbial dissimilatory sulfur metabolism because the Hdr-like pathway is abundant not only in chemoheterotrophs, but also in a wide range of chemo- and photolithoautotrophic sulfur oxidizers acting as key players in global sulfur cycling.
二甲基硫（DMS）在碳和硫循环中具有全球重要作用，并影响地球气候，因为其氧化产物可用作云形成的核心。虽然有氧 DMS 降解的初始步骤及其碳原子的命运得到了很好的记录，但对其中所含硫的氧化在很大程度上仍未得到探索。在这里，我们在普遍存在的 DMS 降解菌 Hyphomicrobium denitrificans X 中确定了一种新的硫化合物氧化途径，该途径将挥发性有机硫化合物的氧化与无机硫化合物硫代硫酸盐的氧化联系起来。DMS 首先转化为甲硫醇，从中释放出硫化物，并将其完全氧化为硫酸盐。比较蛋白质组学表明，硫代硫酸盐是该途径的中间体，并指出异双硫代还原酶（Hdr）样系统作为一种硫氧化实体起作用。事实上，标记交换突变 hdr 样基因破坏了 H. denitrificans 代谢 DMS 的能力，并且在化能有机异养生长期间作为额外的电子源提供硫代硫酸盐时也阻止了硫酸盐的形成。在组成型启动子下用 hdr 样基因进行互补挽救了硫代硫酸盐以及 DMS 上的表型。通过 Hdr 样系统从有机硫前体生产硫酸盐以前是没有记录的，这为生物地球化学硫循环提供了一个新的支路。此外，我们的发现填补了微生物异化硫代谢中长期存在的知识空白，因为 Hdr 样途径不仅在化能异养菌中丰富，而且在广泛的化能和光合自养硫氧化菌中也很丰富，这些菌是全球硫循环中的关键参与者。
