Deep-Sea In Situ Insights into the Formation of Zero-Valent Sulfur Driven by a Bacterial Thiosulfate Oxidation Pathway

Zero-valent sulfur (ZVS) distributes widely in the deep-sea cold seep, which is an important immediate in the sulfur cycle of cold seep. In our previous work, we described a novel thiosulfate oxidation pathway determined by thiosulfate dehydrogenase (TsdA) and thiosulfohydrolase (SoxB) mediating the conversion of thiosulfate to ZVS in the deep-sea cold seep bacterium Erythrobacter flavus 21-3. However, the occurrence and ecological role of this pathway in the deep-sea cold seep were obscure. Here, we cultured E. flavus 21-3 in the deep-sea cold seep for 10 days and demonstrated its capability of forming ZVS in the in situ field. Based on proteomic, stoichiometric analyses and microscopic observation, we found that this thiosulfate oxidation pathway benefited E. flavus 21-3 to adapt the cold seep conditions. Notably, ~25% metagenomes assembled genomes derived from the shallow sediments of cold seeps contained both tsdA and soxB, where presented abundant sulfur metabolism-related genes and active sulfur cycle. Our results suggested that the thiosulfate oxidation pathway determined by TsdA and SoxB existed across many bacteria inhabiting in the cold seep and frequently used by microbes to take part in the active cold seep biogeochemical sulfur cycle. IMPORTANCE The contribution of microbes to the deep-sea cold seep sulfur cycle has received considerable attention in recent years. In the previous study, we isolated E. flavus 21-3 from deep-sea cold seep sediments and described a novel thiosulfate oxidation pathway in the laboratorial condition. It provided a new clue about the formation of ZVS in the cold seep. However, because of huge differences between laboratory and in situ environment, whether bacteria perform the same thiosulfate oxidation pathway in the deep-sea cold seep should be further confirmed. In this work, we verified that E. flavus 21-3 formed ZVS using this pathway in deep-sea cold seep through in situ cultivation, which confirmed the importance of this thiosulfate oxidation pathway and provided an in situ approach to study the real metabolism of deep-sea microorganisms.