Heterotrophic bacteria dominate the sulfide oxidation process in coastal sediments

Sulfate reduction and sulfur oxidation are very active in coastal sediments. Together they shape the biogeochemistry and microbial ecology at hot places of organic matter metabolism. Compared to the well-studied sulfate reduction process, sulfur oxidation process is relatively lack of investigation. For a long time, autotrophic/mixotrophic bacteria were thought to be the main sulfur oxidation strains in sediments. Herein, we investigated the distribution of reduced sulfur compounds in differently layers of coastal sediments at the Yellow sea. We found that sulfide (H2S), sulfane sulfur (S0), and thiosulfate mainly accumulated in deep anaerobic sediments and were mostly oxidized in surface sediments (-3 cm in depth). Bacterial community analysis indicated that heterotrophic bacteria were dominating species in surface sediments. Metatranscriptome analysis showed that transcripts of flavocytochrome c sulfide dehydrogenase (FCC), persufide dioxygenase (PDO), and sulfite-oxidizing enzyme (SOE) were abundant in surface sediments. In addition, using a Roseobacterium (Ruegeria pomeroyi DSS-3) as the model strain, we investigated how FCC, PDO, and SOE work together to oxidize H2S to sulfate. This study clarified that heterotrophic bacteria are the main sulfur oxidation strains in coastal sediments.