Intolerable sulfide emission was spotted at several areas in tidal flats of the Ariake Sea, Japan. Sulfide is naturally produced in tidal flats and rapidly oxidized by sulfur-oxidizing bacteria (SOB). This makes them important players in controlling released sulfide by sulfate-reducing bacteria. A part of SOB can grow heterotrophically and we isolated them from a conserved muddy tidal flat in the Midorikawa Estuary, Kumamoto. The obtained heterotrophs oxidized sulfur compounds in presence of organic carbon. Various metabolic pathways were detected among them during oxidation of thiosulfate and an isolate showed capability of sulfide oxidation. Phylogenetically, they were close-related to the genera Paracoccus, Bacillus, Dyella, and Pseudomonas. This suggested that the isolated SOB were affiliated to diverse classes and functioned diversely in oxidative side of the sulfur cycle. Additionally, population number of heterotrophic SOB was detected in high abundance, suggesting that they played a significant role in the sulfur cycle of the Midorikawa Tidal Flat.
Key words: Heterotrophic sulfur-oxidizing bacteria, isolation, tidal flat, thiosulfate, sulfide.