Physiological and Genomic Characterization of a Novel Obligately Chemolithoautotrophic, Sulfur-Oxidizing Bacterium of Genus Thiomicrorhabdus Isolated from a Coastal Sediment

Thiomicrorhabdus species, belonging to the family Piscirickettsiaceae in the phylum Pseudomonadotav are usually detected in various sulfur-rich marine environments. However, only a few bacteria of Thiomicrorhabdus have been isolated, and their ecological roles and environmental adaptations still require further understanding. Here, we report a novel strain, XGS-01(T), isolated from a coastal sediment, which belongs to genus Thiomicrorhabdus and is most closely related to Thiomicrorhabdus hydrogeniphila MAS2(T), with a sequence similarity of 97.8%. Phenotypic characterization showed that XGS-01(T) is a mesophilic, sulfur-oxidizing, obligate chemolithoautotrophy, with carbon dioxide as its sole carbon source and oxygen as its sole electron acceptor. During thiosulfate oxidation, strain XGS-01(T) can produce extracellular sulfur of elemental α-S(8), as confirmed via scanning electron microscopy and Raman spectromicroscopy. Polyphasic taxonomy results indicate that strain XGS-01(T) represents a novel species of the genus Thiomicrorhabdus, named Thiomicrorhabdus lithotrophica sp. nov. Genomic analysis confirmed that XGS-01(T) performed thiosulfate oxidation through a sox multienzyme complex, and harbored fcc and sqr genes for sulfide oxidation. Comparative genomics analysis among five available genomes from Thiomicrorhabdus species revealed that carbon fixation via the oxidation of reduced-sulfur compounds coupled with oxygen reduction is conserved metabolic pathways among members of genus Thiomicrorhabdus.