Abstract
Two sulfur-oxidizing bacterial strains, FCG-A2(T) and FCG-A23(T), were isolated from coastal sediments collected in Fangchenggang, Guangxi Province, China. Phylogenetic analyses based on 16S rRNA gene and whole-genome sequences placed strain FCG-A2(T) within the genus Pseudothioclava and strain FCG-A23(T) within the genus Terasakiella. Genomic relatedness (ANI, AAI, dDDH, and POCP) to the closest described taxa was below the accepted species thresholds, demonstrating that both isolates represent novel species. Strain FCG-A2(T) grew at 15-35 °C (optimum 25-30 °C), at pH 5.0-10.0 (optimum pH 8.0), and with 1-4% (w/v) NaCl concentrations (optimum 3%). Strain FCG-A23(T) grew at 20-33 °C (optimum 25-30 °C), at pH 6.0-9.0 (optimum, pH 8.0), and with 2-6% (w/v) NaCl (optimum 2%). For both strains, ubiquinone-10 was the major respiratory quinone, and the predominant fatty acids were summed feature 3 (C(16:1)ω7c and/or C(16:1)ω6c) and summed feature 8 (C(18:1)ω7c and/or C(18:1)ω6c); strain FCG-A2(T) additionally contained C(16:0) as a major fatty acid. Both strains oxidized thiosulfate to sulfate, consistent with the presence of genes encoding the Sox system and assimilatory sulfate reduction pathways. Comparative genome annotation further suggested a broader carbohydrate-degradation potential in FCG-A2(T) than in FCG-A23(T), implying a wider ecological distribution and greater opportunities for FCG-A2(T) to perform sulfur oxidation across habitats. The draft genomes had G + C contents of 62.09% (FCG-A2(T)) and 49.06% (FCG-A23(T)). Based on these results, we propose Pseudothioclava alba sp. nov. (type strain FCG-A2(T) = MCCC 1K08969(T) = KCTC 8462(T)) and Terasakiella sediminum sp. nov. (type strain FCG-A23(T) = MCCC 1K08972(T) = KCTC 8464(T)).