Comparative Genomics of Strains D-401 and D-402 with Contrasting Physiology but Extremely High Level of Genomic Identity.

Representatives of filamentous colorless sulfur-oxidizing bacteria often dominate in sulfide biotopes, preventing the diffusion of toxic sulfide into the water column. One of the most intriguing groups is a recently described including strains D-401 and D-402. Both strains have identical genes encoding enzymes which are involved in the oxidation of hydrogen sulfide and thiosulfate. Surprisingly, the strain D-401 is not capable to grow lithotrophically in the presence of reduced sulfur compounds and to accumulate elemental sulfur inside the cells, in contrast to the D-402 strain. In general, genomes of D-401 and D-402 have an extremely high level of identity and only differ in 1 single-letter substitution, 4 single-letter indels, and 16 long inserts. Among long inserts, 14 are transposons. It was shown that in the D-401 strain, a gene coding for a sulfur globule protein was disrupted by one of the mentioned transposons. Based on comparative genomics, RT-qPCR, and HPLC-MS/MS, we can conclude that this gene plays a crucial role in the formation of the sulfur globules inside the cells, and the disruption of its function prevents lithotrophic growth of in the presence of reduced sulfur compounds.