Endothiovibrio diazotrophicus gen. nov., sp nov., a novel nitrogen-fixing, sulfur-oxidizing gammaproteobacterium isolated from a salt marsh

A novel non-phototrophic, marine, sulfur-oxidizing bacterium, strain S-1(T), was isolated from a coastal salt marsh in Massachusetts, USA. Cells are Gram-stain-negative vibrios motile by means of a single polar unsheathed flagellum. S-1(T) is an obligate microaerophile with limited metabolic capacity. It grows chemolithoautotrophically utilizing sulfide and thiosulfate as electron donors, converting these compounds to sulfate, and the Calvin-Benson-Bassham cycle for carbon fixation. Cells of S-1(T) did not grow on any of a large number of organic carbon sources and there was no evidence for chemoorganoheterotrophic growth. Cells produced internal sulfur globules during growth on sulfide and thiosulfate. S-1(T) is strongly diazotrophic, as demonstrated by N-15(2) fixation and acetylene reduction activity by cells when a fixed nitrogen source is absent from the growth medium. The marine nature of this organism is evident from its ability to grow in 10 to 100% artificial seawater but not at lower concentrations and NaCl alone cannot substitute for sea salts. The major cellular fatty acids are C-16 : (1)omega 7c, C-16 : 0, and C-18 : 1 omega 7c. Phosphatidylethanolamine and phosphatidylglycerol are the major polar lipids. Q8 is the only respiratory quinone. S-1(T) genomic DNA has a G+C content of 67.6 mol%. Based on its 16S rRNA gene sequence, S-1(T) shows the closest phylogenetic relationship to non-phototrophic species within the family Thioalkalispiraceae of the class Gammaproteobacteria. The name Endothiovibrio diazotrophicus is proposed for this organism, with S-1(T) as the type strain (ATCC BAA-1439(T)=JCM 17961(T)).