Sulfurospirillum diekertiae sp. nov., a tetrachloroethene- respiring bacterium isolated from contaminated soil

Two anaerobic, tetrachloroethene- (PCE-) respiring bacterial isolates, designated strain ACSDCET and strain ACSTCE, were characterized using a polyphasic approach. Cells were Gram- stain- negative, motile, non- spore- forming and shared a vibrioid- to spirillum- shaped morphology. Optimum growth occurred at 30 degrees C and 0.1-0.4 % salinity. The pH range for growth was pH 5.5- 7.5, with an optimum at pH 7.2. Hydrogen, formate, pyruvate and lactate as electron donors supported respiratory reductive dechlorination of PCE to cis-1,2-dichloroethene (cDCE) in strain ACSDCET and of PCE to trichloroethene (TCE) in strain ACSTCE. Both strains were able to grow with pyruvate under microaerobic conditions. Nitrate, elemental sulphur, and thiosulphate were alternative electron acceptors. Autotrophic growth was not observed and acetate served as carbon source for both strains. The major cellular fatty acids were C16: 1 omega 7c, C16:0, C14: 0 and C18:1 omega 7c. Both genomes feature a circular plasmid. Strains ACSDCET and ACSTCE were previously assigned to the candidate species 'Sulfurospirillum acididehalogenans'. Here, based on key genomic features and pairwise comparisons of whole- genome sequences, including average nucleotide identity, digital DNA- DNA hybridization and average amino acid identity, strains ACSDCET and ACSTCE, 'Ca. Sulfurospirillum diekertiae' strains SL2- 1 and SL2- 2, and the unclassified Sulfurospirillum sp. strain SPD- 1 are grouped into one distinct species separate from previously described Sulfurospirillum species. Compared to Sulfurospirillum multivorans and Sulfurospirillum halorespirans, which dechlorinate PCE to cDCE without substantial TCE accumulation, these five strains produce TCE or cDCE as the end product. In addition, some cellular fatty acids (e.g., C16: 0 3OH, C17:0 iso 3OH, C17:0 2OH) were detected in strains ACSDCET and ACSTCE but not in other Sulfurospirillum species. On the basis of phylogenetic, physiological and phenotypic characteristics, 'Ca. Sulfurospirillum acididehalogenans' and 'Ca. Sulfurospirillum diekertiae' are proposed to be merged into one novel species within the genus Sulfurospirillum, for which the name Sulfurospirillum diekertiae sp. nov. is proposed. The type strain is ACSDCET (=JCM 33349T= KCTC 15819T=CGMCC 1.5292T).

Automated summary

Two anaerobic bacterial isolates, ACSDCET and ACSTCE, capable of respiring tetrachloroethene (PCE), were characterized. These strains showed unique morphological and physiological characteristics, including optimum growth conditions, electron donors, and acceptors. Genomic analysis further confirmed the distinction of these strains from other Sulfurospirillum species, proposing a new species named Sulfurospirillum diekertiae sp. nov. This study provides important insights into the diversity and functionalities of PCE-respiring bacteria.