Desulfitobacterium elongatum sp. nov. NIT-TF6 Isolated from Trichloroethene-Dechlorinating Culture with Formate

A strictly anaerobic bacterium denoted as strain NIT-TF6 of the genus Desulfitobacterium was isolated from a trichloroethene-dechlorinating culture with formate. Cells were straight rods of 1.6–6 µm long and 0.25–0.5 µm in diameter and used H₂, lactate, pyruvate, and malate as electron donors and thiosulfate and Fe (III)-citrate as electron acceptors. The genome of strain NIT-TF6 was 4.8 Mbp in size and included nine 16S rRNA genes. Phylogenetic analysis based on 16S rRNA sequences showed that NIT-TF6 shared the highest sequence similarity (96.39%) with Desulfitobacterium hafniense DCB-2ᵀ, forming an independent clade in the phylogenetic tree. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values between strain NIT-TF6 and other Desulfitobacterium species ranged from 15.9 to 16.9% and from 71.68 to 72.51%, respectively. These are well below the thresholds for species delineation. A distinguishing feature of strain NIT-TF6 was its possession of both L-lactate dehydrogenase (L-LDH) and D-lactate dehydrogenase (D-LDH), in contrast to other Desulfitobacterium strains that exclusively express D-LDH. Based on the dDDH and ANI results, combined with physiological, phylogenetic, morphological, biochemical, genomic, and metabolic iron-related characteristics, strain NIT-TF6 has been proposed as a novel species within the genus Desulfitobacterium. The name Desulfitobacterium elongatum sp. nov. has been proposed for this strain, with NIT-TF6ᵀ designated as the type strain.