The genus Dethiosulfovibrio consists of strictly anaerobic, moderately halotolerant, mesophilic bacteria that ferment proteins, amino acids, and some organic acids but not carbohydrates. Members of this genus are distinguished by their ability to reduce thiosulfate or elemental sulfur to sulfide in order to circumvent hydrogen buildup and increase growth rates. A new Dethiosulfovibrio strain, designated F2B, was recently isolated from an anaerobic digester in a marine recirculating aquaculture system, a significantly different environment than those of the other strains. Here, we report on the genome of strain F2B as a new species of the genus Dethiosulfovibrio. The name Dethiosulfovibrio faecalis is proposed. We also sequenced three other Dethiosulfovibrio species to expand the known genomic content of the genus.