Thermococcus paralvinellae sp. nov. and Thermococcus cleftensis sp. nov. of hyperthermophilic heterotrophs from deep-sea hydrothermal vents

Two heterotrophic hyperthermophilic strains, ES1^Tand CL1^T, were isolated from Paralvinella sp. polychaete worms collected from active hydrothermal vent chimneys in the north-eastern Pacific Ocean. Both were obligately anaerobic and produced H₂S in the presence of elemental sulfur and H₂. Complete genome sequences are available for both strains. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strains are more than 97% similar to most other species of the genus Thermococcus. Therefore, overall genome relatedness index analyses were performed to establish that these strains are novel species. For each analysis, strain ES1^Twas determined to be most similar to Thermococcus barophilus MPT, while strain CL1^Twas determined to be most similar to Thermococcus sp. 4557. The average nucleotide identity scores for these strains were 84% for strain ES1^Tand 81% for strain CL1^T, genome-to-genome direct comparison scores were 23% for strain ES1^Tand 47% for strain CL1^T, and the species identification scores were 89% for strain ES1^Tand 88% for strain CL1^T. For each analysis, strains ES1^Tand CL1^Twere below the species delineation cut-off. Therefore, based on their whole genome sequences, strains ES1^Tand CL1^Tare suggested to represent novel species of the genus Thermococcus for which the names Thermococcus paralvinellae sp. nov. and Thermococcus cleftensis sp. nov. are proposed, respectively. The type strains are ES1T (=DSM 27261^T=KACC 17923T) and CL1T (=DSM 27260^T=KACC 17922^T).