Arcobacter pernae sp. nov. and Arcobacter rhizosphaerae sp. nov., two novel bacterial species isolated from the seagrass bed.

Three bacterial strains, YIC-464T (isolated from the intestinal tract of Perna mussels), YIC-310T and YIC-80 (both isolated from rhizosphere soil), were obtained from a seagrass bed in Weihai, PR China. A polyphasic taxonomic study revealed that strains YIC-464T and YIC-310T represent two novel species within the genus Arcobacter. Phylogenetic analysis based on the 16S rRNA gene sequence showed that the closest relative of strains YIC-464T, YIC-310T and YIC-80 is Arcobacter roscoffensis KCTC 52423T, with sequence similarities of 96.8, 98.0 and 98.0%, respectively. Furthermore, multilocus phylogenetic analysis based on five concatenated housekeeping genes (atpA, gyrB, hsp60, rpoB and gyrA) demonstrated that strains YIC-464T and YIC-310T form distinct branches separate from other Arcobacter species. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between these strains and their closely related species were below the species delineation thresholds. Specifically, the ANI and dDDH values between YIC-464T and YIC-310T were 85.7 and 30.0%, respectively, while those between YIC-310T and YIC-80 were 99.0 and 90.9%, respectively. These results confirm that strains YIC-464T and YIC-310T represent two novel species, whereas YIC-310T and YIC-80 belong to the same species. Menaquinone-6 was identified as the sole respiratory quinone in all strains. The major fatty acids (>10.0%) included C16 : 0, summed feature 3 (C16 : 1  ω7c and/or C16 : 1  ω6c) and summed feature 8 (C18 : 1  ω7c and/or C18 : 1  ω6c). Phenotypic characterization further differentiated these strains from other species. Therefore, we propose two new species: Arcobacter pernae sp. nov. and Arcobacter rhizosphaerae sp. nov., with type strains YIC-464T (=MCCC 1K09442T=KCTC 102325T) and YIC-310T (=MCCC 1K09441T=KCTC 102324T), respectively.