Paralimibaculum aggregatum gen. nov. sp. nov. and Biformimicrobium ophioploci gen. nov. sp. nov., two novel heterotrophs from brittle star Ophioplocus japonicus.

Abstract

Two novel Gram-stain-negative, strictly aerobic, halophilic and non-motile bacterial strains, designated NKW23^T and NKW57^T, were isolated from a brittle star Ophioplocus japonicus collected from a tidal pool in Wakayama, Japan. The results of phylogenetic analysis based on 16S rRNA gene sequences indicated that NKW23^T represented a member of the family Paracoccaceae, with Limibaculum halophilum CAU 1123^T as its closest relative (94.4% sequence identity). NKW57^T was identified as representing a member of the family Microbulbiferaceae, with up to 94.9% sequence identity with its closest relatives. Both strains displayed average nucleotide identity (ANI) and digital DNA-DNA hybridisation (dDDH) values below the species delimitation threshold against their closest relatives. Additionally, amino acid identity (AAI) values of both strains fell below the genus-defining threshold. Phylogenetic trees based on genome sequences indicated that NKW23^T formed a novel lineage, branching deeply prior to the divergence of the genera Limibaculum and Thermohalobaculum, with an evolutionary distance (ED) of 0.31-0.32, indicative of genus-level differentiation. NKW57^T similarly formed a distinct lineage separate from the species of the genus Microbulbifer. The major respiratory quinones of NKW23^T and NKW57^T were ubiquinone-10 (Q-10) and Q-8, respectively. The genomic DNA G+C contents of NKW23^T and NKW57^T were 71.4 and 58.8%, respectively. On the basis of the physiological and phylogenetic characteristics, it was proposed that these strains should be classified as novel species representing two novel genera: Paralimibaculum aggregatum gen. nov., sp. nov., with strain NKW23^T (=JCM 36220^T=KCTC 8062^T) as the type strain, and Biformimicrobium ophioploci gen. nov., sp. nov., with strain NKW57^T (=JCM 36221^T=KCTC 8063^T) as the type strain.