Galbibacter pacificus sp. nov., isolated from surface seawater of the western Pacific Ocean and transfer of Joostella marina to the genus Galbibacter as Galbibacter orientalis nom. nov. and emended description of the genus Galbibacter

Abstract

Two Gram-stain-negative, non-motile, non-spore-forming, strictly aerobic and rod-shaped bacterial strains, CMA-7^T and CAA-3, were isolated from surface seawater samples collected from the western Pacific Ocean. Phylogeny of 16S rRNA gene sequences indicated they were related to the genera Galbibacter and Joostella and shared 95.1, 90.9 and 90.8% sequence similarity with G. mesophilus Mok-17^T, J. marina DSM 19592^T and G. marinus ck-I2-15^T, respectively. Phylogenomic analysis showed that the two strains, together with the members of the genera Galbibacter and Joostella, formed a monophyletic clade that could also be considered a monophyletic taxon. This distinctiveness was supported by amino acid identity and percentage of conserved proteins indices, phenotypic and chemotaxonomic characteristics and comparative genomics analysis. Digital DNA‒DNA hybridization values and average nucleotide identities between the two strains and their closest relatives were 18.0-20.8 % and 77.7-79.3 %, respectively. The principal fatty acids were iso-C_{15 : 0}, iso-C_{17 : 0} 3-OH, iso-C_{15 : 1} G, Summed Feature 3 (C_{16 : 1} ω7c/C_{16 : 1} ω6c or C_{16 : 1} ω6c/C1_{6 : 1} ω7c), Summed Feature 9 (iso-C_{17 : 1} ω9c or C_{16 : 0} 10-methyl), and C_{15 : 0} 3-OH. The predominant respiratory quinone was MK-6. The polar lipids were phosphatidylethanolamine, aminolipid, aminophospholipid, phospholipid, phosphoglycolipid, glycolipid and unknown polar lipid. The genomic DNA G+C content of strains CMA-7^T and CAA-3 was both 38.4 mol%. Genomic analysis indicated they have the potential to degrade cellulose and chitin. Based on the polyphasic evidence presented in this study, the two strains represent a novel species within the genus Galbibacter, for which the name Galbibacter pacificus sp. nov. is proposed. The type strain is CMA-7^T (=MCCC M28999^T = KCTC 92588^T). Moreover, the transfer of Joostella marina to the genus Galbibacter as Galbibacter orientalis nom. nov. (type strain En5^T = KCTC 12518^T = DSM 19592^T=CGMCC 1.6973^T) is also proposed.

Keywords: Galbibacter orientalis nom. nov; Galbibacter pacificus sp. nov; ocean surface seawater; polyphasic taxonomy; west Pacific Ocean.