Facilibium subflavum gen. nov., sp. nov. and Cysteiniphilum halobium sp. nov., new members of the family Fastidiosibacteraceae isolated from coastal seawater

Abstract

Two Francisella-like bacteria, designated strains SYSU SYW-5T and SYSU SYW-6T, were isolated from coastal seawater sampled at Huizhou Double-Moon Bay, Guangdong Province, PR China. Cells were found to be Gram-stain-negative, non-motile, non-spore-forming and of pleomorphic shape (coccobacilli or rod). Chemotaxonomic analysis of the plasma membrane revealed ubiquinone-8 as the respiratory quinone, and saturated branched-chain (anteiso-C15 : 0) and saturated straight-chain (C18 : 0) fatty acids as major components (>8 % of total fatty acid). The major polar lipids comprised diphosphatidylglycerol (cardiolipin), phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine, as well as an unidentified aminophospholipid and an unidentified phospholipid in SYSU SYW-5T, and two unknown polar lipids in SYSU SYW-6T. Comparison of 16S rRNA gene sequences showed that SYSU SYW-5T had maximum similarity to Fastidiosibacter lacustris SYSU HZH-2T (93.4 %), while SYSU SYW-6Thad maximum similarity to Cysteiniphilum litorale SYSU D3-2T (97.5 %). Phylogenetic dendrograms based on 16S rRNA genes and 31 concatenated protein markers revealed that the two novel strains represent a distinct lineage within the family Fastidiosibacteraceae. The average nucleotide identity and in silico DNA-DNA hybridization values between the two isolates and their related species were well below the threshold limit for species delineation (<89.2 and <35 %, respectively). Based on the above results, strain SYSU SYW-5T is proposed to be a novel species of a new genus with the name Facilibium subflavum gen. nov., sp. nov. (SYSU SYW-5T = DSM 103991T= KCTC 52556T), and strain SYSU SYW-6T is proposed to be a novel species of genus Cysteiniphilum with the name Cysteiniphilumhalobium sp. nov. (SYSU SYW-6T=DSM 103992T=KCTC 52558T).