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

Two Francisella -like bacteria, designated strains SYSU SYW-5 T and SYSU SYW-6 T , 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-C 15 : 0 ) and saturated straight-chain (C 18 : 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-5 T , and two unknown polar lipids in SYSU SYW-6 T . Comparison of 16S rRNA gene sequences showed that SYSU SYW-5 T had maximum similarity to Fastidiosibacter lacustris SYSU HZH-2 T (93.4 %), while SYSU SYW-6 T had maximum similarity to Cysteiniphilum litorale SYSU D3-2 T (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-5 T is proposed to be a novel species of a new genus with the name Facilibium subflavum gen. nov., sp. nov. (SYSU SYW-5 T = DSM 103991 T = KCTC 52556 T ), and strain SYSU SYW-6 T is proposed to be a novel species of genus Cysteiniphilum with the name Cysteiniphilumhalobium sp. nov. (SYSU SYW-6 T =DSM 103992 T =KCTC 52558 T ).