Congregibacter variabilis sp. nov. and Congregibacter brevis sp. nov. Within the OM60/NOR5 Clade, Isolated from Seawater, and Emended Description of the Genus Congregibacter.

Abstract

Two Gram-stain-negative, aerobic, motile by means of flagella, short rod-shaped bacterial strains, designated IMCC43200^T and IMCC45268^T, were isolated from coastal seawater samples collected from the South Sea of Korea. Strains IMCC43200^T and IMCC45268^T shared 98.6% 16S rRNA gene sequence similarity and were closely related to Congregibacter litoralis KT71^T (98.8% and 98.7%, respectively). Complete whole-genome sequences of IMCC43200^T and IMCC45268^T were 3.93 and 3.86 Mb in size with DNA G + C contents of 54.8% and 54.2%, respectively. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains were 74.5% and 23.4%, respectively, revealing that they are independent species. The two strains showed ANI values of ≤ 75.8% and dDDH values of ≤ 23.0% to the type and only species of the genus Congregibacter (C. litoralis), indicating that each strain represents a novel species. Both strains contained summed feature 3 (comprising C_16:1 ω6c and/or C_16:1 ω7c) and summed feature 8 (comprising C_18:1 ω6c and/or C_18:1 ω7c) as major fatty acid constituents. The predominant isoprenoid quinone detected in both strains was ubiquinone-8 (Q-8). The major polar lipids of the two strains were phosphatidylethanolamine, phosphatidylglycerol, phospholipids, and aminolipids. Based on the phylogenetic, genomic, and phenotypic characterization, strains IMCC43200^T and IMCC45268^T were considered to represent two novel species within the genus Congregibacter, for which the names Congregibacter variabilis sp. nov. and Congregibacter brevis sp. nov. are proposed with IMCC43200^T (= KCTC 8133^T = NBRC 116295^T = CCTCC AB 2023139^T) and IMCC45268^T (= KCTC 92921^T = NBRC 116135^T) as the type strains, respectively.