A novel strain of a member of the family Alteromonadaceae was isolated from the phycosphere of a diatom and designated as LMIT007T. LMIT007T could form milk-white, opaque, circular and smooth colonies on 2216E marine agar. LMIT007T cells were around 1.0-1.8 µm long, 0.8-1.8 µm wide, round or oval shaped and had polar flagella but were non-motile. Optimum conditions for growth were 25 °C, pH 7.0 and 6 % (w/v) NaCl. The results of 16S rRNA gene-based analysis indicated that LMIT007T had the highest similarity with the type strains Aestuaribacter halophilus JC2043T (95.95 %), Alteromonas lipolytica JW12T (95.60 %) and Alteromonas halophila KCTC 22164T (94.21 %). Furthermore, the results of phylogenetic analysis based on 16S rRNA gene sequences and of phylogenomic analysis indicated that LMIT007T could be clustered into the family Alteromonadaceae but formed a separate branch. The genome size of the strain was 2.95 Mbp and the DNA G+C content was 41.6 %. The average nucleotide identity (ANI) values of orthologous genes between LMIT007T and species of other closely related genera within the family Alteromonadaceae ranged from 66.9 to 69.2 %, and the average amino acid identity (AAI) values ranged from 60.0 to 65.7 %. The main respiratory quinone was ubiquinone-8. The major fatty acids were summed feature 3 (C16 : 1ω7c / C16 : 1ω6c) and C16 : 0. The polar lipid profile contain phosphatidylethanolamine, phosphatidylglycerol, aminolipid, two phospholipid and an unknown polar lipid. On the basis of the results of the polyphasic analysis, strain LMIT007T is suggested to represent a novel genus and species within the family Alteromonadaceae, for which the name Opacimonas viscosa gen. nov., sp. nov. is proposed. The type strain is LMIT007T (=MCCC 1K08161T=KCTC 92597T).
Keywords: Opacimonas; genome reduction; phycosphere; polyphasic analysis.