Genome characterization and polyphasic taxonomy of strain IMCC14465, isolated by using dilution-to-extinction, beloning to the PS1 clade from the East Sea

초록

Culturing and characterization of marine bacterioplankton is crucial to understand physiology and the ecological roles of marine microorganisms. Although many isolates belonging to marine major phylogenetic groups have been successfully cultivated using the dilution-to-extinction method, there still remain many marine bacterial groups that have no cultured representatives. The PS1 clade in the class Alphaproteobacteria was recently identified in a study on metagenome sequences retrieved from the Pacific Ocean. Strain IMCC14465, belonged to PS1 clade was isolated from a surface seawater sample in the East Sea, Western Pacific Ocean, by dilution-to-extinction culturing. In this report, we present the phylogenetic analysis, phenotypic characterization, and genome property of strain IMCC14465, the first cultivated isolate of the PS1 clade. Strain IMCC14456 is a curved rod-shaped, non-flagellated, and strictly aerobic bacterium that does not form colonies on solid media. Temperature range for growth was 10-30 °C (optimum 25-30 °C). Predominant cellular fatty acids were C18:1 ω6c/C18:1 ω7c that are major fatty acids generally found in the Alphaproteobacteria. Cells of IMCC14456 showed activities for esculin hydrolysis and N-acetyl-β-glucosaminidase. The draft genome sequences of the strain were 1,929,044 nucleotides, with a G+C content of 47.4%. The genome of strain IMCC14465 was predicted to have complete gene sets for Enter-Doudoroff pathway, citric acid cycle, and gluconeogenesis. Also strain IMCC14465 contained a gene encoding proteorhodopsin (PR), a light-driven proton pump widely distributed in marine bacteria. In a light/dark growth experiment to determine an effect of proteorhodopsin, no significant difference in growth property was observed. The average nucleotide identity (ANI) value between strain IMCC14465 and RS24, the most closely related strain, was 80.5-83.5%, indicating they are separate genomic species.