Phenotypic and Genomic Characteristics of Three Freshwater Bacterial Strains Constituting a New Subcluster of Genus Polynucleobacter

초록

The genus Polynucleobacter is ubiquitous in freshwater environments. Polynucleobacter strains cultured so far have been grouped into four subclusters based on 16S rRNA gene sequence divergence: subclusters PnecA, B, C and D. We report here preliminary analyses on phenotypic and genomic characteristics of Polynucleobacter strains IMCC29146, IMCC30063T, and IMCC30228 that are not affiliated with any of the four previously-known subclusters. The three strains were isolated from Lake Soyang, an oligotrophic freshwater reservoir, by dilution-to-extinction culturing. Phylogenetic analyses showed that these strains clearly formed a new distinct subcluster within genus Polynucleobacter. All three strains were aerobic, facultatively anaerobic, catalase- and oxidase-positive, and non-motile. Growth of strains occurred on R2A and NSY medium at 10?30°C (optimum, 20°C) with 0?0.5% NaCl (optimum, 0%). The predominant fatty acids were C16:0 (32.17?37.03%), C17:0 cyclo (11.91?26.79%), and feature 3 including C16:1 ω6c and/or C16:1 ω7c (17.59?30.68%). The draft genome sequences of the strains showed a length of 2.4?2.5 Mb and an average G+C content of 44.5?44.8%. Genes for polyhydroxyalkanoate (PHA) were predicted from the genomes, which was consistent with PHA granules in cultured cells observed using transmission electron microscopy. [This study was supported by a grant of the Mid-Career Research Program through the NRF.]