Isolation and genome analysis of bacteriophages infecting the SAR92 clade of marine gammaproteobacteria

초록

Isolation and characterization of phages infecting abundant marine bacteria are crucial for better taxonomic and functional interpretation of ever-increasing marine viral metagenomes. In this study, we isolated and characterized bacteriophages infecting the SAR92 clade, an abundant marine gammaproteobacterial group. The host strain IMCC15298 affiliated with the SAR92 clade within the family Porticoccaceae was isolated from the East Sea. A mixture of lytic bacteriophages infecting IMCC15298 was obtained from a coastal area of the Yellow Sea, through the enrichment culture. Attempts for pure isolation using serial dilution were unsuccessful. Observation using TEM showed that the phage mixture was dominated by a phage of the family Siphoviridae. Through genome sequencing by Illumina and Nanopore platforms, three bacteriophage genomes were assembled, which were named P15298-A (length: ~80 kb, G+C ratio: 40.9%), P15298-B (~59 kb, 45.8%), and P15298-C (~50 kb, 51.5%), respectively. All of the three phage genome sequences showed no or little similarity to previously cultured phage genomes, indicating the novelty of the isolated phages. Comparison with viral metagenomic contigs retrieved from diverse marine environments showed that P15298-A and P15298-C were similar to viral contigs from the Atlantic and Pacific Oceans, suggesting that these two phages represent widespread marine phage groups that have not been cultured so far. This study was the first to report bacteriophage that infects the abundant marine bacterial group SAR92 clade.