Isolation and Genomic Characterization of Bacteriophages Infecting the SAR92 Clade, an Abundant Oligotrophic Marine Gammaproteobacterial Group

초록

Bacteriophages (phages) are the most abundant biological entities in marine environments and have huge effects on bacterial community and biogeochemical cycles. Although the recent deluge of marine viral metagenomics data has shown enormous diversity of marine phages, biological interpretation of those data requires experimental characterization of phage-host systems of abundant marine bacterial groups. In this study, we report on the first isolation of bacteriophages that infect the SAR92 group, an abundant oligotrophic marine gammaproteobacterial group. The host bacterial strain, IMCC15298, was obtained from the East Sea by high-throughput culturing and was found to belong to the SAR92 group of the family Porticoccaceae. A mixed culture of bacteriophages infecting IMCC15298 lytically was isolated from a coastal seawater sample collected in the Yellow Sea. Morphological characterization by TEM showed that the culture was dominated by a phage of the family Siphoviridae. Three complete genomes, with lengths of ~80, 89, and 59 kb, were obtained by Illumina and Nanopore sequencing. More than 90% of sequencing reads were mapped to the ~80 kb genome, with many polymorphic sites, indicating that this genome sequence represents a major phage population (of the mixed culture) encompassing several very closely related phage strains. [This study was supported by a grant from the Marine Biotechnology Program, funded by the Ministry of Oceans and Fisheries, Korea.]