Taming the Unrecognized Phages from Aquatic Ecosystems

초록

Viruses, obligate parasites, are the smallest and the most abundant biological entities, which thrive on earth with approximately 1031 particles. Most viruses in the ecosystem are believed to be bacteriophages (phages) that are particularly found in aquatic environments where phage particles can encounter their host cells while freely floating. Therefore, diverse researches on phages have been specifically performed in marine environment, the largest reservoir for phage particles, such as isolation of the most abundant marine bacteriophages, pelagiphages and Puniceispirillum phage HMO-2011 and a verrucophage known to infect the phylum Verrucomicrobia. These successful stories tell us that cultivation of major prokaryotic strains are prerequisite for taming marine viruses since the cultivation of bacterial and archaeal strains is the only way of isolating viruses that infect prokaryotic cells. On the contrary, freshwater bacteriophages have been understudied, representing that only few of freshwater cyanophages have been identified and the rest of the phages remain largely unknown. Therefore, both the bird’s eye view (virome analyses) and microscopic view (individual phages) for freshwater phages are in need. First, in order to investigate the viral community distribution, we have performed viral metagenomic studies on an oligotrophic lake. Most of the contigs obtained from the virome study revealed to be most closely related to marine-origin bacteriophages, which indicated the lack of identified freshwater phages, leading to limited interpretation of freshwater viral community. Second, along with the viral metagenome analyses, we have isolated novel freshwater bacteriophages from the same freshwater lake.