Three Phages from a Boreal Lake during Ice Cover Infecting Xylophilus, Caulobacter, and Polaromonas Species

Abstract

Although the important role of microbes in freshwater is well understood, studies on phage–host systems in such environments during ice cover are completely lacking. Here, we describe the isolation and characterization of three new bacteriophages infecting Xylophilus sp., Caudobacter sp., and Polaromonas sp. from freshwater samples taken under the ice cover of Lake Konnevesi, Finland. Lumi, Kuura, and Tiera bacteriophages have tailed icosahedral virions and double-stranded DNA. Lumi is a siphophage with a genome of 80,496 bp, and Kuura and Tiera are podophages, and their genomes are 43,205 and 45,327 bp in length, resembling viruses in the class Caudoviricetes. Their host ranges were very limited among the winter-isolated bacterial strains from Konnevesi, each infecting only their own hosts. They can infect efficiently at 4 °C, showing that they are adapted to living in lake water under ice cover. Analysis of the viral genome sequences showed that a significant number of the gene products of each virus are unique, indicating that there is unexplored viral diversity in freshwaters. To our knowledge, Lumi and Tiera are the first phages isolated on the Xylophilus sp. and Polaromonas sp. strains, allowing their exploitation in further studies of freshwater bacterial–phage interactions.

Arctic bacterial diversity and connectivity in the coastal margin of the Last Ice Area

“…Phylotype pol1, which was the most abundant member of the Polaromonas genus in Thores, was also ubiquitous. This phylotype was closely related to P. ginsengisoli , which was initially isolated from soil, and shares 98.6% of its 16 S rRNA with P. eurypsychrophila [ 55 ], but has since been identified in other systems, including in the water column of a boreal lake during winter [ 56 ]. The consistent presence of these two phylotypes (pol1, pol2) across the watershed suggests these members of the Polaromonas genus are generalists with broad tolerances that likely endure year-to-year, as data presented here were collected over two consecutive summers.…”