High diversity and potential origins of T4-type bacteriophages on the surface of Arctic glaciers.

Tailed bacteriophages are the most abundant viruses in the biosphere. Here we examined the T4-type bacteriophage community inhabiting the surface of two glaciers in Svalbard. We used a molecular approach to target g23, the major capsid protein gene, to demonstrate that in the extreme cryoconite hole habitats the T4-type phages are surprisingly diverse. Phylogenetic analysis revealed that cryoconite hole sediments harbour a mixed phage community spanning multiple T4-type phage subgroups. The majority (71 %) of phage sequences clustered into three novel phylogenetically distinct groups, whilst the remainder clustered with known marine and soil derived phage sequences. The meltwater in cryoconite holes also contained a further distinct phage community which was related to previously detected marine phage variants. The ability of phages to move between marine and glacial habitats was tested in a transplantation experiment. Phages from the nearby marine fjord were found to be capable of initiating infection of supraglacial bacteria, suggesting suitable hosts could be found by non-native phages. Together this evidence suggests that the surface of glaciers contain both novel and cosmopolitan phages, some of which may have arrived in the cryosphere from other biomes.