Viral assemblage variation in an Arctic shelf seafloor

Abstract

Spatial differences in microbial communities are observable even in habitats with moderate environmental variation, such as within the pelagic zone or seafloor of geographically finite regions of the oceans. Here we explore whether biogeographical variations are also manifested at this level in the structure of viral assemblages by comparing DNA viromes from the Barents Sea upper seafloor, collected at 5 geographically separated locations. Of the open reading frames, 27 to 44% showed significant similarity to genes of viral genomes in the Refseq database. The majority of the identified open reading frames, i.e. 86 to 95%, were affiliated with sequences of single-stranded DNA (ssDNA) viruses, but the ssDNA virus genetic material was likely strongly overrepresented due to the use of phi29 DNA polymerase for amplifying viral DNA. The majority of ssDNA virus sequences originated from the Microviridae family of phages and the eukaryotic Circular Rep-encoding ssDNA (CRESS-DNA) viruses. The sediment virus assemblages showed higher overall similarity to counterparts from deep-sea sediment of the Pacific Ocean than to, e.g., Arctic Ocean pelagic viromes, supporting the presence of common compositional features in sediment viral assemblages across continental-scale geographical separations. The Barents Sea viromes grouped biogeographically in accordance with the south-north environmental division of this Arctic sea by the oceanic polar front, thereby mirroring a corresponding 16S rRNA gene-based biogeographical division of the bacterial communities. However, compositional differences in the eukaryotic virus assemblages rather than the bacteriophages appeared to be the primary basis for this spatial separation.