Dynamics in coastal RNA viruses and bacteriophages are driven by shifts in the community phylogenetic structure

Marine microbes including viruses are an essential part of the marine ecosystem that forms the base of the foodweb, and drives biogeochemical cycles. Marine viral communities display repeatable changes in abundance and community composition throughout time; however, whether these changes reflect shifts in dominance within evolutionarily related groups of viruses and their hosts is unexplored. To examine these dynamics, changes in the composition and phylogenetic makeup of two ecologically important groups of viruses, and their potential hosts, were sampled every two weeks for 13 months at a coastal site in British Columbia, Canada. Changes in the taxonomic composition within DNA bacteriophages related to T4-like viruses and marnavirus-like RNA viruses infecting eukaryotic phytoplankton, as well as bacteria and eukaryotes, were examined using amplicon sequencing of gene fragments encoding the major capsid protein ( gp23 ), the RNA-dependent RNA polymerase ( RdRp ) and the 16S and 18S ribosomes, respectively. The results showed that for both viral marker genes, the dominant groups of phylogenetically-related viruses shifted over time and contained many transient taxa and few persistent taxa; yet, different community structures were observed in these different viral communities. Additionally, with strong lagged correlations between viral richness and community similarity of putative hosts, the results imply that viruses influence the composition of the host communities.