C.-E. T. Chow

The temporal community dynamics and persistence of different viral types in the marine environment are still mostly obscure. Polymorphism of the major capsid protein gene, g23, was used to investigate the community composition dynamics of T4-like myoviruses in a North Atlantic fjord for a period of 2 years. A total of 160 unique operational taxonomic units (OTUs) were identified by terminal restriction fragment length polymorphism (TRFLP) of the gene g23. Three major community profiles were identified (winter-spring, summer, and autumn), which resulted in a clear seasonal succession pattern. These seasonal transitions were recurrent over the 2 years and significantly correlated with progression of seawater temperature, Synechococcus abundance, and turbidity. The appearance of the autumn viral communities was concomitant with the occurrence of prominent Synechococcus blooms. As a whole, we found a highly dynamic T4-like viral community with strong seasonality and recurrence patterns. These communities were unexpectedly dominated by a group of persistently abundant viruses.

Abstract Over two decades of research have indicated that viruses play crucial roles in aquatic food webs as active constituents of the microbial loop and in the population ecology of both prokaryotic and eukaryotic microorganisms. Over the past 5 years, there has been a sharp increase in reported aquatic virus research, notably in the areas of freshwater viral ecology, viruses of eukaryotic microorganisms and viral genetic diversity. Recent studies of the interactions between viral infection, bacterivory and grazing have demonstrated the complex dynamics of viral infection within aquatic ecosystems. These reports have helped solidify our understanding of the environmental controls on viral abundance, impacts of viral infection upon host community structure and have elucidated new roles of viruses in biogeochemical cycles – such as photosystem gene expression. Previously unrecognised groups of viruses ( ribonucleic acid viruses and single‐stranded deoxyribonucleic acid viruses) have also been revealed as diverse and active components of marine virioplankton assemblages. Key Concepts: Viruses are the most numerically dominant organisms on earth, and their abundance varies between habitats, often according to local primary productivity. Both viral activity and bacterivory contribute significantly to bacterial mortality in aquatic ecosystems, which in turn influence global‐scale biogeochemical cycles. Methodological advances, such as metagenomics and genomics, have greatly facilitated studies of marine viruses and resulted in key discoveries on viral diversity, viral–host gene transfer and viral influence on host cell physiology. Photosystem genes are common in cyanophage and are hypothesised to enhance viral production rates. Viral‐induced mortality may be a key factor in controlling or terminating algal blooms.