Abstract
ABSTRACTThe ecology of viruses has been studied only in a limited number of rivers and streams. In light of a recent re‐appraisal of the global fluvial surface area, issues such as abundance and production, host mortality and the influence of suspended particles and biofilms are addressed. Viral life cycles, potential impacts of viruses on water biochemistry and carbon flow, and viral diversity are considered. Variability in trophic levels along with the heterogeneous nature and hydrological dynamics of fluvial environments suggest a prevailingly physical control of virus‐related processes under lotic conditions and more biological control under lentic conditions. Viral lysis likely contributes to a pool of rapidly cycling carbon in environments typically characterized by high proportions of recalcitrant terrestrial carbon. On average, 33.6% (equalling 0.605 Pg C year−1) of the globally respired carbon from fluvial systems may pass through a viral loop. Virus distribution and the proportion of organic material in horizontal transport versus processes in retention zones remain to be determined in detail. The need for up‐scaling the contribution of virus‐related processes in fluvial systems is of global relevance. Further, the role of climate change and the effect of anthropogenic alterations of fluvial systems on viruses require attention. The identification of these considerable knowledge gaps should foster future research efforts.
Highlights
The ecology of viruses has been studied only in a limited number of rivers and streams
The typically high frequency of virus infection in oceanic ecosystems is known to be a major cause of prokaryotic host mortality
The current review paper provides: (i) an overview of existing information on virus ecology in fluvial waters by tackling issues such as virus-mediated microbial host mortality, viral lifestyles and mechanisms controlling viral activity; (ii) an assessment of the impact of variable hydrology and the role of suspended particles and biofilms on viruses; (iii) information on the need to investigate horizontal transport processes of virus-related solutes and particles, and virus dissemination; and (iv) arguments for the necessity of up-scaling the contribution of virus-related processes, for example their potential contribution to global CO2 outgassing and the role of climate change on these contributions. These considerations include the significance of anthropogenic alterations of fluvial systems and, together, will help define research fields for future studies
Summary
As in the marine environment, in inland aquatic systems viral infection of both auto- and heterotrophic bacteria and subsequent lysis of host cells is responsible for a considerable proportion of prokaryotic mortality (Peduzzi & Luef, 2009). Even though the various methods for assessing this are subject to bias from many sources, in aquatic systems (both marine and freshwater) typically 10–20% of bacterial production is lost due to virus infection (Jacquet et al, 2010) When prokaryotes, such as cyanobacteria, are important members of the food chain, their lysis can have adverse effects even for vertebrate end-consumers (Peduzzi et al, 2014). There is still no standard approach for estimating and comparing mortality in prokaryotic and eukaryotic communities that can be attributed to viruses in different aquatic environments This prevents the accurate integration of virus-related mortality into overall models (Jacquet et al, 2010), for riverine systems
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