Environmental bacteriophages: viruses of microbes in aquatic ecosystems

Abstract

Since the discovery 2–3 decades ago that viruses of microbes are abundant in marine ecosystems, viral ecology has grown increasingly to reach the status of a full scientific discipline in environmental sciences. A dedicated ISVM society, the International Society for Viruses of Microorganisms, (http://www.isvm.org/) was recently launched. Increasing studies in viral ecology are sources of novel knowledge related to the biodiversity of living things, the functioning of ecosystems, and the evolution of the cellular world. This is because viruses are perhaps the most diverse, abundant, and ubiquitous biological entities in the biosphere, although local environmental conditions enrich for certain viral types through selective pressure. They exhibit various lifestyles that intimately depend on the deep-cellular mechanisms, and are ultimately replicated by members of all three domains of cellular life (Bacteria, Eukarya, Archaea), as well as by giant viruses of some eukaryotic cells. This establishes viral parasites as microbial killers but also as cell partners or metabolic manipulators in microbial ecology. The present chapter sought to review the literature on the diversity and functional roles of viruses of microbes in environmental microbiology, focusing primarily on prokaryotic viruses (i.e., phages) in aquatic ecosystems, which form the bulk of our knowledge in modern environmental viral ecology.

Viral dynamics in two trophically different areas in the Central Adriatic Sea

“…A similar pattern was observed in the Northern Adriatic [13,21,22,50]. It is known that viral and bacterial abundances change according to the productivity of the aquatic environment [7]. A higher abundance of marine bacteria is usually followed by a higher abundance of marine viruses, and thus, viral production [6].…”

“…Viruses lyse 10-50% of bacterial standing stock per day on average [5]. This value can be even higher, depending mostly on the host density and productivity, but also on environmental conditions, such as temperature, salinity and UV radiation [3,4,6,7]. Additionally, virus-mediated bacterial mortality can even match grazer-mediated mortality in different marine environments [6,8].…”

Diversity of Viruses Infecting the Green Microalga Ostreococcus lucimarinus

“…The particles also are morphologically similar to the much larger (165 to 190 nm) Chlorella viruses except for the spike structure at the vertex, which is not observed in prasinoviruses (45,48). Globally, they show icosahedral symmetry, like the great majority of the other dsDNA aquatic eukaryote viruses currently described (49), without any tail, in contrast to many archaeal and bacterial bacteriophages (50,51). The size of their genomes (around 200 kb) and the number of potential ORFs also are similar to those of the other sequenced prasinoviruses (17)(18)(19)(20).…”

Bacterial-viral interactions in the sea surface microlayer of a black carbon-dominated tropical coastal ecosystem (Halong Bay, Vietnam)

“…affecting bacterioplankton dynamics can translate to major effects on other constituents of the planktonic food web, and thus on the structure of the entire ecosystem. The fact that viruses (primarily bacteriophages) regulate bacterial growth and metabolism by their destructive action of 20-50% of daily bacterial production (Suttle, 2005;Sime-Ngando, 2014) makes viruses an additional important influence on biogeochemical processes and energy fluxes, structuring food web dynamics and governing microbial diversity in aquatic systems (Breitbart, 2012;Sime-Ngando, 2014;Fuhrman et al, 2015). Although the effect of BC on climate has been widely studied (e.g., Ramanathan and Carmichael, 2008), our understanding of the direct and indirect effects of BC on bacteria-virus interactions and the processes they mediate in aquatic ecosystems is still in its infancy.…”