Abstract
SummaryIn marine ecosystems, viruses are major disrupters of the direct flow of carbon and nutrients to higher trophic levels. Although the genetic diversity of several eukaryotic phytoplankton virus groups has been characterized, their infection dynamics are less understood, such that the physiological and ecological implications of their diversity remain unclear. We compared genomes and infection phenotypes of the two most closely related cultured phycodnaviruses infecting the widespread picoprasinophyte Ostreococcus lucimarinus under standard‐ (1.3 divisions per day) and limited‐light (0.41 divisions per day) nutrient replete conditions. OlV7 infection caused early arrest of the host cell cycle, coinciding with a significantly higher proportion of infected cells than OlV1‐amended treatments, regardless of host growth rate. OlV7 treatments showed a near‐50‐fold increase of progeny virions at the higher host growth rate, contrasting with OlV1's 16‐fold increase. However, production of OlV7 virions was more sensitive than OlV1 production to reduced host growth rate, suggesting fitness trade‐offs between infection efficiency and resilience to host physiology. Moreover, although organic matter released from OlV1‐ and OlV7‐infected hosts had broadly similar chemical composition, some distinct molecular signatures were observed. Collectively, these results suggest that current views on viral relatedness through marker and core gene analyses underplay operational divergence and consequences for host ecology.
Highlights
The structure and function of marine ecosystems are profoundly influenced by the activity of viruses
Viral infection and lysis of specific bacterial host genotypes leads to changes in the size and genetic makeup of host populations and appear to represent a significant selective pressure driving host evolution as well, difficult to confirm in the marine environment (Martiny et al, 2014; Thingstad et al, 2014)
Their genomes are similar in size to previous estimates, and the genome sequences were nearly identical to the previous genome assemblies
Summary
The structure and function of marine ecosystems are profoundly influenced by the activity of viruses. The consequences of viral infection at the population level are generally considered to scale up to influence community composition and nutrient availability to the broader community via lysis products and/or changes in host metabolism (Fuhrman, 1999; Suttle, 2007; Weitz and Wilhelm, 2012; Hamblin et al, 2014; Ma et al, 2018). The general ecological importance of marine phytoplankton (both eukaryotic and cyanobacterial) and their viruses is widely recognized (e.g., Middelboe and Brussaard, 2017), many fundamental first-order questions persist about how viruses interact with phytoplankton hosts, how host physiology impacts viral production and how these factors impact broader biogeochemical cycles (Brum and Sullivan, 2015; Breitbart et al, 2018; Horas et al, 2018)
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