Resource dynamics during infection of Micromonas pusilla by virus MpV‐Sp1

Abstract

Viruses infecting marine phytoplankton drive phytoplankton diversity, terminate blooms and shuttle genetic material. Assessments of the scale of viral impacts on trophic networks are, however, speculative. We investigated fluxes of DNA between host and virus during infection of the prasinophyte alga Micromonas pusilla by phycodnavirus MpV SP1. Under a light-dark regimen, viral genomes accumulated to a transient peak within 24 h, at the expense of both host DNA synthesis and nuclear DNA. Viral genome abundance then declined soon after host lysis. This release of a phosphate-rich nucleotide pool during viral infection of phytoplankton should be considered in trophic models. Lysis required light and was stalled in darkness, meanwhile viral genome replication proceeded slowly in the dark. Viral exploitation of this host is therefore only partially light-dependent and infected phytoplankton are poised to lyse at dawn or if mixed to the photic zone. The chloroplast genome remained intact until lysis, indicating that either this DNA pool is inaccessible or the virus spares the chloroplast for its energy and reductant generation. The photochemical turnover of residual Photosystem II complexes accelerated during lysis, indicating that events in late infection heighten demands on the remaining host photosynthetic systems, consistent with the light dependency of lysis.

Elevated CO 2 and Phosphate Limitation Favor Micromonas pusilla through Stimulated Growth and Reduced Viral Impact

“…It has been proposed that viral replication is particularly sensitive to P limitation due to the relatively low C:P ratio of viruses (18). Brown and colleagues (66) showed an apparent utilization of the host genome by MpV for DNA synthesis, strengthening the idea that viral replication is indeed rate limited by substrate. However, MpV replication has been found to halt in the dark (21,66).…”

Temperature is a key factor in Micromonas–virus interactions

“…Several studies pointed out the similarity of photoacclimation trends at low temperatures to those at high irradiance (Anning et al, 2001;El-Sabaawi and Harrison, 2006;Claquin et al, 2008). Reports on the effect of light intensity evidenced the importance of this factor in regulating algal host-virus interactions (Waters and Chan, 1982;Bratbak et al, 1998;Brown et al, 2007;Baudoux and Brussaard, 2008). However, elevated irradiance per se did not appear to alter viral infection of Micromonas (Baudoux and Brussaard, 2008).…”

Diversity of Viruses Infecting the Green Microalga Ostreococcus lucimarinus

“…Such a metabolic stimulation of viral fitness has been described in cyanobacteria, wherein the host is supplemented with proteins involved in photosynthesis (60). In the closely related prasinophyte Micromonas, the virus appears to spare the chloroplast, allowing it to maintain energy production and the photochemical turnover of residual photosystem II complexes during lysis (61). However, in OlVs most of these specific genes have unknown functions, making it more difficult to speculate on possible adaptive functions.…”