Mode of resistance to viral lysis affects host growth across multiple environments in the marine picoeukaryote Ostreococcus tauri.

Viruses play important roles in population dynamics and as drivers of evolution in single-celled marine phytoplankton. Viral infection of Ostreococcus tauri often causes cell lysis, but two spontaneously arising resistance mechanisms occur: resistant cells that cannot become infected and resistant producer cells that are infected but not lysed, and which may slowly release viruses. As of yet, little is known about how consistent the effects of viruses on their hosts are across different environments. To measure the effect of host resistance on host growth, and to determine whether this effect is environmentally dependent, we compared the growth and survival of susceptible, resistant and resistant producer O. tauri cells under five environmental conditions with and without exposure to O. tauri virus. While the effects of exposure to virus on growth rates did not show a consistent pattern in populations of resistant cells, there were several cases where exposure to virus affected growth in resistant hosts, sometimes positively. In the absence of virus, there was no detectable cost of resistance in any environment, as measured by growth rate. In fact, the opposite was the case, with populations of resistant producer cells having the highest growth rates across four of the five environments.