Viral infection of coccolithophore host induces shifts in particulate organic matter stoichiometry

Blooms of the coccolithophore Gephyrocapsa huxleyi (formerly Emiliania huxleyi) are routinely infected by a specific lytic virus (EhV) that kills host cells and drives bloom termination. However, the impact of EhV on nutrient retention and stoichiometric ratios of particulate organic matter remains unknown, limiting our current understanding of the biogeochemical significance of the G. huxleyi–EhV interaction. To tackle this knowledge gap, we surveyed both nitrate, phosphate, and alkalinity consumption by the cells, as well as the elemental composition (C : N : P) of particulate organic matter during infections in culture. We found that within 24 h of infection, alkalinity concentration in the solution stabilized, and nutrient uptake declined to low levels. In parallel, the molar ratio of carbon to nitrogen in particulate organic matter increased by 10–17% and the nitrogen to phosphorus ratio declined by 5–12% relative to the noninfected algal cultures. These variations likely resulted from intracellular lipid accumulation as part of viral infection as well as the differential retention of phosphorus-rich macromolecular pools in decaying cells, respectively. After infection, as most host cells lysed, we detected a progressive enrichment in phosphorus and nitrogen relative to carbon in the remaining particulate organic matter, which could be attributed to the accumulation of colonizing heterotrophic bacteria with a distinct elemental composition. This study indicate that marine viruses influence the elemental stoichiometry and fate of phytoplankton-born organic materials in the oceans.