Taxonomically distinct diatom viruses differentially impact microbial processing of organic matter

Phytoplankton viruses facilitate the production of dissolved organic matter (DOM) through host lysis, shaping DOM composition, and subsequent regenerative processing. We explored how DOM generated from a bloom-forming, centric diatom, infected with taxonomically distinct viruses—a single-stranded (ss) DNA and a ssRNA virus—impacted microbial processing of organic matter. DOM derived from uninfected and ssDNA virus–infected cultures supported growth in bacterial isolates and a mixed assemblage. In contrast, DOM from ssRNA virus infection did not stimulate growth, but rather induced ectoproteolytic activity, suggesting this DOM was less bioavailable. Exoprotease activity was also substantially higher in ssRNA virus–infected cellular exudates compared to ssDNA virus–infected and uninfected cultures. This suggests that DOM produced through virus-mediated host lysis does not a priori support secondary production and implicate ssRNA virus infection as a source of proteolytic activity in the water column, highlighting a multifaceted role for viruses in altering microbial utilization and remineralization length scales of organic matter in the ocean.