Metabolites from intact phage-infected Synechococcus chemotactically attract heterotrophic marine bacteria.

Chemical cues mediate interactions between marine phytoplankton and bacteria, underpinning ecosystem-scale processes including nutrient cycling and carbon fixation. Phage infection alters host metabolism, stimulating the release of chemical cues from intact plankton, but how these dynamics impact ecology and biogeochemistry is poorly understood. Here we determine the impact of phage infection on dissolved metabolite pools from marine cyanobacteria and the subsequent chemotactic response of heterotrophic bacteria using time-resolved metabolomics and microfluidics. Metabolites released from intact, phage-infected Synechococcus elicited strong chemoattraction from Vibrio alginolyticus and Pseudoalteromonas haloplanktis, especially during early infection stages. Sustained bacterial chemotaxis occurred towards live-infected Synechococcus, contrasted by no discernible chemotaxis towards uninfected cyanobacteria. High-throughput microfluidics identified 5'-deoxyadenosine and 5'-methylthioadenosine as key attractants. Our findings establish that, before lysis, phage-infected picophytoplankton release compounds that attract motile heterotrophic bacteria, suggesting a mechanism for resource transfer that might impact carbon and nutrient fluxes across trophic levels.