Synergy in viral-bacterial co-infection expedites algal bloom demise.

Alteromonas bacteria drive viral-bacterial synergy that significantly enhances virus-induced algal mortality in Gephyrocapsa huxleyi and three other microalgae, accelerating bloom demise.

• Why it matters: Bloom collapse is synchronous, yet fewer than 30% of algal cells are actively infected by viruses, implying additional mortality agents beyond viruses alone.
• What they did: In a synthetic community of Gephyrocapsa huxleyi, bacteria, and bloom-derived viruses, the study quantified tripartite interactions using a synergy index and a benefit index to assess interaction strength and bacterial fitness.
• The result: Alteromonas showed consistently high synergy and benefit indices, chemoattracted to infected cell extracts, accumulated in bloom-demise aggregates, and increased during oceanic bloom collapse, indicating viral-bacterial synergy as a mortality agent controlling bloom termination.

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