Algal Betaine Triggers Bacterial Hydrogen Peroxide Production that Promotes Algal Demise

Abstract

Hydrogen peroxide (H2O2) plays various roles in the ocean, acting as a signaling molecule at low concentrations and causing oxidative stress when accumulated. While many marine microbes produce H2O2, its role in microbial interactions remains unclear. Here, we used transcriptomics, genetics, and metabolomics to study H2O2 dynamics in the interaction between Emiliania huxleyi algae and Phaeobacter inhibens bacteria. We found that H2O2 levels rise during algal death and that bacterial H2O2 production triggers this demise. Manipulating H2O2 levels shifted the outcome of the interaction. We also uncovered a link between H2O2 and betaine metabolism: aging algae release betaine, which promotes bacterial H2O2 production and, in turn, accelerates algal death. Genes involved in H2O2 and betaine metabolism were upregulated in environmental samples from an algal bloom. Together, our findings identify H2O2 and betaine as key molecules that modulate algal-bacterial interactions, potentially impacting microbial dynamics in marine ecosystems.