Biofilm interactions—bacteria modulate sexual reproduction success of the diatom Seminavis robusta

Marine biofilms are complex multi-species communities where chemical signaling regulates a substantial share of interactions. The involved natural products represent targets for competition strategies by signal interference. Diatoms, that often dominate biofilms, rely on a complex pheromone system during sexual reproduction, involving synchronizing and attracting metabolites. The present study addresses the effect of bacteria on sexual reproduction of the model pennate diatom Seminavis robusta. We observe that sexual reproduction is most efficient under axenic conditions. Bacteria isolated from field collected biofilms modulate sexual reproduction in the algae. A species-specific effect on the diatom mating efficiency could be observed, with Maribacter sp. and Marinobacter sp. significantly reducing the sexual reproduction rate. Spent medium from these bacteria has the same effect, demonstrating that chemically mediated cross kingdom interactions take place. In contrast, proportion of auxospores. We further observed a lower concentration of the diatom attraction pheromone diproline in the presence of bacteria compared to axenic conditions. In agreement, the Seminavis-associated bacterial community as well as isolated bacterial strains degraded the pheromone over time. Our results highlight that the pheromone system of diatoms is subject to interference strategies of the associated bacterial community by modulation of the signal landscape