Specific marine bacteria enhance the sexual reproduction and auxospore production of a marine diatom

Auxospore production is a sexual reproductive strategy by marine diatoms to re-attain normal size after the size-reducing effect of clonal reproduction. Here we investigated the influence of various marine bacterial groups on the sexual reproduction and auxospore production of the ubiquitous marine diatom, Odontella sp. We found that the marine diatom Odontella grown with Polaribacter and Cellulophaga (Bacteroidetes) and Pseudo-alteromonas (Gamma-proteobacteria) have significantly more cells undergoing sexual stages and auxosporilation than Odontella that is bacteria-free or co-cultured with other bacteria from Gamma-proteobacteria (Vibrio), Alphaproteobacteria (Sulfitobacter) or Firmicutes (Planococcus) group. Examination of the Odontella sp. microbiome composition indicated that 8% of its bacterial associates belong to Bacteroidetes group. The metabolite morphogen, indole acetic acid, released by the diatom bacterial associates are being compared along with the gene expression behind this specific interaction. Based from these physiological and genomic measurements, we conclude that specific bacterial microbiota are more mutualistic than others and may even be required by the diatom host to carry out the successful expression of important diatom-specific evolutionary trait, such as the production of auxospores that allow for size restitution and maintenance of genetic diversity in the Odontella population.