Response of diatom-associated bacteria to host growth state, nutrient concentrations, and viral host infection in a...

Diatoms are photosynthetic unicellular eukaryotes found ubiquitously in aquatic systems. Frequent physical associations with other microorganisms such as bacteria may influence diatom fitness. The predictability of bacterial-diatom interactions is hypothesized to depend on availability of nutrients as well as the physiological state of the host. Biotic and abiotic factors such as nutrient levels, host growth stage and host viral infection were manipulated to determine their effect on the ecological succession of bacterial communities associated with a single cell line of Chaetoceros sp. KBDT20; this was assessed using the relative abundance of bacterial phylotypes based on 16S rDNA sequences. A single bacterial family, Alteromonadaceae, dominated the attached-bacterial community (84.0%), with the most prevalent phylotypes belonging to the Alteromonas and Marinobacter genera. The taxa comprising the other 16% of the attached bacterial assemblage include Alphaproteobacteria, Betaproteobacteria, Bacilli, Deltaproteobacteria, other Gammaproteobacteria and Flavobacteria. Nutrient concentration and host growth stage had a statistically significant effect on the phylogenetic composition of the attached bacteria. It was inferred that interactions between attached bacteria, as well as the inherent stochasticity mediating contact may also contribute to diatom-bacterial associations.