The coexistence of bacteria and algae has been widely documented in many different ecosystems. Prymnesium parvum or golden alga are known to obtain key nutrients from planktonic and symbiotic bacteria. Such nutrient exchanges play a critical role in the cycling of phosphorus, nitrogen and sulfur, impacting algal growth. However, the response of symbiotic bacterial communities to varied abiotic conditions that influence algal growth has not been addressed. In our study, the response of the microbiome of P. parvum to varying nutrient conditions was analyzed to understand if the algal microbiome changes in response to larger habitat conditions of the algae. Prymnesium parvum was grown at 22 ± 1°C on a 12 h:12 h light: dark cycle for six weeks. The samples were grown in F/2 media with different nitrate and phosphate concentrations. A set of P. parvum samples was also incubated in complete darkness for six weeks by covering the entire media flask with aluminum foil. DNA was extracted from P. parvum samples using the Mo Bio POWER WATER DNA Isolation Kit and sequenced using the Illumina Mi Seq platform to elucidate the bacterial microbiome that developed under various conditions.
Results/Conclusions
At the end of the growth cycle (6 weeks), four bacterial phyla were identified in all samples, of which Bacteroidetes and Proteobacteria had the highest relative abundance. The most dramatic change in relative abundance of bacteria was observed when the concentration of NaH2PO4 was changed in the growth media. As the NaH2PO4 concentration in the media was increased from 0 µM to 36 µM (the recommended amount for growing P. parvum in culture) while maintaining the NaNO3 concentration constant at recommended 880 μM, the relative abundance of Proteobacteria decreased from 72% to 43%. In comparison to the relative abundance of Proteobacteria grown in 12 h:12 h light: dark cycle (43%), the relative abundance of this phylum rose to 95% when grown in complete darkness. At the species level, Roseobacter (which belongs to the class Alphaproteobacteria) constituted 49% of all identified taxa when grown in complete darkness, as compared to only 23% when grown 12 h:12 h light: dark cycle. This may be crucial as the Roseobacter clade is often associated with marine algal blooms and plays a crucial role in biogeochemical cycling of carbon and sulfur. Understanding the abiotic response of the golden algae microbiome may provide a biological control mechanism to reduce harmful algal blooms.