Roles of Attached Bacteria on the Growth and Metabolism of Microcystis aeruginosa with Limited Soluble Phosphorus

The limited endogenous soluble phosphorus (P) in lake sediment is a potential and non-negligible P pool for the growth of Microcystis species and the bacteria attached to them. The attached bacteria are considered as P utilization supporters that contribute to Microcystis blooms; however, their effects on Microcystis growth and metabolism during the utilization of limited soluble P are poorly understood. Here, a series of cocultivations of Microcystis aeruginosa and a Microcystis growth-promoting bacterium, Brucella sp., were conducted using two P sources with limited solubility (tricalcium phosphate and calcium phytate). The results indicated that Brucella sp. secreted auxins to directly promote the growth of M. aeruginosa, and the secreted organic acids and alkaline phosphatase accelerated the overall P solubilization and transformation. In addition, the coexistence of M. aeruginosa with Brucella sp., which resulted in competition for P, stimulated M. aeruginosa to synthesize more photosynthetic pigments and alkaline phosphatase. Therefore, the results revealed that the attached bacteria improved the properties of M. aeruginosa and the phycosphere (e.g., the availability of P sources), providing comprehensive insights into their contribution to endogenous P utilization by Microcystis and the further occurrence of cyanobacterial blooms.