Response of bacterioplankton communities and their phosphorus metabolic functions to algal extinction and growth in a eutrophic plateau lake

Phosphorus (P) control is critical for mitigating eutrophication, however, microbially driven P-cycling processes and their functional potential during algal succession remain elusive, especially in eutrophic plateau lakes. Here, we collected the overlying waters from algal decline, dormancy, recovery and outbreak periods in a large plateau lake of Southwest China, and examined the dynamic response of bacterioplankton communities and their P-functional genes to algal extinction and growth. We found that bacterioplankton composition showed significant differences among four distinct periods, and their diversity was highest in recovery period and lowest in outbreak period. During algal growth, the dominant phylum of bacterioplankton gradually switched from Proteobacteria to Actinobacteria. Rhodococcus, belonging to Actinobacteria, could effectively solubilize the inorganic P (Pi) from calcium phosphate (Ca-P) to intensify lake eutrophication. Notably, bacterioplankton communities with lower diversity exhibited higher stability. Bacterioplankton network was tightly connected in outbreak period with lower substructure, stronger interaction and higher complexity compared with other periods. Moreover, we detected high-abundance genes associated with phosphoester hydrolysis (e.g., ugpQ), purine metabolism (e.g., ppx), oxidative phosphorylation (e.g., ppk and ppa) and P transport (e.g., pstS). Bacterioplankton secreted gluconic acid by activating gcd to solubilize Ca-P in outbreak period, and activated ppx to regulate pppGpp in response to environmental stresses like dissolved oxygen. Note that organic phosphate mineralization was primarily regulated by phnK in dormancy and recovery periods, and by phoD, phoX, bpp and cphy in outbreak period. By encoding ppk, bacterioplankton polymerized the excess Pi into polyphosphates for continuing P cycle. Collectively, our study provides a valuable microbial perspective to decipher the mechanism of P metabolism response to algal succession in plateau lakes, which can advance the understanding and management of eutrophication.