Photosynthetic advantage promotes Microcystis competitiveness against Scenedesmus: Synchronized dynamics and structure shifts in symbiotic microbiomes

Abstract

Microcystis threaten aquatic ecosystems because of its low nutritional value and cyanotoxin production. While its stress-induced photosynthetic enhancement under nutrient limitation is recognized, the role of interspecific competition in driving photo-physiological adaptation remains unclear. Field observations reveal synchronized restructuring of Microcystis-associated symbiotic microbiomes with algal dominance shifts, while their dynamics in laboratory competition systems remain poorly understood. We investigated Microcystis aeruginosa–Scenedesmus obliquus interactions under controlled competition, revealing: (1) S. obliquus presence triggered M. aeruginosa photosynthetic upregulation; (2) the specific growth rates and carrying capacities of both algae were mutually inhibited, with M. aeruginosa exerting a stronger inhibitory effect on S. obliquus than vice versa; (3) the structure and composition of the symbiotic microbial community changed in tandem with the increasing dominance of M. aeruginosa; (4) the relative abundance of bacteria associated with M. aeruginosa, including Rhodobacter, Porphyrobacter, and Methylophilus, gradually increased in parallel with the dominance of M. aeruginosa. These results indicate that enhanced photosynthesis facilitates the competitive advantage of M. aeruginosa over S. obliquus and emphasize the synchronized dynamics of the symbiotic microbial community, resembling patterns observed in natural waters. Our findings provide insights into cyanobacterial succession, informing bloom prediction and microbial management strategies.