Metabolomic Analysis of Both Microcystin-Producing and Microcystin-Free Microcystis aeruginosa Strains in Response to Exogenous Microcystin Exposure

Microcystis aeruginosa (M. aeruginosa), a key species in cyanobacterial blooms, is notably concerning due to its production of harmful microcystins (MCs). In this study, the differences in the ability of MC-producing and MC-free strains of M. aeruginosa to respond to the exogenous MCs (MC-LR) were compared. The results showed that at higher concentrations, MC-LR affected cell morphology, cell growth, photosynthetic efficiency, and induced oxidative stress in M. aeruginosa. Under high MC-LR concentration exposure, MC-producing strains showed a 14.7% reduction in cell density, accompanied by a 32% elevation in Vj and a 63.1% decline in FV/FM. MC-free strains showed cell density decreasing by 22.5%, Vj increasing 2-fold, and FV/FM dropping by 69.5%. The inhibitory effect of MC-LR at higher concentrations was found to be stronger in MC-free compared to MC-producing strains. In addition, MC-LR reduced the efficiency of photosystem II by blocking electron transfer from QA to QB; for MC-free strains, MC-LR may have acted as a signaling molecule affecting the targeting of QB on the D1 protein, thus leading to QB detachment from the protein complex. Metabolomics analysis showed that MC-LR affects arginine synthesis in M. aeruginosa and thus the synthesis and release of MCs.