Metabolomic analysis indicates a pivotal role of the hepatotoxin microcystin in high light adaptation of M icrocystis

Summary M icrocystis is a freshwater cyanobacterium frequently forming nuisance blooms in the summer months. The genus belongs to the predominant producers of the potent hepatotoxin microcystin. The success of M icrocystis and its remarkable resistance to high light conditions are not well understood. Here, we have compared the metabolic response of M icrocystis aeruginosa PCC 7806, its microcystin‐deficient Δ mcyB mutant ( M ut) and the cyanobacterial model organism S ynechocystis PCC 6803 to high light exposure of 250 μmol photons m −2 s −1 using GC/MS ‐based metabolomics. M icrocystis wild type and M ut show pronounced differences in their metabolic reprogramming upon high light. Seventeen per cent of the detected metabolites showed significant differences between the two genotypes after high light exposure. Whereas the microcystin‐producing wild type shows a faster accumulation of glycolate upon high light illumination, loss of microcystin leads to an accumulation of general stress markers such as trehalose and sucrose. The study further uncovers differences in the high light adaptation of the bloom‐forming cyanobacterium M icrocystis and the model cyanobacterium S ynechocystis . Most notably, M icrocystis invests more into carbon reserves such as glycogen after high light exposure. Our data shed new light on the lifestyle of bloom‐forming cyanobacteria, the role of the widespread toxin microcystin and the metabolic diversity of cyanobacteria.