Interactive mechanism of elevated pCO₂ and nutrient on 2-methylisoborneol production in cyanobacteria

Cyanobacterial blooms, exacerbated by climate change and eutrophication, increasingly compromise water quality by producing taste and odor (T&O) compounds including 2-methylisoborneol (MIB). Cyanobacteria synthesize MIB by redirecting carbon metabolism intermediates into the methylerythritol phosphate pathway. This process appears to be influenced by rising atmospheric CO₂ partial pressure (pCO₂). This study examines how elevated pCO₂ affects MIB production in Synechococcus sp. FACHB-1061 under varying nutrient conditions. The results indicate that elevated pCO₂ boosts cyanobacterial biomass and total MIB yield, particularly in nutrient-rich environments, by reducing limitations in bioavailable inorganic carbon. In contrast, in nutrient-limited conditions, both total MIB concentration and per-cell production significantly increased with higher pCO₂. Elevated pCO₂ altered the activities of nitrate reductase and carbonic anhydrase, reducing impaired nitrogen assimilation and enhanced carbon fixation. The increase and compositional changes in extracellular polymeric substances suggested carbon overflow and a decline in cellular quality under insufficient nutrients. Additionally, markers of oxidative stress, such as increased superoxide dismutase activity and higher malondialdehyde levels, suggested that oxidative stress might stimulate secondary metabolite production. Metabolomic analysis revealed that critical intermediates of the Calvin cycle and glycolysis, such as glyceraldehyde-3-phosphate and acetyl-CoA, were upregulated with elevated pCO₂ in nutrient-limited status, leading to increase of key precursors for MIB. These results highlight the complex interplay between nutrient and rising pCO₂ in regulating cyanobacterial MIB biosynthesis. The findings suggest that conventional nutrient control strategies for mitigating cyanobacterial blooms and associated T&O issues may need reassessment under future climate scenarios.