UV-C suppression on hazardous metabolites in Microcystis aeruginosa: Unsynchronized production of microcystins and odorous compounds at population and single-cell level

The effectiveness of UV-C towards the toxin and odor of M. aeruginosa at population and single cell levels were investigated in three ways. In the absence of UV-C, MC-LR and β-cyclocitral production show similar pattern of incremental rate with growth rate on population level shown as intracellular concentrations of MC-LR (C_MC) and β-cyclocitral (C_BCC), but the cellular quota of MC-LR (Q_MC) and β-cyclocitral (Q_BCC) at single-cell level reached the maximum values, 37.5 ± 1.2 fg cell⁻¹ and 4.3 ± 0.1 fg cell⁻¹, just after the early exponential phase. Second, upon UV-C irradiation, the C_MC consistently decreased by 10–41% with increase of UV-C dosage (50–200 mJ cm^-2) while C_BCC increased by 2–14%. Third, during the 14 days’ post-UV incubation, UV-C at 75–200 mJ cm^-2 induced remarkable suppressing effects on both C_MC and C_BCC for 3–14 days. The suppressing effects on Q_MC and Q_BCC were induced by UV-C at 100 mJ cm^-2 and above, with shorter suppressing periods by 1–4 days and lower decremental rates by 21%–30% than that of C_MC and C_BCC, indicating interruptions on biosynthesis processes partially contribute to suppression effects of C_MC and C_BCC. The suppression effect on either C_BCC or Q_BCC, with higher decrement rates while lower recovery rates, was more severe than C_MC and Q_MC.