Growth, extracellular alkaline phosphatase activity, and kinetic characteristic responses of the bloom-forming toxic cyanobacterium, Microcystis aeruginosa, to atmospheric particulate matter (PM2.5, PM2.5–10, and PM>10)

Atmospheric particulate matter (APM), commonly seen and widely excited in environment, appears great enough to influence the biochemical processes in aquatic microorganisms and phytoplankton. Understanding the response of cyanobacteria to various factors is fundamental for eutrophication control. To clarify the response of cyanobacteria to APM, the effects of PM₂.₅, PM₂.₅–₁₀, and PM>₁₀ on Microcystis aeruginosa were researched. Variabilities in cell density, chlorophyll a, soluble protein, malondialdehyde, extracellular activity, and kinetic parameters of alkaline phosphatase were evaluated by lab-cultured experiments. Results showed that the PM₂.₅ had a slight stimulation impact on the growth and enhanced both of the 48- and 72-h extracellular alkaline phosphatase activity (APA), the affinity of alkaline phosphatase for substrate, and the 72-h maximum enzymatic reaction velocity (Vₘₐₓ). Moreover, the stimulations in extracellular APA and Vₘₐₓ enhanced with the increasing exposure concentrations. We also found there were no obvious distinctions on the effects of growth and alkaline phosphatase in M. aeruginosa between PM₂.₅–₁₀ and PM>₁₀ exposure groups. Obviously, inhibitory effects on growth existed in 4.0 and 8.0 mg/L PM₂.₅–₁₀ and 8.0 mg/L PM>₁₀ at 120 h. Furthermore, PM₂.₅–₁₀ and PM>₁₀ exerted inhibitory effects on the extracellular APA during the 72-h exposure. Simultaneously, the Vₘₐₓ was notably inhibited and the affinity of alkaline phosphatase for substrate was more inseparable compared with control in PM₂.₅–₁₀ and PM>₁₀ treatments. Nevertheless, the inhibitors in extracellular APA and kinetic parameters were unrelated to PM₂.₅–₁₀ and PM>₁₀ exposure concentrations. Two-way ANOVA results revealed that there were significant interactions between exposure concentration and diameter of APM on the 120-h cell density, soluble protein content, APA, and 72 h APA of M. aeruginosa. These results in our study would be meaningful to further researches on relationships between APM deposition and cyanobacterial bloom.