Physiological regulation of Cylindrospermopsis raciborskii (Nostocales, Cyanobacteria) in response to inorganic phosphorus limitation

Physiological responses to varying dissolved inorganic phosphorus (DIP) levels were examined to explore the acclimation mechanisms of Cylindrospermopsis raciborskii, a nontoxic diazotrophic cyanobacterium. The results showed that the growth rate of C. raciborskii was markedly reduced under phosphorus (P)-deficient conditions. Photosynthetic activity in terms of Fv/Fm (maximum quantum yield), ETRmax (maximum electron transport rate), α (photosynthetic efficiency) and Ik (saturation irradiance) was also found to be significantly lower after a 12-day incubation with a Pi concentration of less than 0.05 mg L−1. When supplied with phosphorus concentrations of more than 0.50 mg L−1, C. raciborskii showed increased growth rates and reached a relatively stable value, about 0.26 d−1. Additionally, the content of malodialdehyde (MDA), a lipid peroxidation product reflecting the destruction of lipid membrane by environmental stresses, in Cylindrospermopsis cultured with a low P concentration was 10.81–12.13 times higher than that with a high P concentration. The relative activities of catalase (CAT) and extracellular phosphatase (APA) were found to increase significantly to reduce the stress of P limitation and compensate for P deficiency. These data indicate that C. raciborskii is able to regulate its physiological metabolism in order to acclimate to low ambient DIP environments.

► Growth and photosynthesis of C. raciborskii are markedly inhibited under P-deficient conditions. ► The malodialdehyde (MDA) content increases at low P concentrations. ► The activities of CAT and APA show significant increases at low P concentrations. ► C. raciborskii could regulate its physiological metabolism to acclimatize to Pi conditions.