Blue-green algal growth and sporulation in response to simulated surface bloom conditions

Physical and chemical factors were investigated for their effect on growth and differentiation of unialgal isolates and natural planktonic populations of blue-green algae from the Salopian meres under laboratory conditions. Most extensively investigated were two strains of Aphanizomenon flos-aquae (L.) Ralfs. Deficiencies of orthophosphate and nitrate, and of minor elements, were found to reduce growth but not to stimulate sporulation. N-glycyl-glycine inhibited both heterocyst differentiation and sporulation, and HEPES stimulated sporulation; but extracellular compounds contained in filtrates from sporulating cultures had no effect on morphology. Exposures to extremes of light intensity, and to u.v. light of 365 nm reduced and often stopped growth, but did not induce akinete formation in either of the algal isolates or in any of the populations collected from the lakes.