The isolation and growth of axenic cultures of planktonic blue—green algae

A procedure for isolating axenic cultures of planktonic blue-green algae is described that relies on a filtration procedure to produce a high filament: bacteria ratio and a subsequent serial dilution to isolate axenic algal filaments. Six axenic cultures have been prepared and their growth kinetics compared with the corresponding bactericized cultures. In continuous light, two axenic cultures exhibited sub-optimal growth whereas the remainder grew essentially as well as their bactericized counterparts. By contrast, under a light: dark regime two axenic cultures exhibited significantly better growth, and another, significantly poorer growth than the bactericized cultures. The causal factors of the poor growth of Oscillatoria agardhii Gom. were investigated, and it was concluded that the role of bacteria may be an active metabolic one, possibly involving the recycling of algal extracellular products.