Selective isolation of blue-green algae from water and soil.

For the isolation of blue-green algae from soil and fresh water, temperature is a selective factor of major importance. In a nutritionally non-selective mineral medium, which at 25" supported growth of blue-green algae and of many eucaryotic algae, the development of eucaryotic algae was almost completely suppressed by incubation at 35". Both the number and variety of blue-green algae recoverable at 35" were greater than those recoverable from parallel cultures incubated at 25". When a combined-nitrogen source was omitted from the enrichment medium, only blue-green algae developed at both 25" and 35" ; the microflora consisted exclusively of heterocyst-forming filamentous types, other groups of blue-green algae being eliminated.