Growth responses of pure cultures of Microcystis aeruginosa to carbon dioxide, phosphate, and nitrate are studied to identify the limiting nutrient. Experiments were conducted on growth of the obligate aerobic bacterium, Pseudomonas aeruginosa for use as a model bacterium in investigation of symbiotic two-species bacterial/algal cultures which may be significant in the eutrophication process. In addition, evidence was found that bacteria removes algal toxic agents which may explain why algae blooms sometimes appear so suddenly and unexpectedly. One bacterial and one algal specie were grown in the same vessel under controlled conditions after the algae were purified of contaminating bacteria. Its responses to glucose, pH, light intensity, and aeration, and agitation rate were determined. During the purification of the algae other interactions occurred in addition to the transfer of oxygen from algae to bacteria and the reverse transfer of carbon dioxide from bacteria to algae: two that were very obvious were the transfer of organic excretions to the bacteria and the breakdown of agents toxic to the algae.