No abstract

Pseudomonas diminuta and P. vesicularis, two obligate aerobes isolated from laboratory algal cultures, stimulated the growth of the green microalgae Scenedesmus bicellularis and Chlorella sp., without releasing any growth promoting substance. An intimate contact between both microorganisms was necessary for significant algal growth enhancement. The possibility of algal growth stimulation by bacterial attenuation of photosynthetic oxygen tension was indirectly examined by simulating the effect of bacteria through a physical removal of oxygen (air suction). Vacuum‐treated cultures showed an increase in growth rate and photosynthetic activity as compared to the control, a result which cannot be explained by differences in CO2/HCO3− pump activity. In the presence of P. diminuta, the photosynthetic activity of S. bicellularis was more strongly stimulated under a limited concentration of inorganic carbon. It is suggested that, apart from a CO2 supply, aerobic bacteria can promote algal growth by reducing the photosynthetic oxygen tension within the microenvironment of the algal cells, thereby creating more favorable conditions for optimal photosynthetic algal growth.