The extracellular products ofAnabaena cylindricaLemm. III. Excretion and uptake of fixed nitrogen

Pseudomonas aeruginosa Chemotaxis Associated with Blooms of N 2 -Fixing Blue-Green Algae (Cyanobacteria)

Pseudomonas aeruginosa (Schroeter) Migula, a numerically significant bacterium found during N 2 -fixing blooms of the blue-green algae (cyanobacteria) Anabaena sp. in the Chowan River, North Carolina, was chemotactically attracted to amino acids when tested in a radioassay. The bacterium was labeled with 32 P i , and the disintegrations per minute determined by liquid scintillation counting were proportional to the number of cells accumulating in microcapillaries containing amino acids. Positive chemotaxis was observed toward all of the amino acids tested, although the degrees of response varied. Since many nitrogen-fixing blue-green algae secrete nitrogenous compounds, this attraction may be instrumental in establishing a symbiotic relationship between this bacterium and blue-green algae in freshwater.

Role of heterotrophic bacteria in promoting N2 fixation byAnabaena in aquatic habitats

Anabaena species are commonly colonized by bacteria, especially during N2-fixing blooms. Generally these associations do not represent bacterial attack on algal hosts. Instead, the algal N2-fixing capabilities are increased in the presence of the bacteria. Possible mechanisms promoting the mutual growth of algae and attached bacteria were investigated by observing specific sites of bacterial attachment, by noting reduced microzones created by the bacteria, and by locating sites of bacterial uptake of organics representative of algal excretion products.Attached bacteria show preference for typical algal excretion products and their growth is enhanced by such products. In return, enhancement of algal nitrogenase activity occurs when bacteria create O2-consuming microzones around the nitrogenase-bearing heterocysts.