Specific Adhesion of Bacteria to Heterocysts of Anabaena spp. and Its Ecological Significance.

Two bacterial isolates, Pseudomonas sp. SL10 and Zoogloea sp. SL20, attach to heterocysts of Anabaena spp. with a high degree of selectivity, and this attachment can be expressed quantitatively in terms of adsorption isotherms. Adhesion of Pseudomonas sp. SL10 was restricted to a monolayer and exhibited a type I (Langmuir) isotherm, whereas adhesion of Zoogloea sp. SL20 involved multilayer attachment and exhibited a type II isotherm. The degree of adhesion by the bacteria to heterocysts of different Anabaena species may reflect the distribution and abundance of binding sites on the surface of different heterocysts. Both Pseudomonas sp. SL10 and Zoogloea sp SL20 promoted higher rates of acetylene reduction by Anabaena spp. under oxygenated culture conditions when compared with a cyanobacterial control. At ambient oxygen levels, however, only Zoogloea sp. SL20 stimulated acetylene reduction by Anabaena spp.