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