SUMMARY: An examination was made of soluble extracellular materials produced by cylindrica and some other species of blue-green algae, to exasmine whether they have any functional importance. Organisms of all the 15 species (representing 10 genera) examined produced extracellular pigment; with at least 10 of these species part of this pigment was not dif-fusible on dialysis, though the actual amount varied from 14 to 50%. The dialysis residue fractions of the extracellular products of A. and 4 other species had similar amino acid compositions, rather different from those of extracellular polypeptides produced by other micro-organisms. The algal polypeptides had large proportions of serine and glycine, but no basic amino acids. The dialysis residue fraction of A. extracellular product had no effect on spore formation and did not cause an increase in uptake of phosphate. A biological effect of this fraction was the decrease in the toxic effect of polymyxin B against A. . For the latter organism there was a linear relationship between concentra-tion of polymyxin B and amount of algal dialysis residue fraction which just permitted the alga to survive. This effect of extracellular products on polymyxin B toxicity might operate in nature since often occurs in association with blue-green algae.


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