Genetic Relatedness of Heterocystous Cyanobacteria by Deoxyribonucleic Acid-Deoxyribonucleic Acid Reassociation

Abstract

I assessed the genetic relatedness of 45 strains of heterocyst-forming cyanobacteria assigned to eight genera by Rippka et al. and of 19 undescribed strains of the same group by in vitro reassociation of radioiodinated deoxyribonucleic acids. The members of the genera Nodularia, Cylindrospermum, Chlorogloeopsis, and Fischerella formed discrete clusters (intrageneric values of relative binding, more than 55%) and showed intergeneric relatedness of less than 40%, results consistent with the classification proposed by Rippka et al. The genus Nostoc was heterogeneous; four strains previously assigned to Anabaena appeared to belong to Nostoc. The genus Calothrix comprised four clusters with various degrees of internal homogeneity and two strains which showed low relatedness to any others. The general relatedness (i.e., relative binding) of heterocyst formers to various non-heterocystous cyanobacteria belonging to groups II and III (both unicellular and filamentous) was on the order of 10 to 20%.