Mutagenic And Plasmid-eliminating Action Of Acridine Orange In The Cyanobacterium Nostoc

Abstract

Acridine orange was poorly mutagenic but strongly inactivating in Nostoc. The wild type organism is heterocystous and resistant to polymixin B. From this, a non-heterocystous, polymixin B resistant (Het -Pmbr) strain was produced by mutagenesis, and a non-heterocystous, polymixin B-sensitive (Het -Pmbs) strain was produced by six successive subcultures in a medium containing acridine orange. Agarose gel electrophoretic analysis of crude lysate DNA revealed the presence of three classes of covalently closed circular (CCC) DNA bands in the wild type but their absence in the Het -Pmbs strain. This suggests the probable involvement of extrachromosomal genetic elements in heterocyst differentiation and polymixin B tolerance in this organism. A tentative working model is proposed to infer the possible genotypic basis of the observed phenotypes.