EVIDENCE FOR INTERGENERIC TRANSFORMATION IN FILAMENTOUS, DIAZOTROPHIC CYANOBACTERIA

A clonal population of a mutant Nostoc muscorum, with the ability to assimilate azide as a fixed nitrogen source, was used as a source of donor DNA for transforming Anabaena doliolum from an azide-sensitive to an azide-assimilating phenotype. The donor DNA. transformed A. doliolum efficiently and the transformation process was sensitive to DNAase, resistant to RNAase A, dependent on photosynthetic light and required a specific contact period between donor DNA and recipient cells. The gene(s) responsible for azide assimilation appear to be located on chromosomal DNA and not on plasmid DNA. The transformants of A. doliolum resemble the azide assimilating mutant strain of N. muscorum in respect of (1) azide repression of heterocyst and nitrogenase formation, (2) azide-dependent increase in phycocyanin to chlorophyll ratio. These results suggest that the chromosomal DNA of mutant N. muscorum, and not its plasmid DNA, is the carrier of genetic information for its azide assimilatory phenotype and that this can be transferred efficiently to A. doliolum.