Nature of UV resistance in the cyanobacterium Nostoc linckia

Abstract

After several exposures of Nostoc linckia to ultraviolet radiation an UV -resistant strain was isolated. When this strain was subcultured for 5 to 6 generations in medium supplemented with 1 µg ml^-1 of acridine orange and then exposed to UV irradiation, the resistant character was lost and it behaved like a wild strain. Agarose gel electrophoretic analysis of crude lysate DNA revealed the presence of three classes of covalently closed circular DNA bands in the UV -resistant strain, but their absence in the strain which had been cultured in acridine orange. This finding suggests the involvement of extra chromosomal genetic elements in UV resistance in N. linckia.