The effect of proflavine on different strains of the blue-green alga Anacystis nidulans

Abstract

The growth of the blue-green alga Anacystis nidulans was inhibited by relatively low concentrations of proflavine. The duration of the lag phase increased linearly with increasing proflavine concentrations. The alga neither acquired increased tolerance to the drug during the course of six subcultures in proflavine-supplemented media nor was there any shortening of lag-phase or increase in final population density following repeated subculture in proflavine medium. The strain obtained after six subcultures in proflavine was found to have become more sensitive to streptomycin than the untreated stock strain. A comparison of sensitivity to proflavine of two streptomycin-resistant strains and of untreated stock strain of the alga revealed that the streptomycin-resistant strains were less sensitive to proflavine than the untreated strain. The resistance of a strain resistant to 200 µg streptomycin/ml was lost after it had been cultured once in streptomycin-free basal medium that had been supplemented with 1 µg proflavine µml. The results obtained provide some indirect evidence for the existence of episome in A. nidulans.