[Growth inhibition by antibiotics and the production of resistance to them in a population of Nostoc linckia]

Abstract

Increasing concentrations of penicillin and streptomycin inhibited the growth of the blue-green alga Nostoc linckia. Although the alga could build up resistance to higher concentrations of penicillin (1000 mcg/ml), it was very sensitive to streptomycin beyond a concentration of 0.02 mcg/ml. Two stable mutants, one resistant to 1000 mcg penicillin/ml and another to 0.02 mcg streptomycin/ml were isolated, of which the latter had lost its nitrogen fixing capacity. Drug resistance seems to be due to nuclear or gene mutation.