On the nature of streptomycin-resistance in Chlorella

Abstract

As it was shown in previous publication, the streptomycin resistant to 500 units/ml mutations (sr-500) arise in clones of Chlorella only on solid media with streptomycin and therefore we regard them as non-preadaptive. Now we try to investigate the nature of sr-500 mutations by growing colonies before fluctuation test on a media with low streptomycin concentration and by testing bigger colonies. Cultivation of sensitive cells (ss) of Chlorella vulgaris (strain B) on low selecting dose of streptomycin (20 unitslml) led to the discovery of preadaptive clones, resistant to 500 unitslml. The fluctuation analysis of big clones of sensitive cells can reveal the infrequent cases of preadaptation to streptomycin. Heterogeneity of clones of resistant mutants is a indirect indication on a multistage process of adaptation to streptomycin. The adaptation of Chlorella cells to streptomycin could be considered as the results of selection and mutations in presence of the inhibitor.