The Effect of Proflavin, Ethidium Bromide and an Elevated Temperature on the Appearance of Nisin-negative Clones in Nisin-producing Strains of Streptococcus lactis
SUMMARY In some nisin-producing strains of Streptococcus lactis, clones which were permanently incapable of producing nisin (Nis−) appeared spontaneously with a frequency of 0·03 to 0·82 %. Treatment with proflavin (Pro), ethidium bromide (EB) or at a temperature of 40 °C increased the number of such clones. In one strain 78 % of cells became Nis− after treatment with Pro.
Treatment with nitrosoguanidine did not reverse the effect of Pro or EB. There was no evidence that Pro or EB selected spontaneously-occurring Nis− clones.
These observations suggest that the gene(s) responsible for nisin production in some S. lactis strains may be located on a plasmid, but further investigation is required to confirm this.
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The Effect of Proflavin, Ethidium Bromide and an Elevated Temperature on the Appearance of Nisin-negative Clones in Nisin-producing Strains of Streptococcus lactis