Production of megacins C and Cx: presumptive evidence extrachromosomal control.

Exposure of growing cultures of Bacillus megaterium C4A(-) to ethidium bromide or an elevated growth temperature was found to eliminate megacin C production. Ethidium bromide resulted in a cure rate of up to 13%. Growth at 43 degrees C gave a cure rate of up to 99%. Megacin C production was lost spontaneously at a rate of 4% or less. There was a greater rate of spontaneous loss of megacin Cx production by B. megaterium 337, up to 14%. Growth at 43 degrees C resulted in a cure rate of up to 24% in this organism. Reversion to the Meg(+) state by cured clones has never been demonstrated. These observations support the hypothesis that production of megacins C and Cx is plasmid mediated. Meg(-) clones adsorbed more megacin than either parent strain and were more susceptible to megacin action.