Microbial conversion of lonophorous antibiotic nigericin by the ciliate Tetrahymena pyriformis.

The ionophorous antibiotic nigericin is toxic towards the ciliate Tetrahymena pyriformis GL. At the high concentration of 30 mg/l (sublethal dose), it is bioconverted into several products. The yield of one of these (N1) is appreciably improved with pretreated cells, higher concentrations of nigericin (50 or 100 mg/1), and the presence of a larger ciliate biomass. A structural study of N1 by FAB mass spectrometry combined with tandem mass spectrometry and nuclear magnetic resonance shows it to be an epimer, epinigericin, about half as toxic as nigericin. Bioconversion of nigericin by T. pyriformis may be regarded as a detoxication process.