Abstract: This invention provides a process for stabilizing a population of a mutant microorganism in a bioconversion system whereby growth of revertant cells is suppressed.The process involves limiting a nutrient which is essential for cell growth so that the cells selectively grow on a growth carbon source rather than on a non-growth carbon source which is present. The revertant cells being suppressed have a similar ability as the parent strain of the mutant microorganism to grow on the non-growth carbon source in the bioconversion system.The non-growth carbon source in the bioconversion system is metabolized to an extracellular accumulating quantity of a desired metabolite, e.g., toluene is converted to muconic acid.