Stabilization of PET operon plasmids and ethanol production in bacterial strains lacking lactate dehydrogenase and pyruvate formate lyase activities

Recombinant bacteria are disclosed which are transformed with heterologous DNA coding for alcohol dehydrogenase (adh) and pyruvate decarboxylase (pdc), and which are effective for use in the production of ethanol, but which do not require the presence of antibiotics in the culture medium to maintain genetic stability and high ethanol productivity. These recombinant bacteria are produced using mutant host strains which are substantially deficient in the ability to fermentatively reduce pyruvate. When grown in an anaerobic environment, the recombinant pyruvate mutants transformed with the adh and pdc genes are genetically stable, maintaining the inserted genes and ethanol productivity even in the absence of antibiotics.