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

A method for producing ethanol comprising contacting a recombinant bacterium with a fermentable substrate in an anaerobic environment without antibiotics in an amount and under conditions effective to produce ethanol from said substrate,

• wherein said recombinant bacterium comprises a mutant bacterium which has been transformed with heterologous DNA to produce the recombinant bacterium,
• wherein said mutant bacterium comprises mutations that decrease activities required for fermentative reduction of pyruvate to the extent that the mutant bacterium is rendered incapable of anaerobic fermentative growth,
• wherein said heterologous DNA encodes alcohol dehydrogenase and pyruvate decarboxylase, and
• wherein said recombinant bacterium is capable of anaerobic growth and expresses said heterologous DNA at a sufficient level for the recombinant bacterium to produce ethanol as a primary fermentation product.