Genetic modifications and introduction of heterologous pdc genes in Enterococcus faecalis for its use in production of bioethanol

Genetically-modified Enterococcus faecalis has a potential of survival and can be used in ethanolic fermentations. Fermentation profiles of E. faecalis JH2-2 were assessed using glucose and lactose as carbon sources. Deletion of lactate dehydrogenase ( ldh ) genes increased the ethanol production from 0.25 to 0.82 g/l, which was further increased to 0.96 g/l by the insertion of a pyruvate decarboxylase ( pdc ) gene (from Sarcina ventriculi or Clostridium acetobutylicum ) in place ldh1 . When grown on lactose, the pdcSv and pdcCa showed 13.6 and 17.6 U mg −1 of pdc specific activity, respectively. Highest activity (47 U mg −1 ) and ethanol concentration (2.3 g/l) were obtained with pdcCa using an expression plasmid. Formate and acetate were also produced in high quantities. Transcriptional analysis showed that aldehyde alcohol dehydrogenase gene was upregulated up to 16-fold. Further optimizations are required for higher ethanol production.