Physiological role of pyruvate ferredoxin oxidoreductase and pyruvate formate lyase in Thermoanaerobacter saccharolyticum

The conversion of pyruvate to acetyl-CoA is a key pathway in ethanol formation. Genes and enzymes responsible for conversion of pyruvate to acetyl-CoA in Thermoanaerobacter saccharolyticum were identified using gene deletion.  It was found that pyruvate formate oxidoreductase (PFOR) is encoded by pfor_0046 and plays a key role in pyruvate dissimilation.  We further demonstrated that pyruvate formate lyase is encoded by pfl_0628.  Although the pfl_0628 is normally expressed at low levels, it is crucial for biosynthesis in T. saccharolyticum.  In pfor_0046 deletion strains, pfl expression increases, and is able to partially compensate the loss of PFOR activity.  Deletion of both pfor_0046 and pfl_0628 results in a strain that requires acetate for growth and produces lactate as the primary fermentation product, achieving 88% of theoretical lactate yield. It is concluded that these two enzymes are the main routes of acetyl-CoA formation from pyruvate in T. saccharolyticum.