title: Physiological roles of pyruvate ferredoxin oxidoreductase and pyruvate formate-lyase in Thermoanaerobacterium saccharolyticum JW/SL-YS485.
abstract: BACKGROUND
  Thermoanaerobacter saccharolyticum is a thermophilic microorganism that has been engineered to produce ethanol at high titer (30-70 g/L) and greater than 90 % theoretical yield. However, few genes involved in pyruvate to ethanol production pathway have been unambiguously identified. In T. saccharolyticum, the products of six putative pfor gene clusters and one pfl gene may be responsible for the conversion of pyruvate to acetyl-CoA. To gain insights into the physiological roles of PFOR and PFL, we studied the effect of deletions of several genes thought to encode these activities.
  
  
  RESULTS
  It was found that pyruvate ferredoxin oxidoreductase enzyme (PFOR) is encoded by the pforA gene and plays a key role in pyruvate dissimilation. We further demonstrated that pyruvate formate-lyase activity (PFL) is encoded by the pfl gene. Although the pfl gene is normally expressed at low levels, it is crucial for biosynthesis in T. saccharolyticum. In pforA deletion strains, pfl expression increased and was able to partially compensate for the loss of PFOR activity. Deletion of both pforA and pfl resulted in a strain that required acetate and formate for growth and produced lactate as the primary fermentation product, achieving 88 % theoretical lactate yield.
  
  
  CONCLUSIONS
  PFOR encoded by Tsac_0046 and PFL encoded by Tsac_0628 are only two routes for converting pyruvate to acetyl-CoA in T. saccharolyticum. The physiological role of PFOR is pyruvate dissimilation, whereas that of PFL is supplying C1 units for biosynthesis.
authors.affiliation: Thayer School of Engineering, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Jilai
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Thayer School of Engineering, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Olson
authors.affiliation: Thayer School of Engineering, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Lanahan
authors.affiliation: Thayer School of Engineering, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Tian
authors.affiliation: Thayer School of Engineering, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Sean Jean-Loup
authors.initials: SJ
authors.lastname: Murphy
authors.affiliation: Department of Biological Sciences at Dartmouth College, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lo
authors.affiliation: Thayer School of Engineering, Hanover, NH 03755 USA ; Department of Biological Sciences at Dartmouth College, Hanover, NH 03755 USA ; BioEnergy Science Center, Oak Ridge, TN 37830 USA.
authors.forename: Lee R
authors.initials: LR
authors.lastname: Lynd
keywords: C1 metabolism; Pyruvate ferredoxin oxidoreductase; Pyruvate formate-lyase; Pyruvate metabolism; Thermoanaerobacter saccharolyticum