# Physiological roles of pyruvate ferredoxin oxidoreductase and pyruvate formate-lyase in Thermoanaerobacterium saccharolyticum JW/SL-YS485

## TL;DR

This study identifies the roles of two enzymes in a thermophilic microbe that produces ethanol efficiently, showing how they contribute to energy and biosynthesis.

## Contribution

The study clarifies the physiological roles of PFOR and PFL in pyruvate metabolism in Thermoanaerobacterium saccharolyticum through gene deletion experiments.

## Key findings

- PFOR encoded by pforA is essential for pyruvate dissimilation.
- PFL encoded by pfl supports biosynthesis and compensates for PFOR loss.
- Deleting both pforA and pfl leads to reliance on acetate/formate and lactate production.

## Abstract

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.

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.

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.

The online version of this article (doi:10.1186/s13068-015-0304-1) contains supplementary material, which is available to authorized users.