Identification of electron transfer enzymes in Thermoanaerobacterium saccharolyticum.

Thermoanaerobacterium saccharolyticum is a promising candidate for the production of biofuels from lignocellulosic sugars; however, the genes associated with electron transfer from ferredoxin are poorly characterized. In this work, we deleted several key electron transfer genes. We showed that the tsac_1705 gene is not necessary for high-yield ethanol production, but that a set of four other genes (nfnA, nfnB, hfsD, and hydA) are necessary. We showed that the nfnB gene can function as a monofunctional (i.e., non-bifurcating) FNOR enzyme in the absence of nfnA. The phenotypes of the hfsD, hydA, and hfsD hydA double-deletion strains are consistent with their function via hydrogen cycling.

Importance: The improved understanding of electron transfer pathways in T. saccharolyticum will enable future efforts to transfer the robust ethanol production pathway from this microbe to other organisms, with potential implications for industrial biofuel production.