Modification of hydrogen metabolism for improved ethanol production in thermophilic bacteria

Abstract

In this study; the changes in the production of ethanol and hydrogen resulting from the cellobiose fermentation were evaluated comparatively by performing deletion of the hfsA, hfsB, hfsC and hfsD genes (one-by-one) of the hfsABCD operon in wild-type Thermoanaerobacterium saccharolyticum and it has been found that the deletion of hfsA and/or hfsB gene resulted in about 1.8 fold increase in mutant T. saccharolyticum strain when compared to the wild-type. Enzyme activity assays have shown that alcohol dehydrogenase (AdhE) activity in mutant strains, where ethanol production is high, is about 2.0 fold higher than the wild type. Transcriptomic and proteomic studies have shown that this increase in ethanol production is related, in partly, to an increase in the expression of the adhE gene, suggesting the existence of a regulatory mechanism between hfsB and adhE. It has also been shown that the deletion of the hfsB gene causes an increase in ethanol production in other thermophilic anaerobes containing hfs-like hydrogenase. Among them, Thermoanaerobacterium xylanolyticum and Thermoanaerobacterium thermosaccharolyticum mutants have the highest ethanol yields reported in the literature to date. This suggests that hfB gene deletion can be used as a general genetic engineering method with the aim of increasing ethanol production in other microorganisms containing hfs-like hydrogenase.