High efficiency hydrogen production from glucose/xylose by the ldh-deleted Thermoanaerobacterium strain

A strictly anaerobic, thermoacidophilic, H2-producing bacterium was isolated and designated as Thermoanaerobacterium aotearoense. The optimized cultivation conditions for H2 production are 55 °C, pH 6.5 and 10 g l−1 of glucose or xylose. A metabolic pathway analysis showed that lactate occupied most of the liquid metabolites and consumed a large amount of NADH. To increase the efficiency of hydrogen production, the gene encoding the l-lactate dehydrogenase was knocked out to redirect the NADH flow. Genetic manipulation resulted in the 2 and 2.5 folds increase of the H2 yield and production rate, respectively. The maximum H2 yields using the Δldh mutant were 2.71, 1.45 and 2.28 mol H2 mol−1 sugar under glucose, xylose and glucose/xylose mixture tests, respectively. The recombinant Δldh strain could ferment the mixture of glucose and xylose to produce H2 effectively, indicating that the performance of Thermoanaerobacterium in H2 production can be significantly improved by metabolic engineering technique.