Hydrogen Production, Adaptive Evolution and Transcriptomeanalysis of Metabolic Engineered Thermoanaerobacterium sp. strain

Hydrogen is regarded as an attractive future energy carrier for its high energy content and zero CO2 emission. The strictly anaerobic, gram-positive bacterium, Thermoanaerobacterium aotearoense SCUT27 is a promising strain for hydrogen production because it has the capability of utilizing glucose and xylose almost simultaneously. However, a metabolic pathway analysis pointed that lactate occupied most of the liquid metabolites and consumed a large amount of NADH. In order to promote hydrogen yield, the lactate metabolic pathway was blocked to redirect the carbon flux and total cellular NADH distribution. After gene modification, an increase of 2
and 2.5 folds for H2 yield and production rate were achieved, accompanied by 2.4 folds for ethanol yield. The maximum H2 yields using the Î?ldh mutant were 2.71, 1.45 and 2.28 mol H2 mol-1 sugar under glucose, xylose and glucose/xylose mixture tests, respectively. Moreover, we tried to use agro-industrial by-products as substrate to yield hydrogen. After an optimization of acid hydrolysis by Response Surface Methodology (RSM), sugarcane bagasse was utilized by T. aotearoense SCUT27Î?ldh, to result a best hydrogen yield of 1.86 mol H2/mol total sugar and a hydrogen production rate (HPR) of 0.52 L/L · h in a 5-L fermentor.

More work was performed on T. aotearoense SCUT27Î?ldh. In order to reduce the lag time when the strain grew in the medium containing high concentration sugar (>80 g/L) and enhance hydrogen productivity, it was adaptively evolved to yield the mutant strain, SCUT27Î?ldh G3#4. Compared with SCUT27Î?ldh, G3#4 decreased the lag time from 82 h to 12 h (from inoculation to OD600 = 0.5) in the medium with 120 g/L carbon source. In a 5-L fermentor containing 2 L medium, the maximum hydrogen production and HPR were 3.09 L and 0.28 L/L·h. Transcriptome data showed that the UDP-Glucose was accumulated in SCUT27Î?ldh G3#4, which is the
precursor of trehalose, and the latter one acted as a compatible solute to help cell survive from high permeability environment.

Keywords:
Thermoanaerobacterium aotearoense / Metabolic engineering / Hydrogen production / Adaptive evolution

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