Improvement of hydrogen yield by ethanol producing Escherichia coli recombinants in acidic condition

Abstract

Background: An effective single culture that have high glycerol consumption and hydrogen and ethanol co-production yield is still in demand. Local isolate glycerol consumer Escherichia coli SS1was found to produce lower hydrogen under optimized ethanol production condition. Molecular approach was proposed to improve hydrogen yield of E. coli SS1 while maintaining the ethanol yield, particularly at acidic condition. Hence, the effect of additional copy of native hydrogenase gene hycE and recombinant clostridial hydrogenase gene hydA on hydrogen production by E. coli SS1 at low pH was investigated.

Results: The E. coli recombinant with additional copy of hycE and clostridial hydA were subjected to fermentation using 10 g/L (108.7 mmol/L) of glycerol at initial pH 5.8. The recombinant hycE and recombinant hydA showed 41% and 20% higher hydrogen yield compared to wild-type (0.46 ± 0.01 mol/mol glycerol), respectively. The ethanol yield of recombinant hycE (0.50 ± 0.02 mol/mol glycerol) was about 30% lower than wild-type SS1, whereas ethanol yield of recombinant hydA (0.68 ± 0.09 mol/mol glycerol) was comparable to wild-type SS1.

Conclusions: Both hycE and hydA could improve hydrogen yield at initial pH 5.8. The recombinant hydA could retain ethanol yield in spite of high hydrogen yield, suggesting clostridial hydA had an advantage over hycE gene in hydrogen and ethanol co-production under acidic condition. This study could serve as a useful guidance for future development of effective strain co-producing hydrogen and ethanol co-production.