Abstract
BackgroundAs a renewable and clean energy carrier, the production of biohydrogen from low-value feedstock such as lignocellulose has increasingly garnered interest. The NADH-dependent reduced ferredoxin:NADP+ oxidoreductase (NfnAB) complex catalyzes electron transfer between reduced ferredoxin and NAD(P)+, which is critical for production of NAD(P)H-dependent products such as hydrogen and ethanol. In this study, the effects on end-product formation of deletion of nfnAB from Thermoanaerobacterium aotearoense SCUT27 were investigated.ResultsCompared with the parental strain, the NADH/NAD+ ratio in the ∆nfnAB mutant was increased. The concentration of hydrogen and ethanol produced increased by (41.1 ± 2.37)% (p < 0.01) and (13.24 ± 1.12)% (p < 0.01), respectively, while the lactic acid concentration decreased by (11.88 ± 0.96)% (p < 0.01) when the ∆nfnAB mutant used glucose as sole carbon source. No obvious inhibition effect was observed for either SCUT27 or SCUT27/∆nfnAB when six types of lignocellulose hydrolysate pretreated with dilute acid were used for hydrogen production. Notably, the SCUT27/∆nfnAB mutant produced 190.63–209.31 mmol/L hydrogen, with a yield of 1.66–1.77 mol/mol and productivity of 12.71–13.95 mmol/L h from nonsterilized rice straw and corn cob hydrolysates pretreated with dilute acid.ConclusionsThe T. aotearoense SCUT27/∆nfnAB mutant showed higher hydrogen yield and productivity compared with those of the parental strain. Hence, we demonstrate that deletion of nfnAB from T. aotearoense SCUT27 is an effective approach to improve hydrogen production by redirecting the electron flux, and SCUT27/∆nfnAB is a promising candidate strain for efficient biohydrogen production from lignocellulosic hydrolysates.
Highlights
As a renewable and clean energy carrier, the production of biohydrogen from low-value feedstock such as lignocellulose has increasingly garnered interest
Hydrogen production using various substrates and intracellular NADH/NAD+ ratio of ∆nfnAB mutants To evaluate the effect of deletion of nfnAB on endproduct formation, batch fermentation was first performed in serum bottles with glucose, xylose or glucose/xylose mixture as the substrate
When SCUT27/∆nfnAB and its parental strain SCUT27 were inoculated into fresh MTC medium (10 g/L total sugar), no obvious difference was observed in sugar use and acetic acid formation (Fig. 2, Table 1, Additional file 1: Tables S1, S2)
Summary
As a renewable and clean energy carrier, the production of biohydrogen from low-value feedstock such as lignocellulose has increasingly garnered interest. The concentration of hydrogen and ethanol produced increased by (41.1 ± 2.37)% (p < 0.01) and (13.24 ± 1.12)% (p < 0.01), respectively, while the lactic acid concentration decreased by (11.88 ± 0.96)% (p < 0.01) when the ∆nfnAB mutant used glucose as sole carbon source. The SCUT27/∆nfnAB mutant produced 190.63–209.31 mmol/L hydrogen, with a yield of 1.66–1.77 mol/mol and productivity of 12.71–13.95 mmol/L h from nonsterilized rice straw and corn cob hydrolysates pretreated with dilute acid. Fossil fuels such as natural gas, coal and petroleum have dominated the energy supply for long time. As shown in Eqs. 1 and 2, 4 and 2 mol H2 could be produced from 1 mol glucose when the volatile fatty acids are acetic acid and butyric acid, respectively
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