Green-synthesized nickel oxide nanoparticles enhances biohydrogen production of Klebsiella sp. WL1316 using lignocellulosic hydrolysate and its regulatory mechanism

Green synthesis of nickel oxide nanoparticle (NiO-NP) from Eichhornia crassipes (Ec) extract was novelly con-ducted, and regulatory effect of this NP on fermentative hydrogen production was evaluated. Characterization of the Ec-NiO-NP revealed their cubic and spherical shape, small diameter (9.1 +/- 2.6 nm) and high purity. The maximum cumulative hydrogen production and hydrogen yield Y(H-2/S) reached 4842.19 +/- 23.43 mL/L and 101.45 +/- 3.32 mL/g(substrate), respectively, in the presence of 20 mg/L Ec-NiO-NP, which were 47.29% and 37.78% higher than the control without NPs addition. Evaluation of glucose and xylose utilization efficiency as well as key node metabolites further established the potential of Ec-NiO-NP to improve the reducing sugar conversion and metabolic flux distribution in hydrogen synthesis pathway. Furthermore, addition of 20 mg/L Ec-NiO-NP resulted in enhanced hydrogenase activity with a maximum increase of 623% comparing to the control, and led to changes in the gene expression of both hydrogenase and formate-hydrogen lyase, which play important roles in promoting hydrogen production at different stages of fermentation. This study demonstrates that supplementation with green-synthesized Ec-NiO-NP effectively improves fermentative hydrogen production and regulates key node metabolites alteration and functional gene expression.

Automated summary

The green synthesis of nickel oxide nanoparticles from Eichhornia crassipes extract showed promising results in enhancing fermentative hydrogen production by improving reducing sugar conversion and metabolic flux distribution, increasing hydrogenase activity, and altering the expression of key genes.