Regulatory mechanism of antioxidant enzymes on microbial metabolism and NADH in anaerobic fermentation of food waste for hydrogen production

Abstract

Anaerobic fermentation is frequently hampered by toxicity arising from oxidative stress, and antioxidant enzymes play a crucial role in combating oxidative stress. In this study, the mechanism of microbial consortium and metabolic pathways regulated by antioxidant enzyme genes in anaerobic fermentation with different pH values was revealed. The results showed that antioxidant enzyme genes, such as glutathione peroxidase, peroxidase, and superoxide dismutase, were 5 times, 3 times, and 2 times higher at pH 7 than at pH 5, respectively. This allowed Clostridium to effectively resist oxidative stress, with substrate metabolism dominated by glycolysis, leading to an increase in the NADH/NAD⁺ ratio. Furthermore, the relative abundance of hydrogenase and electron transfer efficiency increased by 4.5 times and 2.71 times, respectively, resulting in a hydrogen production of 21.48 L/L. When antioxidant enzyme genes were inhibited at pH 5, the substrate mainly produced biomolecules for combating oxidative stress through the pentose phosphate and glycerophospholipid pathways, and led to the transformation of dominant genus into Lactobacillus. With an increased lactate dehydrogenase activity of 5.34 times, the final lactate production reached 65.17 g/L, which was 19.69 times higher than at pH 7. These results elucidate the regulatory mechanism of pH mediated antioxidant enzyme genes on hydrogen production and improve the controllability of anaerobic fermentation.