Mechanisms of Ofloxacin Exposure Inhibiting Hydrogen Production in Anaerobic Fermentation

Ofloxacin (OFL) exists widely in raw materials of organic fermentation, which can inhibit hydrogen production of dark fermentation. In this study, the inhibition of OFL on hydrogen production was studied from the aspects of hydrogen production performance, bacterial community and functional genes using glucose as a model substrate. The results showed that OFL exposure ≥ 10 mg/L significantly decreased the hydrogen production. With an OFL exposure concentration of 500 mg/L, the hydrogen yield reduced to 48.35 ± 2.13 mL/g glucose and the lag period prolonged to 26.48 ± 0.40 h, compared with those of control without ofloxacin exposure (169.99 ± 9.68 mL/g glucose and 8.98 ± 0.07 h), respectively. The efficient hydrogen-producing bacteria, Clostridium, were inhibited and the dominant microbial population was transformed, leading to change in metabolic pathway of fermentation from butyric acid type to ethanol type. Correspondingly, the proportion of butyrate in metabolites decreased from 66.46% to 0.00%, the proportion of acetate decreased from 26.12% to 3.69%, and the proportion of ethanol increased from 3.13% to 96.31%. OFL exposure showed significant downregulation of predicted functional genes involved in glycolysis and hydrogen production, such as K00845, K00532, and K03737, fundamentally resulting in significant inhibition of glycolysis and pyruvate metabolism for hydrogen production.