Inhibition of Norfloxacin on Fermentative Hydrogen Production: Performance Evaluation and Metagenomic Analysis

Abstract

Toxic chemicals can inhibit the dark fermentation process for renewable biohydrogen production. Norfloxacin (NOR), a typical antibiotic, is present in various feedstocks of dark fermentation. However, current understanding on its impact on fermentative hydrogen production is scare. This study investigated the potential inhibitory impact and mechanism of NOR on fermentative bioH2 production. The results showed that NOR significantly reduced the H2-producing capacity at exposure concentrations more than 10 mg/L. The hydrogen yield decreased from 1.56 to 0.27 H2/mol-glucose at NOR of 50 mg/L. Bacterial community analysis revealed that NOR resulted in a decrease in the abundance of high-yielding H2-generating bacteria, such as Clostridium sp., while increased the abundance of H2-consumuing bacteria (e.g. Enterococcus sp.). Metagenomics analysis further indicated that the genes related to glycolysis (e.g. HK, tal-pgi, pfk, PK and gpml) and the genes encoding key enzymes involved in hydrogen production (e.g. NADH-ferredoxin oxidoreductase, pyruvate-ferredoxin oxidoreductase and ferredoxin hydrogenase) were remarkably down-regulated under NOR exposure, essentially casing the inhibition of H2 production. The present work would contribute to a better understanding of how antibiotics inhibit bioH2 fermentation, and provide theoretical basis for reducing the potential inhibitory effect.

Keywords: Dark H2 fermentation, Norfloxacin, Inhibition, bacterial community, Metagenomic analysis