Targeting regulation of nitrate removal and chlorophenol degradation through hydrogen/oxygen switching

Nitrate is a common co-contaminant with 2,4-dichlorophenol (2,4-DCP) in water, presenting a challenge for environmental remediation. Under anaerobic conditions, the ring cleavage of chlorophenol is inefficient, while under aerobic conditions, nitrate removal is hindered. In this study, a microbial consortium capable of hydrogenotrophic denitrification and 2,4-DCP degradation was cultured, aiming to achieve efficient nitrate removal and 2,4-DCP degradation by alternately switching between hydrogen (H₂) and oxygen (O₂). Under H₂ conditions, nitrate removal exceeded 90 %, while under O₂ conditions, 2,4-DCP degradation reached 100 %. Under H₂ conditions, the abundance of the Nar gene which was involved in nitrate reduction was higher than that under O₂ conditions, promoting hydrogenotrophic denitrification. In contrast, under O₂ conditions, 2,4-DCP degradation occurred via hydroxylation, ring-cleavage, dechlorination, and mineralization through the TCA cycle. Metagenomic and metabolomic analysis was performed to explore microbial metabolic pathways and potential synergistic mechanisms involved in hydrogenotrophic denitrification and 2,4-DCP biodegradation. In the H₂-atmosphere, microbes (Methylobacillus and Chromobacterium), genes (E3.1.1.45 and speG), and metabolites (Cytosine and Uridine) may play a crucial role in hydrogenotrophic denitrification. In the O₂-atmosphere, the functional genus of Paracoccus and Aquamicrobium associated with genes (tfdB and tfdC) may contribute to 2,4-DCP and its metabolites 2-Chloromaleylacetate degradation. These findings confirmed the role of functional microbial communities through H₂/O₂ regulation. This work provides a promising technological reference for treating industrial wastewater containing phenols and nitrogen.