Metagenomic analysis reveals nonylphenol-shaped acidification and methanogenesis during sludge anaerobic digestion

Nonylphenol (NP) is widely known for its estrogenic activity on organisms, but its influence on biochemical processes executed by complex microbiota is still unclear. The dose-specific effects of NP on sludge anaerobic digestion by shaping acidification and methanogenesis were reported. Both low (50 mg/kg) and high (1000 mg/kg) NP doses were beneficial to acidification and aceticlastic methanogenesis (AM), and high NP dose further stimulated hydrogenotrophic methanogenesis (HM). Stable isotope probing analysis indicated that the predominant methanogenic pathway was shifted from AM to a combination of AM and HM as NP dose increased. Acidogenic and methanogenic consortia were accumulated and restructured by NP in favor of acidification and substrate-based methanogenesis. Acidification-related genes for bioconversion of substrates into acetate (glycolysis, stickland reaction and pyruvate metabolism), acetate transportation and microbial robust performance were enriched with both low and high NP doses. Methanogenesis-related genes encoding acetyl-CoA dehydrogenase/synthetase (CODH/ACS) in aceticlastic pathway and transporters for coenzyme synthesis were enhanced by both NP doses. Besides, high NP dose promoted a majority of genes in CO₂-reduction pathway and key material transporters for coenzyme F420 and heterodisulfide reductase synthesis. This study shed light on complex microbial processes rather than certain organisms affected by NP with dose-specific pattern at genetic level and had implications in resource utilization of sludge containing refractory organics.