New insight on Fe-bioavailability: Bio-uptake, utilization and induce in optimizing methane production in anaerobic digestion

Fe-bioavailability is an essential factor affecting CH4 production from anaerobic digestion (AD). However, the actual uptake and utilization process of iron in complex microbial communities remains unclear. In this study, the effects of Fe-bioavailability in six iron dosages on CH4 production were compared. The results showed that CH4 production increased to 144.37 mL CH4/g COD (154.1% higher than the control group) when dosing is 50 mg/L with the best Fe-bioavailability (3.125 mg Fe/g TS). Flow cytometry and enzyme analysis further demonstrated that the reactor with the highest Fe-bioavailability had the protective mechanism of ferroptosis and the highest living cell and DNA content. Metagenomic analysis of microbial communities and metabolic pathways revealed the potential pathways of iron bio-utilization in pyruvate metabolism dominant by Candidatus Cloacamonas Acidaminovorans and methane metabolism dominant by acetophilic methanogens were improved. In view of the significant improvement of lipopolysaccharide biosynthesis, the two-component system, ABC transporter, quorum-sensing, and ribosome metabolic pathways, it can propose that iron-induced signaling molecule accelerates matter and energy exchange on the membrane, thus enhancing the microbial function of the anaerobic system. This study revealed the process of iron uptake and utilization by microbial communities and the potential mechanism of promoting interspecific iron uptake, improving the carbon conversion efficiency of organic matter in AD.