Ferroferric oxide promotes metabolism in Anaerolineae other than microbial syntrophy in anaerobic methanogenesis of antibiotic fermentation residue

Abstract

Antibiotic fermentation residue (AFR) is a kind of protein-rich biosolids that would be utilized as valuable substrates for biogas production. However, the effectiveness of conductive material supplementation and its effect on the microbiome in anaerobic digestion of AFR have not been fully elucidated. The objective of this study is to access the impact of Fe3O4 addition on anaerobic digestion of AFR and reveal its microbial mechanism. By adding Fe3O4 at concentration of 150 mg/gTS to two typical AFRs, the methane yield was decreased while the methane production rate was significantly enhanced by 48% and 21%, respectively. Genomic analyses revealed that the Fe3O4 addition altered the microbial community by selecting the unknown genus of Anaerolineae with the metabolic capacity of carbohydrate hydrolysis and proteolysis. Meanwhile, the hydrogenotrophic methanogenesis was the dominant pathway in the AFR digestion system, which was mostly contributed by the Methanoculleus and Methanolinea. More interestingly, Methanoculleus might possess fermentative capability involved in the versatile hydrolysis pathway. Although the genes related to electrically conductive pili were detected, the induction of direct interspecies electron transfer by Fe3O4 supplementation was not confirmed in this study. In summary, except the accelerated methane production rate, Fe3O4 addition functioned as biostimulator for Anaerolineae other than electron conduit in anaerobic methanogenesis in the AFR digestion system.