Functional Microbial Communities in the Hydrolysis-Acidogenesis Stage Promote Sludge Viral Inactivation under Anaerobic Digestion

The sludge produced in biological wastewater treatment enriches enormous viruses, and the pathogens inactivation is vitally important for protecting public and ecosystem health. Anaerobic digestion (AD) is an ideal bio-stabilization technology to reduce sludge volume and convert nutrients into valuable products, but the compositional variation and host-connections of viruses in sludge during AD process remains poorly explored. Herein, we reported differences in the viral and bacterial microbiomes of sludge subjected to three stages of hydrolysis, acidogenesis and methanogenesis in AD system. As results, the dominant identified viromes phylum associated with animal/plant as hosts were Nucleocytoviricota, Pisuviricota and Preplasmiviricota excepted for phages in AD system; and the metatranscriptome combined with key species-virus activity correlation analysis revealed these viral community inactivation was positively correlated to phyla of Bacillota, Actinobacteria Bacteroidetes and Proteobacteria. Thus, the enzymes of cellulase, proteases and lipases were possible key factors in viral inactivation, which would be increased by secreting of Bacillota and Actinomycetota in hydrolysis-acidogenesis stages, leading to higher virus inactivation via membrane proteins destruction; while enhanced activities of methanogens communities in methanogenesis stage completed and suppressed the Bacillota activities, resulted in viral genes replication and higher residual viral abundance in sludge. These findings gave more insights of relationships between functional microbiome and viral survival in sludge of AD process, and provided important scientific guidance in regulating microbial community structure of AD system to ensure the safe management of sludge in pandemic emergencies.