This study investigated the role of mesophilic and thermophilic bacteria and their viruses in nutrient cycling during industrial-scale hyperthermophilic composting (HTC). Using metagenomics and metatranscriptomics with temporal sampling, the researchers found a tight coupling between virus-bacteria density dynamics and activity. Viruses specific to mesophilic and thermophilic bacteria tracked their host densities, driving microbial community succession. Mesophilic bacteria-specific viruses encoded and expressed auxiliary metabolic genes (AMGs) linked to carbon cycling, impacting nutrient turnover. Nutrient turnover correlated positively with the virus-host ratio, indicating a positive relationship between ecosystem functioning, viral abundances, and activity. DNA viruses were the primary drivers of these effects, while RNA viruses were mainly associated with eukaryotes and not linked to nutrient cycling during the thermophilic phase. The findings suggest that DNA viruses drive nutrient cycling in HTC through biomass recycling and AMG expression, potentially serving as indicators of microbial ecosystem functioning.
