DNA viral community enhances microbial carbon fixation capacity via auxiliary metabolic genes in contaminated soils

Soil is the largest organic matter repository on land and the virosphere is an essential component of soil carbon cycling. While a few carbon-related auxiliary metabolic genes (AMGs) in viruses are reported to potentially influence the hosts, the effects of virus-host interactions on soil carbon fixation, particularly in carbon-deficient contaminated soils, need further validation. Here, we explore the impact of viruses on carbon fixation in contaminated soils from 58 metal mining areas across eastern China. Eleven different functional categories of carbon fixation AMGs are identified via metagenomic analysis in 323 contaminated soil samples. Enzymatic activities of three key AMGs (i.e., rbcL, ppdK and TKT) are experimentally characterized, indicating the positive role of these genes in carbon fixation. Furthermore, transcriptomic sequencing reveals that after active virus inoculation the carbon fixation genes significantly up-regulate (~73%, p < 0.05). In mesocosms with stable isotope labeling, the accumulation of ¹³C-labeled organic carbon significantly increases (~10%, p < 0.01). Our results provide theoretical and experimental evidence for incorporating viral contributions into the assessments of carbon fixation, and improve the understanding of viral roles within the processes of carbon cycling.