Phages Affect Soil Dissolved Organic Matter Mineralization by Shaping Bacterial Communities

Viruses are considered to regulate bacterial communities and terrestrial nutrient cycling, yet their effects on bacterial metabolism and the mechanisms of carbon (C) dynamics during dissolved organic matter (DOM) mineralization remain unknown. Here, we added active and inactive bacteriophages (phages) to soil DOM with original bacterial communities and incubated them at 18 or 23 °C for 35 days. Phages initially (1–4 days) reduced CO2 efflux rate by 13-21% at 18 °C and 3–30% at 23 °C but significantly (p < 0.05) increased by 4–29% at 18 °C and 9–41% at 23 °C after 6 days, raising cumulative CO2 emissions by 14% at 18 °C and 21% at 23 °C. Phages decreased dominant bacterial taxa and increased bacterial community diversity (consistent with a "cull-the-winner" dynamic), thus altering the predicted microbiome functions. Specifically, phages enriched some taxa (such as Pseudomonas, Anaerocolumna, and Caulobacter) involved in degrading complex compounds and consequently promoted functions related to C cycling. Higher temperature facilitated phage-bacteria interactions, increased bacterial diversity, and enzyme activities, boosting DOM mineralization by 16%. Collectively, phages impact soil DOM mineralization by shifting microbial communities and functions, with moderate temperature changes modulating the magnitude of these processes but not qualitatively altering their behavior.