Phage‐bacterium interactions and nutrient availability can shape C and N retention in microbial biomass

Phage-bacterium interactions influence soil microbial life and ecological functions, including microbial evolution, community patterns, and nutrient cycling. However, understanding of phage-mediated soil bacterial lysis dynamics, and impacts on soil carbon (C) and nitrogen (N) cycling, remains elusive. Here, we used a short-term laboratory incubation microcosm model system (which did not contain actual soil) consisting of a soil bacterium Bacillus cereus LB2 and an exclusive B. cereus phage SWEP1 to illustrate how a single soil phage manipulates bacterial lysis and the associated necromass formation under different nutrient conditions, and the associated changes on C and N dynamics. Results showed that the phage-induced bacterial lysis significantly increased the total amounts of necromass C and N, which was correlated to nutrient conditions. Bacteria populations were effectively eliminated by phages under eutrophic conditions, whereas the lysis rate of SWEP1 slowed down under oligotrophic conditions. The presence of phage clearly stimulated necromass accumulation, albeit with a reduced proportion of dissolved NH4+-N content from the supernatant. Therefore, phages may enhance microbial necromass formation, and actively contribute to soil organic matter (SOM) stabilisation and C and N cycling in soil ecosystem. Highlights Phage-mediated bacterial lysis increased C and N contents in necromass Eutrophic conditions facilitate phage-mediated bacteria elimination The lysis rate of phage slows down under oligotrophic conditions The contribution of bacterial necromass to SOM may be underestimated