Bacteria play a more important role than nutrients in the accumulation of tetracycline resistance in manure-treated soil

Abstract

Manure application to agricultural soils can increase the abundance of antibiotic-resistance genes and resistant bacterial populations in soil. The aim of this study was to compare the contribution of nutrients and microorganisms of manure in the accumulation of tetracycline resistance in manure-treated soil. Soil microcosms were incubated for 77 days in a bench-scale mesocosm experiment and for 2 years in a greenhouse experiment and treated with manure or sterilized manure. In the manured soil, both aerobic tetracycline-resistant bacteria (TRB) and tetracycline-resistance genes (TRGs) (tetG, tetB(P), tetO, and tetL) were detected. Nutrients and TRGs not carried by live bacteria contribute little to the accumulation of TRB and TRGs, while microorganisms from manure contributed considerably. However, in soil with a long history of manure fertilization, the survival or dissemination of TRB and TRGs were prevented. The native soil microbial communities were probably more competitive than microbial species added with manure for nutrients of colonizing soil niches. Some bacterial species showed a significant negative correlation with the relative abundance of the four TRGs and TRB; probably, these bacterial species might have played a role in inhibiting the survival of TRB or dissemination of TRGs. These findings provide some clues for revealing the mechanisms of how manure application influences the abundance of TRGs and TRB in soil.