Antibiotic Effects on Microbial Communities Responsible for Denitrification and N(2)O Production in Grassland Soils

Antibiotics in soils may affect the structure and function of microbial communities. In this study, we investigated the acute effects of tetracycline on soil microbial community composition and production of nitrous oxide (N(2)O) and dinitrogen (N(2)) as the end-products of denitrification. Grassland soils were pre-incubated with and without tetracycline for 1-week prior to measurements of N(2)O and N(2) production in soil slurries along with the analysis of prokaryotic and fungal communities by quantitative polymerase chain reaction (qPCR) and next-generation sequencing. Abundance and taxonomic composition of bacteria carrying two genotypes of N(2)O reductase genes (nosZ-I and nosZ-II) were evaluated through qPCR and metabolic inference. Soil samples treated with tetracycline generated 12 times more N(2)O, but N(2) production was reduced by 84% compared to the control. In parallel with greater N(2)O production, we observed an increase in the fungi:bacteria ratio and a significant decrease in the abundance of nosZ-II carrying bacteria; nosZ-I abundance was not affected. NosZ-II-carrying Bacillus spp. (Firmicutes) and Anaeromyxobacter spp. (Deltaproteobacteria) were particularly susceptible to tetracycline and may serve as a crucial N(2)O sink in grassland soils. Our study indicates that the introduction of antibiotics to agroecosystems may promote higher N(2)O production due to the inhibitory effects on nosZ-II-carrying communities.