Influence of manure from pigs fed chlortetracycline as growth promotant on soil microbial community structure

Chlortetracycline (CTC), an antimicrobial compound used in animal production, is not sorbed or degraded in the animal, and may enter the field environment through manure land-spreading. This study determined the influence of a single application of manure with or without CTC on field soil microbial community characteristics. Manures from swine fed unamended or CTC-amended rations were applied at 7,000 kg solid ha(-1) to a Brandt silty clay loam soil that had no known prior history of manure application. Soil samples taken 1, 7, 28, or 42 days after treatment (DAT) were analyzed for aerobic culturable counts on R2A agar and most probable number using 2,4-D as sole carbon source. Soil extracts of 1, 7, and 42 DAT samples were subjected to polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) analysis of the V3 region of the 16S rRNA gene pool. Gels were analyzed by Neighbor Joining based on Euclidean distance and Raup-Crick multivariate statistical analysis, and selected bands were extracted to identify predominant community members. Both manure applications initially changed soil microbial diversity, however, communities appeared to converge over time, so that no long-term significant effect was detected with this single application.