Changes in soil microbial community structure and function associated with degradation and resistance of carbendazim and chlortetracycline during repeated treatments

The degradation characteristics of carbendazim (CBD) and chlortetracycline (CTC) in individual and combined treatments, and dynamics of soil microbial structural and functional diversity as well as their potential relations were studied during three repeated treatments using different concentrations. The results showed that the degradation half-life of CBD at concentrations of 3 mg/kg and 6 mg/kg obviously increased, but that of CTC at levels of 1 mg/kg and 10 mg/kg decreased with increasing treatment frequency. Soil microbial activity and functional diversity displayed the suppression trend in CBD treatment and the suppression-recovery-stimulation trend in CTC and CBD + CTC treatments, which were consistent with the findings of decreased degradation rate of CBD and increased degradation rate of CTC. 16S amplicon sequencing analysis revealed five potentially dominant CTC-resistant microbial genera including Bacillus, Actinobacillus, Pseudomonas, Mycobacterium, and Corynebacterium, which may mainly carry major facilitator superfamily transporter protein, ribosomal protection protein, and other proteins encoded by tetA, tetB, tetC, tetH, tetL, tetM, tetO, tetV, tetW, tetX, tetZ, tet33, and tet39. These five dominant genera may jointly contribute to the elevated bacterial community resistance to CTC. Our findings provided a better understanding of microbial community structure and function changes in repeatedly treated soils with CBD and CTC. © 2016 Elsevier B.V

The effect of ultralow-dose antibiotics exposure on soil nitrate and N2O flux

Exposure to sub-inhibitory concentrations of antibiotics has been shown to alter the metabolic activity of micro-organisms, but the impact on soil denitrification and N2O production has rarely been reported. In this study, incubation and column transport experiments were conducted on soils exposed to as many as four antibiotics in the ng.kg(-1) range (several orders of magnitude below typical exposure rates) to evaluate the impact of ultralow dose exposure on net nitrate losses and soil N2O flux over time. Under anaerobic incubation conditions, three antibiotics produced statistically significant dose response curves in which denitrification was stimulated at some doses and inhibited at others. Sulfamethoxazole in particular had a stimulatory effect at ultralow doses, an effect also evidenced by a near 17% increase in nitrate removal during column transport. Narasin also showed evidence of stimulating denitrification in anaerobic soils within 3 days of exposure, which is concurrent to a statistically significant increase in N2O flux measured over moist soils exposed to similar doses. The observation that even ultralow levels of residual antibiotics may significantly alter the biogeochemical cycle of nitrogen in soil raises a number of concerns pertaining to agriculture, management of nitrogen pollution, and climate change, and warrants additional investigations.Northeast Sustainable Agriculture Research and Education (SARE) program [GNE13-057]SCI(E)[email protected]