Effects of chlortetracycline on soil microbial communities: Comparisons of enzyme activities to the functional diversity via Biolog EcoPlates™

Abstract

Veterinary antibiotics (VAs) can enter agricultural soil by the application of animal excrements. However, the response of soil microorganisms to VAs is not well understood. Therefore, a 45-day microcosm experiment was conducted to ascertain the impact of chlortetracycline (CTC) on soil microbial communities. In this study, CTC was applied to soil samples with no previous antibiotic-containing manure application history at three concentrations of 1, 10, and 100 mg/kg soil. Soil samples were taken after 1, 6, 12 and 45 day(s) of incubation to determine the dissipation of CTC using HPLC. Meanwhile, to investigate the effect of CTC on microorganisms, microbial activities in the cultivable and the actual community were determined using Biolog EcoPlates™ and enzyme activities, respectively. It was demonstrated that CTC dissipated faster at lower spiking levels. At the end of the experiment, no CTC could be extracted in all treatments, except for C100. The enzyme activities were enhanced on the first day and then were significantly inhibited by CTC for up to 45 days. This inhibition was especially true for activities of dehydrogenase and urease, whereas phosphatase activities were slightly affected. The results demonstrated that CTC contamination could pose a selective pressure on soil microorganisms, despite its rapid decline in the extractable concentration. However, community-level physiological profiles (CLPP) that were assessed using Biolog EcoPlates™ displayed different susceptibilities to the addition of CTC: it responded rapidly to CTC-amendment and were improved strongly by CTC on the first day, whereas no effect was detected thereafter. It was suggested that the Biolog EcoPlates method was more suitable for short-term toxicity tests than for the relatively long-term effects of pollutants on microbial communities.