No Long-Term Persistence of Bacterial Pollution-Induced Community Tolerance in Tylosin-Polluted Soil

Abstract

Pollution-induced community tolerance (PICT) of soil bacteria to the antibiotic tylosin was studied over 95 days. Tylosin was added at increasing concentrations, together with different amounts of alfalfa to study the effects of substrate addition on PICT and bacterial growth in soil. The leucine incorporation technique was used to estimate bacterial growth and as a detection method in the PICT concept. Direct inhibition of the bacterial growth rates, resulting in a dose-response curve, was found above 50 mg of tylosin kg(-1) of soil two days after tylosin addition (IC50 value of 960 mg tylosin kg(-1)). After 10 days of exposure to at least 50 mg of tylosin kg(-1), the PICT was observed and correlated to inhibition of bacterial growth by tylosin. A return of the PICT to control levels was found over time, and after 95 days at 1500 mg of tylosin kg(-1), essentially no PICT was found, as compared to the unpolluted control soil. The return of PICT to pre-exposure levels was not totally reflected in the recovery of bacterial growth. Alfalfa addition did not affect the inhibitory effect of tylosin on bacterial growth rates; neither did it alter the PICT. Since tylosin is relatively rapidly degraded in soil, our results indicate that the PICT will return to prepollution levels when the selective pressure of the toxicant is removed and will thus be a useful technique for monitoring remediation measures.

Use of polar organic chemical integrative samplers to assess the effects of chronic pesticide exposure on biofilms

“…Heterotrophic function was not affected, whereas photosynthesis differed depending on the origin of the biofilm and the level of contamination imposed. All together these results infer that a certain level of pressure has to be reached to induce community tolerance (R/C), and that tolerance would probably not last over long periods in the event of decreasing exposure (C), in accordance with the observations of Aldén Demoling and Bååth (2008) in polluted soils.…”

The Toxicity Exerted by the Antibiotic Sulfadiazine on the Growth of Soil Bacterial Communities May Increase over Time

“…However, in soil 2 (Figure 2), the bacterial community growth decreased for the higher SDZ doses, achieving significant reductions in relation to the control for the doses of 500 and 2000 mg•kg −1 . However, the magnitude of decrease for the highest SDZ dose (2000 mg•kg −1 ) was relatively low (32%), if compared with results previously reported for other antibiotics, such as tylosin [33,41], tetracyclines [22,28,29,33], or streptomycin [22]. It is worth noting that, despite the low adsorption previously reported for SDZ onto soils [42], the short-term effect of SDZ on bacterial community growth was relatively low.…”

Comparative Toxicity of Nanoparticulate CuO and ZnO to Soil Bacterial Communities

“…The sand-toxicant mixtures were mixed into the soil samples through vigorous shaking and stirring with a clean spatula to ensure homogenous application, and all treatments were run in independent duplicates. The samples were incubated for a period of 5–7 h to allow sufficient mixing and equilibration of the sample, yet sufficiently brief to ensure that the innate soil bacterial tolerance to the toxicant additions, rather than the induced tolerance following the selective growth of a tolerant community [12]–[14], [16], were assessed. After this incubation, all samples were analyzed for bacterial growth using the leucine incorporation method [19] adapted for soil [9], [20], importantly using short incubation periods (2 h).…”

“…By measuring the resulting metal concentrations in soil solution, we strengthen the connection between metals and toxicity. To provide a sensitive measure of ecotoxicity we measured the effect of the substance additions on bacterial growth using the leucine incorporation method [9], [10], previously successfully used to accurately determine toxicity of environmental toxicants including metals [11], [12], antibiotics [13]–[15], phenols [16] and salt [17].…”