Resumo

The contamination of soils and water bodies by heavy metals constitutes another great environmental challenge, which can be aggravated by the application of fertilizers, sewage sludge and industrial residues, and animals constitute the main source of trace elements. In most cases, soil contamination by metals is associated with more than one element, but interactions between metal contaminants and microorganisms are frequent and intense in the soil. Thus the objective of this study was to determine the influence of different concentrations of heavy metals on the growth and methylmercury removal capacity by P. putida V1 under in vitro conditions. To determine the growth of P. putida V1 in the presence of the metals: copper, nickel, chromium and lead after 48 hours at 29ºC. In order to evaluate the combined influence of the metals (copper, lead, nickel and chromium) on the growth of P. putida V1, 2.5 µmol/L of methylmercury was added to the LB medium. All the tubes were incubated at 29ºC, and cell growth was determined from the optical density (OD600 nm) in a Spectronic-20, GENESYSTM spectrophotometer. LB broth inoculated with P. putida V1, but without the addition of any of the metals or methylmercury, was used as the positive control, and tubes containing the different metals and methylmercury, but not inoculated with P. putida V1, constituted the negative controls. The methylmercury removal capacity of P. putida V1 from LB broth, the concentration of methylmercury added to the LB broth was 0.008 µmol/L, since previous experiments indicated that a concentration of 2.5 µmol/L resulted in death of the P. putida V1. Before the cold steam mercury analysis, the samples were digested by methods EPA 245.1. Although the concentrations of heavy metals tested were in the average range found in contaminated environments, it was observed in the present study that the methylmercury concentration was determinant for survival of the microorganisms. Despite the fact that the heavy metals studied influenced the growth and removal of methylmercury by P.putida V1, the concentration of the methylmercury was determinant for the survival of the bacterium.