Resumo

The enrichment with salts can interfere in the activity of the microbial flora present in ecosystems, such contamination representing a great environmental problem in various parts of the world. The enrichment with salts can result, for example in the case of soils, in great degradation phenomena, such as dispersion, structural loss and reduction in agricultural productivity, also affecting the activity of the soil microorganisms. The principal salts used in agriculture are the following: nitrate, sulfate, phosphate and molybdate. Thus, the objectives of this study were evaluate the influence of the presence of salts (nitrate, phosphate, sulfate and molybdate), on the growth and methylmercury removal capacity of P. putida V1 under in vitro conditions. A methylmercury-resistant isolate of Pseudomonas (P. putida V1), obtained from a soil sample from a landfarming site at the petrochemical pole in Triunfo, RS, Brazil, was used in this study. The effects of the presence nitrate, sulfate, phosphate and molybdate on the growth and methylmercury removal capacity of P. putida V1 were determined using LB broth with the following concentrations of each salt: 50, 100, 200 and 300 mmol/L and 2.5 µmol/L de methylmercury. Tubes containing the different salts and methylmercury, but not inoculated with P. putida V1, constituted the negative controls. All the tubes were incubated at 29ºC, and cell growth was determined from the optical density (OD600 nm) in a Spectronic-20, GENESYSTM spectrophotometer. After 24 hours of incubation, they were placed in the gas exhaustion chamber to remove the volatile Hg, remaining there for 10 minutes. Before the cold steam mercury analysis, the samples were digested by methods EPA 7471B. As compared to the control, the results indicated a significant decline in the methylmercury removal capacity from the LB broth (p<0.05) in the presence of the salts concentrations tested. Although the methylmercury removal capacity of P. putida V1 was negatively affected by the addition of salts (nitrate, phosphate, sulfate and molybdate) to the LB broth, as compared to the control (0), it was not affected by the variation in concentration of these salts (50-300 mmol/L).