RESUMO
The presence of genetic determinants homologous to rulAB genes for ultraviolet (UV) radiation resistance was determined in a collection of Pseudomonas syringae pv. syringae strains isolated from mango. The potential role of these plasmids in UV tolerance and ecological fitness in the mango phyllosphere was also evaluated. Nearly all of the 62-kb plasmids present in the P. syringae pv. syringae strains hybridized with a rulAB probe, but these 62-kb plasmids showed differences in restriction patterns. In vitro assays of tolerance to UV radiation of P. syringae pv. syringae strains showed a higher survival of the strains harboring the 62-kb plasmids compared to strains lacking plasmids when exposed to UVC or UVA+B fractions. Similar results were observed when transconjugants harboring the 62-kb plasmid were tested. Survival assays were carried out under field conditions, and a higher survival of P. syringae pv. syringae strains harboring 62-kb plasmids under direct solar radiation on the adaxial surface of leaves was also observed. When the assays were carried out in shady areas or on the abaxial surface of leaves, survival time was comparable for all the assayed strains, whether or not they contained a 62-kb plasmid hybridizing to rulAB. Our results indicate that P. syringae pv. syringae strains harboring 62-kb plasmids show an increase in ecological fitness when colonizing the mango phyllosphere.
Assuntos
Proteínas de Bactérias/genética , Mangifera/microbiologia , Plasmídeos/genética , Pseudomonas syringae/efeitos da radiação , Tolerância a Radiação/genética , Raios Ultravioleta , Contagem de Colônia Microbiana , Conjugação Genética , Eletroporação , Folhas de Planta/microbiologia , Pseudomonas syringae/genética , Pseudomonas syringae/crescimento & desenvolvimento , Pseudomonas syringae/isolamento & purificação , Luz SolarRESUMO
Heavy metal genotoxicity was evaluated by using different microbial tests. Four genotoxicity assays were employed: the Ames test, the E. coli WP2 test, the Mutatox test detecting mutagenicity, and the SOS assay with E. coli-detecting enzyme induction. All the metals tested (cadmium, chromium, copper, mercury, nickel, and zinc) were detected as genotoxic by the Mutatox and the SOS tests. The Ames test and the E. coli WP2 assay only detected chromium as genotoxic, causing a mutagenic effect. The sensitivity to metals of all the assays used was maintained when they were dissolved in sewage, although there was a slight increase in the sensitivity thresholds.
Assuntos
Escherichia coli/efeitos dos fármacos , Metais/toxicidade , Mutação/efeitos dos fármacos , Salmonella typhimurium/efeitos dos fármacos , Poluentes Químicos da Água/toxicidade , Exposição Ambiental , Escherichia coli/genética , Testes de Mutagenicidade , Mutação/genética , Salmonella typhimurium/genética , EsgotosRESUMO
Heavy metal toxicity was studied by assaying six microbiological toxicity tests, both in solution and wastewater. Pseudomonas fluorescens and baker's yeast (Saccharomyces cerevisiae) were used; growth and respirometric determinations were performed. In addition, the Microtox test was employed as a reference method. The Microtox test is the most sensitive assay for detecting toxicity of zinc, copper, and mercury but not for cadmium, chromium, and nickel. Wastewater increases the sensitivity threshold (EC20) and EC50 values of the metals in most of the assays, which is correlated to the presence of organic and inorganic compounds that can reduce the bioavailability of the metals, leading to a general loss of sensitivity. All the above-mentioned assays are potentially useful in the detection of chemical toxicity of metals. However, each test shows different sensitivities to each metal, which is related to different sensitivities of the organisms used in the assays, as well as to other factors. Therefore, it would be advisable to use a battery of tests for biological evaluation of metal toxicity.
Assuntos
Metais/toxicidade , Pseudomonas fluorescens/efeitos dos fármacos , Saccharomyces cerevisiae/efeitos dos fármacos , Esgotos , Dose Letal Mediana , Testes de Sensibilidade Microbiana , Sensibilidade e EspecificidadeAssuntos
Metais/toxicidade , Consumo de Oxigênio/efeitos dos fármacos , Pseudomonas fluorescens/efeitos dos fármacos , Saccharomyces cerevisiae/efeitos dos fármacos , Cádmio/toxicidade , Cromo/toxicidade , Cobre/toxicidade , Dose Letal Mediana , Pseudomonas fluorescens/fisiologia , Saccharomyces cerevisiae/fisiologia , Sensibilidade e EspecificidadeRESUMO
The resistance patterns of Pseudomonas aeruginosa strains isolated from freshwater and seawater to different antimicrobial agents and heavy metals were studied. It was found that resistance in these environments is linked to the level of faecal pollution. All strains were resistant to ampicillin and tetracycline but sensitive to carbenicillin, amikacin, tobramycin, and colistin, and to the assayed concentrations of silver, cadmium, lead, and molybdenum. Resistance to gentamicin, sulphadiazine, mercury, arsenic, and chromium was variable, so their use as epidemiological markers was considered. There was a close relationship between the degree of pollution and the frequency of heavy metal resistant strains of Ps. aeruginosa. The highest frequencies of resistance to mercury and arsenic were obtained from marine environments with little faecal pollution, where the highest incidence of multi-resistant strains was also observed.