Mecanismos de tolerância ao chumbo e resposta ao estresse oxidativo de Bacillus pumilus, rizobactéria isolada de Enydra anagallis

Abstract

Lead is present in the most diverse environmental matrices in trace concentrations, however it is one of the most toxic metals and even at low concentrations can cause problems. In plants, for example, affects germination, stability, growth, water and nutrients absorption, in addition causes oxidative stress. In humans and other animal species, it can accumulate in bones, affect the reproductive and nervous system, among others. In the search for techniques that aim to remove or attenuate this metal to non-harmful levels, the concept of phytoremediation appears as a viable alternative, as it is economical, does not harm the environment and also helps in the revegetation of the site. Thus, this study aimed to evaluate the tolerance of the rhizobacteria Bacillus pumilus, isolated from Enydra anagallis, to lead and the response to oxidative stress of the isolate and the plant species. The plant was collected on the banks of the Santa Bárbara dam (Pelotas, RS). For the study, a microorganism was isolated and selected, which was molecularly identified through 16S DNA as Bacillus pumilus. The activities of the antioxidant enzymes catalase, superoxide dismutase and glutathione peroxidase, the redox state through the reaction to thiobarbituric acid, and the metal removal potential by rhizobacteria were analyzed. According to the results, Bacillus pumilus was resistant to high concentrations of lead (~200 mg/L) and was able to remove the metal from the nutrient broth. Interestingly, the metal did not interfere with the enzymatic activity of the isolate, even at the highest concentration tested. High concentrations of metal were quantified in the roots, leaves and stems of Enydra anagallis, demonstrating that it is a bioaccumulator plant. Likewise, significant concentrations of lead were quantified in the soil and water of the Santa Bárbara dam, values higher than those established by legislation. In the analyzes of enzymatic activity and redox state, the presence of the metal does not seem to interfere with the metabolism of Bacillus pumilus and Enydra anagallis, indicating that, despite the levels of lead found in the environmental matrices and the concentrations tested, the condition of the medium in which they grow found did not constitute a cause of stress in their metabolism, probably because they had developed one or some resistance mechanisms.