Sistemas de respostas antioxidantes ao estresse gerado por Heat em linhagem bacteriana de solo agrícola independente de pressão seletiva prévia por esse herbicida

Abstract

In conventional systems, the use of herbicides has become essential in agriculture to maintain production. In contrast, these substances causing oxidative stress in non-target microorganisms, tolerant phenotypes. Few studies have investigated whether microorganisms can survive against herbicides without prior selection, and it is still unclear whether the mechanisms that involve tolerance will be selected. Thus, this work evaluated whether Stenotrophomonas sp. CMA26, a Heat tolerant strain with no history of prior exposure to this herbicide, may have response systems to support in greater than those used in agriculture. The CMA26 strain was subjected to oxidative stress tests, as tolerance, growth curve, the quantification of peroxide and malondialdehyde. Also was evaluated the response systems, represented by degradation capacity and activity of antioxidant enzymes catalase and glutathione S-transferase, against the herbicide Heat at the concentration equivalent to that used in the field, as well as at 10 and 50 times that concentration. The results indicated that the CMA26 strain has a temporary stress condition in early growth periods, which was overcome by activating and modulating the activities of catalase and glutathione S-transferase enzymes. The tolerance to different levels of heat, as well as the absence of herbicide degradation by the CMA26 lineage and by others granted from the same environment, seems to indicate that the first is related to a generalized enzymatic response, independent of previous selection, and the second is possible a dependent selection process. These combined mechanisms will be found in other microorganisms, since in soil, pesticides may be directing the selection of tolerant microorganisms, but not degrading ones, impacting the population structure and functionality of the microbiota. In reducing degradation, pesticides may be remaining in the soil as environmental contaminants, and reach aquatic environments by drift.