Biodegradação do herbicida mesotrione por linhagens bacterianas isoladas de folhas de milho

Abstract

Chemical fertilizers and pesticides have become an important part of modern agriculture. The use of these chemical brought great benefits but also created new problems, such as disposal after use, persistence over time and accumulation in the environment, resulting significant bad consequences to public health and adverse impact on ecosystems. Maize culture deserves attention because the large amount of herbicides used. Mesotrione is a new selective herbicide developed for use in maize culture. Due it has not been used for a long time, there is little information available on the ecotoxicological risk. Only two mesotrione-degrading strains, from soil and water, both the genus Bacillus, were isolated and identified. The aim of this study was to isolate and characterize endophytic and epiphytic bacterial strains collected from maize leaves, able to biodegrade the herbicide mesotrione. Samples were collected in maize planting variety Penta without treatment with mesotrione and maize planting variety DKB 234 treated with mesotrione, at Fazenda Escola Capão da Onça, Ponta Grossa, PR. The microorganisms were isolated and cultured in mineral medium supplemented with mesotrione as sole carbon source. Of the twenty samples were isolated 347 tolerant and/or mesotrione-degrading strains. These were selected in increasing concentrations of the herbicide and had their degradation capability evalueted by VIS spectrophotometry. Ten strains were able to grow in the presence of high concentrations of mesotrione. Of these, 9 strains (7 epiphytic and 2 endophytic) were isolated from maize variety Penta without treatment with mesotrione and only 1 epiphytic strain was isolated from maize variety DKB 234 treated with mesotrione. Five strains had the ability to degrade the herbicide confirmed. One strain was identified as Acinetobacter baumanii and other as Micrococcus luteus. Just M. luteus is an endophytic strain, the others are maize epiphytics. Four mesotrione-degrading strains were isolated from maize untreated with mesotrione, only one strain of Gram-negative bacilli non fermenter was isolated from maize treated with the herbicide. The growth in high concentration of the strains that didn’t have the mesotrione degradation capability detected by spectrophotometry indicates the possibility of these strains degrade this herbicide when in association with other microorganisms consortia in the environment. The real quantitative capability of mesotrione degradation by the strains recorded by spectrophotometry may be underestimated due to the accumulation of degradation products which have the same wavelength as the mesotrione. This study reports the first isolation and characterization of mesotrione degrading strains endophytic and epiphytic from maize.