Prospecção e identificação molecular de bactérias de solo tolerantes a herbicidas com potencial para sua degradação e promoção de crescimento vegetal

Abstract

Brazil is the world leader in production of sugarcane (Saccharum spp.), being ranked among the top manufacturers, consumers and exporters of sugar and ethanol in the international market. Plant production is totally dependent on soil, water, essential minerals and phytohormones, being essential to preserve these resources. In soil, the microorganisms can degrade compounds used for protecting agricultural crops, as well as assist in plant growth, as in the solubilization of phosphates and production of organic acids and auxins. Formulations based on plant growth-promoting bacteria (PGPB) result in increased agricultural production and are an eco-efficient tool of management, especially in soil that is degraded or has received a xenobiotic load for many years, which may affect several forms of life beyond the target organisms. This study aimed to: 1) isolating and identifying bacterial species of land cultivated for more than 40 years with sugarcane, able to tolerate high concentrations of three of the main herbicides with high persistence used on this crop (diuron, sulfentrazone and isoxaflutole); 2) evaluate the growth kinetics of selected isolates on minimal medium containing high concentrations of herbicides; 3) analyze the potential of these isolates in solubilize phosphate and produce indole acetic acid; 4) evaluate the effect of selected isolates on germination and pre-emergence corn seedlings. Among the 96 isolates obtained, four were selected for their ability to grow on solid minimal medium containing up to 1000 μg.mL-1 of these herbicides as a carbon source, and for degrading different organic compounds, including some recalcitrant, in vitro. They were identified as Bacillus toyonensis, Alcaligenes faecalis, B. megaterium and Lysininbacillus macroides, with the latter two show better tolerance and degradation of the three herbicides (especially 10 g.mL-1). B. megaterium and A. faecalis were able to solubilize high concentrations of insoluble phosphate, and they also produce auxin in the presence of herbicides. However, only L. macroides favored corn seed germination in the presence of isoxaflutole and sulfentrazone. Studies of other variables are needed, including of formulations and consortia of such microorganisms, before recommending their use to the remediation of soil with residues of herbicides, among other problems, and to promote plant growth.