Perfil biotecnológico de microrganismos tolerantes a metais potencialmente tóxicos, capazes de promover crescimento vegetal e remediar resíduos agroindustriais

Abstract

The concern with the most possible sustainable agricultural production, and with the minimization or recycling of residues generated in the different agroindustrial processes, including those of the Brazilian sugar and alcohol sector, has increased in the last two decades. Regarding such residues, they usually have high levels of organic compounds and, according to industrial processes, even some potentially toxic metals, and must undergo treatment before being dispensed. Thus, the search for forms of soil and/or seedlings microbiolization to increase productivity in the field, as well as waste bioremediation, have been targeted ecoefficient alternatives. In this work, high osmotic gradient tolerant bacteria and different concentrations of potentially toxic metal salts (CuSO4, NiSO4 6H2O, CdSO4. 8/3H2O, ZnSO4.7H2O, PbCl2, CoSO4.7H2O, MnSO4. H2O, K2CrO4, and HgCl2), were isolated and evaluated for their enzymatic activity profile (in the presence and absence of the studied metal salts), high temperature tolerance and NaCl concentrations, sensitivity antibiotics (Amikacin, Norfloxacin and Tetracycline), symbiosis type, and finally identified biochemically and molecularly. In addition, it was verified whether the most efficient strains could promote plant growth/germination (Lactuva sativa), secrete biosurfactants / bioemulsifiers and bioremediate sugarcane residues (sludge and effluent). Finally, a low cost formulation was tested to make it possible to apply the microbial pool in vitro and / or under field conditions. Five bacteria tolerant to osmotic gradient and high concentrations of the tested metal salts were selected and they were able to produce enzymes of biotechnological interest. In symbiosis tests, it was shown that the five selected strains can coexist, that is, compose a microbial consortium without antagonizing each other. These were identified biochemically and molecularly as as Pseudomonas aeruginosa - EFI, Bacillus atrophaeus - EFII, B. cereus - EFIII, Lysinibacillus macroides - LOII and B. thuringiensis - LOIII. Except for the P. aeruginosa - EFI isolate, all others are facultative thermophiles and sensitive to the tested antibiotics. Potentially toxic metal salt cultivation did not affect catalase activity, but at high concentrations it affected cytochrome oxidase in L. macroides - LOII, and nitrate reductase in P. aeruginosa - EFI, L. macroides - LOII and B. thuringiensis - LOIII. Only B. atrophaeus - EFII presented both biosurfactant and bioemulsifying capacities under the studied conditions, and was the only one that did not solubilize phosphate in liquid medium. All isolates fixed nitrogen and produced IAA in vitro. Inoculation of lettuce seeds with the consortium also provided high germination rate (97%). The five strains were able to modify in vitro the effluents (synthetic and agroindustrial) and the studied sludge, suggesting their subsequent application in fertigation and soil biosolid, respectively. Under field conditions, the consortium was used to treat effluent from a sugar and alcohol industry, and its efficiency during a harvest-season was also proven (monitoring of different physicochemical parameters), with an average rate of removal of chemical oxygen demand (COD) of 72.50%. Therefore, regarding the studied aspects, the five selected bacteria have potential of biotechnological applications, especially as a supplement for the promotion of plant growth and in the bioremediation of agroindustrial residues.