Bioprospecção de bactérias produtoras de biossurfactante em substratos alternativos

Abstract

Biosurfactants are metabolic products of yeasts, fungi and bacteria that have high emulsifying capacity and the ability to reduce the surface and interfacial tensions. They have several advantages when compared to chemical surfactants, such as their stability to high temperature, pH and salinity, as well as biodegradability and low toxicity. The use of alternative carbon sources such as agroindustrial wastes for their production is an option to reduce the high costs attached and the environmental impact of the poor disposal of these wastes in the environment. The aim of this work was to select biosurfactant-producing bacteria, to evaluate the production from different substrates as well as to verify the stability of the produced biosurfactant and its application for oil removal from contaminated soil. Twenty bacteria isolated from a sugar-alcohol agroindustry were tested, eight of which were isolated from the soil and twelve isolated from the agroindustrial residue called filter cake. After the selection of the bacteria, the carbon and nitrogen sources were evaluated for the production of biosurfactants. Thus, five substrates were used: cane molasses, vinasse, cassava wastewater, coconut pulp and soybean oil as inductor, and four nitrogen sources: urea, yeast extract, sodium nitrate and ammonium sulfate. A 23factorial experimental design with three replications at central point was carried out in order to evaluate the influence of nitrogen source concentration, aeration and inductor ratio on cell concentration, reduction of surface tension and emulsification index in soybean oil and kerosene. The stability of the cell free broth was tested in terms of temperature (100°C e 120°C), salinity (0-14% m/v) and pH (2-8). The obtained biosurfactant was applied in tests of motor oil removal from contaminated sand. The best results were obtained with the bacteria JS20, isolated from soil. The final surface tension in a medium composed of glucose supplemented with residual soybean oil was 40.56 mN/m and emulsion index of 96.10 in motor oil; in a medium composed of molasses and residual soybean oil, the surface tension was 49.57 mN/m. For carbon and nitrogen sources, the best results were those obtained from cell growth and emulsion index. The medium formulated with molassesas carbon source supplemented with residual soybean oil or coconut pulp as inductor and using ammonium sulfate as nitrogen source were the ones that showed the best emulsification index (IE motor oil = 100%; IE soybean oil = 51%; IEkerosene=42.31%). The results obtained in the experimental design showed that the best condition for the production of biosurfactants was in medium composed of molasses (10 g/L of reducing sugars) supplemented with coconut pulp (20 g/L), 1 g/L of ammonium sulfate and 0.67 of aeration ratio. In this condition, it was obtained 100% of emulsion index in motor oil and 50% in kerosene. The cell free crude broth was stable over a wide range of pH, temperature and salinity. In oil removal from contaminated sand tests, it was possible to achieve a percentage removal of 78.71%.