SEARCH FOR BIOLOGICAL SURFACTANTS IN HALOPHILIC BACTERIA

FABIANA L MARTÍNEZ; MARTA F LOPEZ; VERÓNICA IRAZUSTA; VERÓNICA RAJAL

Congreso; XII Congreso Argentino de Microbiología General; 2017

Biological surfactants are secondary metabolites of amphipathic nature that lower the surface tension of solutions allowing the formation and stabilization of heterogeneous systems such as emulsions. Halophilic and/or halotolerant microorganisms have the ability to grow in extreme environments using adaptations that allow them to withstand osmotic stress, being the production of biosurfactants one of those strategies. Physicochemical characteristics of these biomolecules allow them to be used in a variety of applications such as in bioremediation, industrial processes, medicine, and biological control.The aim of this work was to search for halophilic and/or halotolerant bacteria that produce biosurfactant molecules for future applications in different bioremediation strategies.Water and soil samples were taken from El Salar de Hombre Muerto, located in the Puna of Atacama in the limit between Catamarca and Salta provinces. A total of 106 bacterial strains were isolated and their ability to grow in defined medium (DM: L- asparragina, 0.5 g/L; K2HPO4, 0.5 g/L; 0,28 ml/L micronutrient solution (FeSO4.7H2O, 0.01 g/L; MgSO4.7H2O, 0.2 g/L) and glucose, 10.0 g/L) without or with the addition of 2 M (DM2) and 4 M (DM4) NaCl, were tested. Hemolytic capacity of strains was studied using blood agar medium as a preliminary evaluation of biosurfactant activity. After 48 h bacteria's ability to lyse partially (alpha hydrolysis) or totally (beta hydrolysis) red blood cells was evaluated. A quantitative evaluation of biosurfactant activity was then performed. For that, 700 µl of culture of each strain grown in DM, DM2, and DM4 for 24 h (30 °C and 250 rpm) were mixed with 700 μl of kerosene. The mixture was mixed-vortex for 1 minute and 1 hour and 24 h after shaking the height of the emulsion formed was measured in order to evaluate its stability. The emulsion index was calculated as the quotient between the height of emulsion and the total height of liquid in the tube.As a result of this work, we observed that 67% of the strains studied had capacity to perform hemolysis of the red blood cells, indicating the ability of isolated bacteria to produce bioemulsifiers. Twenty nine strains presented alpha hemolysis and 42 strains beta hemolysis. These results were in agreement with the quantitative test, where 75 strains presented emulsifying capacity after 1 h, whereas only 42 of those showed stability after 24 h. The emulsion index varied from 2 to 52%. Based on the results obtained in the present work it can be concluded that the microorganisms isolated from El Salar del Hombre Muerto have the capacity to produce biosurfactants, which should be characterized in the following investigations.