ISOLATION AND SCREENING BIOSURFACTANT (BS) PRODUCING BACTERIA

Abstract

There are two broad classes of surfactants: chemically synthesized surfactants andbiologically synthesized surfactants - biosurfactants (BS). BS have potentials of their broadrange of industrial application and have several advantages over the chemical surfactants. Inmany areas of industrial applications, chemical surfactants have subtituted by BS. From soil, grass, food, raw oil samples we isolated 59 strains of Bacillus and Pseudomonas. Oil displacement of every isolate was checked. Crude oil  was put onto the surface of 40 mlof distilled water in petri dish. Then of the culture sample solution was gentlyput on the center of the oil membrane. Area of clear halo was calculated. From 59 tested isolates, 12 strains have oil displacement areas of about 30-60 cm2. Using Sigma 70 tensiometer, surface tension and critical micelle concentration (CMC) were determined with the help of the Department of Physico - Chemistry, faculty of Chemistry, Ha Noi University of Science. Among II tested strains, five were able to decrease the surfacetention to levels below 25 mN/m when cultivated in molasses medium. Before growth, surfacetension of molasses medium is about 48.064 mN/m (because the control medium itself reducedthe surface tension to some extent). After growth in this medium, DB7 strain could reduce the tension from 49.03 mN/m to 24.494 mN/m. There fore, surface tension reduction of the DB7strain is 49 %. For CMC study, a range of cultivated medium dilution from 1.5 - 27% (v/v) wasprepared. Surface tension measurement of each was done. Results showed that T, strain hadCMC as 2- 3% (v/v). T1 is a rod shaped spore - forming, gram positive, catalaza potisive, motile, facult ativeanaerobic bacterium. This strain hydrolyzed gelatin, casein and starch, grew in medium with 7%(wt/v) NaCl, at temperature from 25 - 50°C .The T, strain was identified as member of the genusBacillus with high similarity to B.licheniformis.