SCREENING OF RHAMNOLIPIDS FROM Pseudomonas spp. AND EVALUATION OF ITS ANTIMICROBIAL AND ANTIOXIDANT POTENTIAL

Abstract

Biosurfactants are amphipathic compounds that are useful in industries and are also used in bioremediation. Rhamnolipids (RL) are biosurfactant mostly produced by the genus Pseudomonas. This study screened 6 strains of Pseudomonas isolated from underwater cave sediments to determine if they were capable of producing rhamnolipids. The biosurfactant production of potential strains was screened by Parafilm-M Test, Oil spreading technique, Microplate assay, Emulsification Index, CTAB Agar plate method, Anthrone test, and Thin Layered Chromatography. The study showed that only 3 strains had the potential to produce rhamnolipids, these were Pseudomonas poae, Pseudomonas fluorescens and Pseudomonas libanensis. The antimicrobial activity of the crude rhamnolipid extracts was tested against two Gram-negative bacteria (Escherichia coli, Serratia marcescens) and two Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus) by the conventional minimum  inhibitory concentration (MIC). The antioxidant activity of the crude rhamnolipid extracts was determined through DPPH free radical scavenging assay. All rhamnolipid extracts had a positive correlation between increasing concentrations and the zone of inhibition against test microorganisms. Rhamnolipids from P. libanensis had the lowest MIC among the other extracts, indicating its potency against the test bacteria. The rhamnolipid extracts were effective at inhibiting the test bacteria compared to the positive control, Nitrofurantoin. The antioxidant activity of the crude rhamnolipid extracts was determined through DPPH. Crude rhamnolipid extracts exhibited antioxidant activity but not as great as that of ascorbic acid.