DETERMINATION OF OPTIMUM CONDITIONS AND STABILITY STUDY OF BIOSURFACTANT PRODUCED BY Bacillus subtilis UKMP-4M5 (Penentuan Keadaan Optimum dan Kajian Kestabilan Biosurfaktan yang Dihasilkan oleh Bacillus subtilis UKMP-4M5)

Bacillus subtilis UKMP-4M5 was isolated from a hydrocarbon contaminated site which was found to be the most potential biosurfactant producer. Isolates were grown in a mineral salt medium (MSM) supplemented with sunflower oil (1% v/v) as the main carbon source. Screening was based on both qualitative (oil spreading technique) and quantitative (emulsification index and surface tension measurement) methods. B. subtilis UKMP-4M5 produced the highest oil displacement activity with and emulsification index of 17%. It also reduced surface tension of culture medium from 58.95 to 41.75 mN/m. B. subtilis UKMP- 4M5 produced biosurfactant with surface tension measurement of 32.7 ± 0.66 mN/m using 2% (v/v) palm oil and 0.5% (w/v) yeast extract as carbon and nitrogen sources respectively. The tested biosurfactant exhibited excellent thermal (up to 120 °C) and pH (6.0 - 8.0) stability as well as high tolerance for varying salt concentrations (1 - 5% w/v) in terms of surface tension reducing ability. This suggests potential applications in fields such as enhanced oil recovery, bioremediation, and the food industry.