ABSTRACT The use of biosurfactants produced from bacteria is an alternative approach to bioremediate the sites contaminated by crude oil which often contains heavy metals. However, there are limited studies on the production of biosurfactants in the presence of both hydrocarbons and heavy metals. Hence, this study aims to investigate the effect of cadmium (Cd) on biosurfactant production by Exiguobacterium profundum, previously isolated from a hydrocarbon refinery and characterised. E. profundum was able to grow in culture media containing crude oil as the sole carbon source and in the presence of 0.1 mg/L Cd, demonstrating its resistance to Cd. The harvested bacterial cells showed 58.4% cell adherence to crude oil using bacterial adhesion to hydrocarbons (BATH) assay, suggesting hydrophobic cell surfaces due to potential secretion of biosurfactants. In the presence of 0.1 mg/L Cd, biosurfactant dry mass was significantly increased (p<0.05) by 29.6% when compared to the control without Cd. At room temperature, the biosurfactant was able to form emulsion layers with all three tested hydrocarbons, with the calculated emulsification index of 35.8 ± 1.43% in benzene (p<0.05) followed by 5.0 ± 0.0% in hexane and 8.3 ± 3.36% in crude oil. The biosurfactants tested positive for the presence of sugar moiety but negative for protein. This suggested that the biosurfactants produced by E. profundum are from the glycolipid family. The presence of Cd significantly increased the secretion of biosurfactants suggesting that E. profundum employed the biosynthesis and secretion of glycolipid biosurfactants as mechanisms to counter the toxicity due to Cd.
View Full Article
|