Effects Of Rhamnolipid On Pseudomonas Aeruginosa ATCC9027Surface Hydrophobicity And Degradation Of Hexadecane By Them

Because biosurfactants can effectively improve biodegradation techn ologyeffects, they are widely applied in managing water, soil and other environments whichare polluted by petroleum hydrocarbons compounds. Resent work in this area suggeststhat there are two mechanisms by which biosurfactants enhance biodegradation ofslightly soluble petroleum hydrocarbons. First, biosurfactants can cause the cellsurface to become more hydrophobic, thereby increasing the association of the cellwith the slightly soluble substrate. Second, biosurfactants can solubilize hydrophobiccompounds within micelle structures, effectively increasing the apparent aqueoussolubility of the organic compounds, and its availability for uptake by a cell. However,little is known about the interaction mechanisms between microbial or petroleumhydrocarbons and biosurfactans. In this study, we further explore the mechanisms thatrhamnolipid biosurfactant alters cell surface hydrophobicity of P. aeruginosa ATCC9027through a series of experiments. Meanwhile, biodegradation of different formshexadecane with rhamnolipid treatment is also examined in order to provide the basisthat rhamnolipid micellar effects can effectively enhance hydrophobic organicpollutants biodegrading.A role of rhamnolipid biosurfactant to enhance the biodegradation ofhydrocarbons is known to be enhancing bacterial cell surface hydrophobicity (CSH)and adhesion of cells to hydrocarbons. Assumptions regarding the mechanism forrhamnolipid to change CSH of Gram-negative bacteria are, rhamnolipid-inducedrelease of lipopolysaccharide (LPS) from cell outer membrane, andadsorption/orientation of rhamnolipid on cell surface. In this study, the relationbetween cell wall LPS or rhamnolipid content and CSH of a Pseudomonas aeruginosabacterium subjected to rhamnolipid treatment was investigated to add insights toconfirm the dominant mechanism. Results showed that the intial CSH of P.aeruginosa ATCC9027grown on hexadecane was determined by the stage of growt,with high initial CSH and high LPS content. After a short-term treatment withdifferent concentrations of rhamnolipid, we found that rhamnolipid sorption decreasedCSH of both exponential-phase and stationary-phase cells. The results indicated thatCSH has a better correlation to the content of rhamnolipid in the cell wall than to thecontent of LPS with the treatment of rhamnolipid, and that adsorption was an important mechanism for rhamnolipid to alter CSH of P. aeruginosa.Then, the effect of rhamnolipid micellar effects on biodegradation of petroleumhydrocarbons is investigated. In this study, handling with different concentrations ofrhamnolipid, we use hexadecane which is complete solubilization state or containingmonomer form as carbon source. When the concentration of rhamnolipid was the same,we found that the biodegradation effect of completely solubilising hexadecane isobviously prior to monomer form presenting. In addition, the influence of5CMCrhamnolipid on biodegradation is better than0.5CMC rhamnolipid whateverhexadecane is form. The results indicated that the solubilization effect for highconcentration of rhamnolipid is more obvious. Due to apparent aqueous solubility ofhexadecane can be significantly enhanced under this concentration, its availability foruptake by a cell will increase.In this study, we deeply reveal the influence mechanism of rhamnolipid on cellsurface hydrophobicity of petroleum hydrocarbons degrading bacteria and theeffective improvement in biodegradation of slightly soluble substrate withrhamnolipid. In conclusion, this work is beneficial exploration for rhamnolipidapplication in bioremediation technology, and it has very important practical value forthe in situ remediation of water, soil environment which have been polluted bypetroleum hydrocarbons compounds at present.