The Influence Mechanism Research Of Rhamnolipid On Surface Hydrophobicity Of Petroleum Hydrocarbons Degrading Bacteria

One possible way for rhamnolipid-biosurfactant to enhance the biodegradation ofpetroleum hydrocarbons is to alter bacterial cell surface hydrophobiciy （CSH）. In orderto know better this role of biosurfactant, the effect of rhamnolipid on CSH ofPseudomonas aeruginosa ATCC9027grown on glucose or glycerol, with respect tosurface chemicals and the adsorbed rhamnolipid, was investigated in this study.In this study, an orthogonal designing method was used for the optimal design of thefermenatation conditions for P. aeruginosa ATCC9027to produce rhamnolipid. Theoptimal condition, for the most production of rhamnolipid, was37℃with the optimalmedium composed of15g/l glucose,10g/l peptone,0.4g/l MgSO₄,1.07g/l NH₄Cl,1.49g/l KCl and18.9g/l Tris-HCl. The rhamnolipid produced under the optimal conditionswas characterized, and the results showed that P. aeruginosa ATCC9027producedmonorhamnolipid only. The average molecular weigh and the critical micelleconcentration of the rhamnolipid mixture was507g/mol and42.1mg/l or83μMrespectively.The change of CSH and outer membrane chemical compositions of P. aeruginosaunder different carbon sources was either investigated. It was found that the CSH of P.aeruginosa varied along with the growth. The CSH of P. aeruginosa strated to increasesince early exponential phase, reached the maximum value at middle exponential phaseand then decreased and kept stable at stationary phase. What’s more, the CSH of P.aeruginosa was related to the carbon source. For cells grown on more hydrophobiccarbon source, the CSH was higher. There was a negative correlation betweenlipopolysaccharide （LPS） content in outer membrane and CSH, and no obvious relationsbetween porin content and CSH.The data-mixed diagram showed that the change of P. aeruginosa CSH underrhamnolipid was very likely due to a mixed effect of LPS content change andrhamnolipid adsorption. During the incubation of cells in the presence of rhamnolipid,the exponential-phase cells grown on glucose or glycerol both adsorbed rhamnolipidstrongly, which accounted more for the rapid CSH decrease in the first10minutes of theincubation. For the stationary-phase cells, however, the rhamnolipid adsorption wasmuch slower. The modest increase of CSH at the very beginning of incubation was morelikely due to the LPS content reduction.