Effect of a Pseudomonas rhamnolipid biosurfactant on cell hydrophobicity and biodegradation of octadecane

Abstract

In this study, the effect of a purified rhamnolipid biosurfactant on the hydrophobicity of octadecane-degrading cells was investigated to determine whether differences in rates of octadecane biodegradation resulting from the addition of rhamnolipid to four strains of Pseudomonas aeruginosa could be related to measured differences in hydrophobicity. Cell hydrophobicity was determined by a modified bacterial adherence to hydrocarbon (BATH) assay. Bacterial adherence to hydrocarbon quantitates the preference of cell surfaces for the aqueous phase or the aqueous-hexadecane interface in a two-phase system of water and hexadecane. On the basis of octadecane biodegradation in the absence of rhamnolipid, the four bacterial strains were divided into two groups: the fast degraders (ATCC 15442 and ATCC 27853), which had high cell hydrophobicities (74 and 55% adherence to hexadecane, respectively), and the slow degraders (ATCC 9027 and NRRL 3198), which had low cell hydrophobicities (27 and 40%, respectively). Although in all cases rhamnolipid increased the aqueous dispersion of octadecane at least 10(4)-fold, at low rhamnolipid concentrations (0.6 mM), biodegradation by all four strains was initially inhibited for at least 100 h relative to controls. At high rhamnolipid concentrations (6 mM), biodegradation by the fast degraders was slightly inhibited relative to controls, but the biodegradation by the slow degraders was enhanced relative to controls. Measurement of cell hydrophobicity showed that rhamnolipids increased the cell hydrophobicity of the slow degraders but had no effect on the cell hydrophobicity of the fast degraders. The rate at which the cells became hydrophobic was found to depend on the rhamnolipid concentration and was directly related to the rate of octadecane biodegradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Rhamnolipid-induced shedding of flagellin fromPseudomonas aeruginosaprovokes hBD-2 and IL-8 response in human keratinocytes

“…Candidate molecules are biosurfactants. P. aeruginosa can produce biosurfactants, among them are rhamnolipids, which have been reported to modulate and shear parts of its cell surface to adapt to certain environmental cues (Zhang and Miller, 1994;Al Tahhan et al, 2000). To characterize this P. aeruginosa-derived shedding factor, it was precipitated upon acidification of the culture filtrates, chemical properties characteristic for rhamnolipids (Rahman et al, 2002).…”

Characterization of bacterial strains able to grow on high molecular mass residues from crude oil processing

“…Cell hydrophobicity was analyzed by a modi¢ed method to monitor bacterial adhesion to hydrocarbons [23]. One ml of cells grown in minimal salts M9 medium with hexadecane as the carbon source was centrifuged and the cells resuspended in 1 ml of minimal salts medium.…”

Structural and Serological Characterisation of the O‐Antigenic Polysaccharide of the Lipopolysaccharide from Acinetobacter Junii Strain 65

“…increase the hydrophobicity) in the molecule, and the occurrence of branched polymers, particularly those that contain two or three sugars in the branching unit [12,15,251. Species of Acinetobacter have been reported as possessing hydrophobic cell surfaces 128, 291, and it has been suggested that a hydrophobic cell surface may be a requirement for the enhanced biodegradation of carbon substrates [30], and the production of surface activity [3 11. Thus, the occurrence of hydrophobic 0-antigens and LPS in Acinetobacter is consistent with the production of surfaceactive molecules [32-341 and growth on hydrophobic substrates [35 -371.…”