Biopolymer excreted by Pseudoalteromonas antarctica NF3, as a coating and protective agent of liposomes against dodecyl maltoside

The ability of an exopolymer of glycoproteic character (GP) excreted by a n ew gram-negative species Pseudoalteromonas antarctica NF3, to coat phosphat idylcholine (PC) liposomes and to protect these bilayers against the action of the nonionic surfactant dodecyl maltoside was investigated. Transmissio n electron microscopy (TEM) micrographs of freeze fractured liposome/GP agg regates reveal that the addition of the glycoprotetn to liposomes led to th e formation of a film (polymer adsorbed onto the bilayers) that tightly coa ted PC bilayers. The complete coating was already achieved at a PC : GP wei ght ratio of about 9:1. Image analysis profiles of digitalized digitalized TEM micrographs (PC : GP weight ratio 8:2) show that this film was formed b y a multilayer structure. The periods of the average distance of the patter n ordering in layer structures (9-10 layers) were of about 2-3 nm and the t hickness of the complete film was of about 25 nm. Higher amounts of glycopr otein resulted in a growth of this film I-which exhibited at the highest pr oportion of this compound (50% in weight) a multifilm structure. An increas ing resistance of liposomes to be affected by dodecyl maltoside both at sub solubilizing and solubilizing levels occurred as the proportion of the glyc oprotein in the system rose, although this protective effect was more effec tive at low proportions of this compound (PC : GP weight ratios from 9:1 to 8:2), Thus, although a direct dependence was found between the growth of t he enveloping structure and the resistance of the coated liposomes to be af fected by the surfactant, the more effective protection occur red when this structure was a thin film formed by the assembly of various layers of GP o f about 2-3 nm. (C) 1999 John Wiley & Sons, Inc.