Assembly properties and applications of a new exopolymeric compound excreted by Pseudoalteromonas antarctica NF<inf>3</inf>

The self assembly properties and applications of an exopolymeric compound (EC) of a glycoprotein character excreted by a new Gram-negative species, Pseudoalteromonas antarctica NF3, have been reviewed. This compound exhibited surface-active properties in water, with a concentration of 0.20 mg ml-1 being the key value associated with its physicochemical properties. Unsonicated EC aqueous dispersions showed the coexistence of concentric multilamellar and small unilamellar aggregates by transmission electron microscopy (TEM). Sonication of these dispersions revealed that each lamellae of the initial multilamellar structures were made up of various subunits coiled coils. As for the ability of this exopolymeric biomaterial to coat phosphatidylcholine (PC) liposomes and to protect these vesicles against different surfactants, freeze-fracture TEM micrographs of liposome/EC aggregates revealed that the addition of the EC to liposomes led to the formation of a film (polymer adsorbed onto the bilayers) that coated very well the PC bilayers. The complete coating was already achieved at a PC: EC weight ratio of about 9:1. An increasing resistance of PC liposomes to surfactants (in particular sodium dodecyl sulfate) occurred as the proportion of EC in the system rose, although this effect was more effective at low EC proportions (PC: EC weight ratios from 9:1 to 8:2). Although a direct dependence was found between the growth of the enveloping structure and the resistance of the coated liposomes to be affected by the surfactants, the best protection occurred when this structure was a thin film of about 20-25 nm formed by nine to ten layers of about 2-3 nm.