Characterization of liposomes formed by lipopolysaccharides from Burkholderia cenocepacia, Burkholderia multivorans and Agrobacterium tumefaciens: from the molecular structure to the aggregate architecture.

The microstructure of liposomes formed by the lipopolysaccharides (LPS) derived from Burkholderia cenocepacia ET-12 type strain LMG 16656, Burkholderia multivorans strain C1576 and Agrobacterium tumefaciens strain TT111 has been investigated by a combined experimental strategy, including dynamic light scattering (DLS), small-angle neutron scattering (SANS) and electron paramagnetic resonance (EPR). The results highlight that the LPS molecular structure determines, through a complex interplay of hydrophobic, steric and electrostatic interactions, the morphology of the aggregates formed in aqueous medium. All the considered LPS form liposomes that in most cases present a multilamellar arrangement. The thickness of the hydrophobic domain of each bilayer and the local ordering of the acyl chains are determined not only by the molecular structure of the LPS glycolipid portion (lipid A), but also, indirectly, by the bulkiness of the saccharidic portion. In the case of a long polysaccharidic chain, such as that of the LPS derived from Burkholderia multivorans, liposomes coexist with elongated micellar aggregates, whose population decreases if a typical phospholipid, such as dioleoyl phosphatidylethanolamine (DOPE) is introduced in the liposome formulation. The effect of temperature has also been considered: for all the considered LPS an extremely smooth transition of the acyl chain self-organization from a gel to a liquid crystalline phase is detected around 30-35 °C. In the biological context, our results suggest that the rich biodiversity of LPS molecular structure could be fundamental to finely tune the structure and functional properties of the outer membrane of Gram negative bacteria