Morphological studies on the polysaccharide extracted from biofilm produced by Burkholderia multivorans strain C1576

The polysaccharide extracted from the biofilm produced by Burkholderia multivorans C1576 (Epol C1576) contains Rha residues with 25% O-methyl substitution, thus rendering the polymer backbone less polar than other polysaccharides. We already demontrated that Rha makes the polysaccharide able to interact with hydrophobic molecules as well as to exhibit self-aggregation tendency. These two properties might have a particular relevance for the biofilm forming process and for the matrix maintenance. To better disclose the role of Epol C1576 in biofilm matrix formation, morphological investigations were carried out by means of Atomic Force Microscopy (AFM), both in solid and liquid state, as well as by Trasmission Electron Microscopy (TEM). AFM experiments both in solid and liquid state showed that Epol C1576 forms compact structures with globular morphology. The average diameter of the globules, obtained spray-drying polysaccharide solutions on freshly cleaved mica surfaces, was 16 nm. In liquid experiments the diameter was larger, obviously due to hydration of the polymer. The Epol C1576 ability to self-aggregate was demonstrated both in solid and in liquid experiments. TEM experiments gave independent confirmation of both the presence of a globular morphology of the polysaccharidic chain and the ability to self-aggregate, thus excluding artifacts in AFM sample preparation. Parallel to these studies, the molecular dynamic simulation carried out in vacuum on a segment of 100 monosaccharides showed that after 270 ns the polymer chain passes from the starting extended chain to a coiled conformation. In conclusion, the ability of Epol C1576 to assume a compact conformation and to self-aggregate was demonstrated. These properties can be traced back to the presence of Rha residues and their O-methylation.