Project Summary/Abstract This project will combine molecular dynamics simulations and other types of molecular mechanics calculations with various experimental methods to characterize the biofilms formed by opportunistic pathogen species belonging to the Burkholderia cepacia Complex (BCC) and by Klebsiella pneumoniae. Bacterial biofilms constitute a serious concern in infections since they confer increased resistance towards antimicrobial therapies. In biofilms, bacteria live within a hydrated matrix composed of various macromolecules, and in particular polysaccharides, which are primarily responsible for its formation. Understanding the details of biofilm matrix structure can be of significant utility in designing novel strategies for treating infections. This is the main objective of this proposal, which is a request for the continuation of a currently funded NIH study (GM123283) based on the results acquired in this current project characterizing the structure of polysaccharides produced by species of the BCC and K. pneumoniae. These polymers contain clusters of non-polar rhamnose residues that confer a less polar character to the chains, suggesting the possible formation of hydrophobic juncture zones in the gel- like structures of their biofilm matrices, and possibly constituting targets for biofilm disruption. On the basis of the results already achieved, the following research lines will be explored both experimentally and by computer modelling: 1) Structurally different rhamnose-rich polysaccharides produced by Burkholderia and Klebsiella will be studied to investigate their morphology and aggregation tendency, with the objective of modeling their biofilm matrix architectures. 2) The interactions of matrix polysaccharides with molecules participating in quorum sensing systems will be studied to define the role of the matrix in cell-cell communication. 3) The possibility of weakening matrix architecture by using specific agents will be explored using three systems, all designed to target matrix junction zones: i) oligosaccharides containing rhamnose residues; ii) specific peptides which have already been found, by means of phage display procedures, to bind bacterial polysaccharides; iii) synthetic glycopeptides obtained binding rhamnose residues to selected peptides investigated in point ii). Changes in biofilm matrix morphologies will be studied by adding these test molecules to bacterial cultures.

Project Narrative Biofilms produced by bacteria are a significant and serious problem in many types of infections, and contribute to bacterial antibiotic resistance. Biofilms are made up of various macromolecules, but polysaccharides are the main component responsible for their structure. This project will exploit interesting results obtained by our groups on the structure-function relationships of bacterial extracellular polysaccharides to gain further information on the possibility of disrupting biofilms, without the use of antibiotics, by employing a coordinated combination of experiments and computer simulations to characterize the biofilm polysaccharides produced by different bacteria of medical concern (species of the Burkholderia cepacia Complex and of Klebsiella), their contribution to the overall stability of biofilms, their interactions with quorum sensing molecules, and possible biofilm disrupting agents which could be used for biofilm prevention and control.