Promising biotechnological applications of antibiofilm exopolysaccharides

Polysaccharides are polymers of carbohydrates with an enormous structural diversity, from long linear repetition of the same monomer to highly branched structures of different sugars. This high structural diversity reflects the functional diversity of these molecules. There are two types of polysaccharides, storage polysaccharides (i.e. glycogen) and structural polysaccharides, which are normally secreted by the cell and form different cell structures (i.e. cellulose, chitin). Extracellular polysaccharides or exopolysaccharides belong to this last group. Exopolysaccharides are produced not only by microorganisms, but also by algae, plants and animals (Sutherland, 2005). Bacterial exopolysaccharides are a major component of the extracellular polymeric substance (EPS) or matrix of biofilms, and mediate most of the cell-to-cell and cell-to-surface interactions required for biofilm formation and stabilization (Flemming and Wingender, 2010). The matrices of biofilms from natural environments, such as marine and fresh water, soil, or chronic infections, contain a ubiquitous composition of polysaccharides. More than 30 different matrix polysaccharides have been characterized so far. Several are homopolysaccharides (i.e. glucans, fructans, cellulose), but most of these are heteropolysaccharides consisting on a mixture of sugar residues. Exopolysaccharides can even differ between strains of single species, as exemplified by strains of Pseudomonas aeruginosa, which can produce one, two or three different exopolysaccharides (alginate, Pel and Psl) (Ryder et al., 2007). Since most mutants deficient in the synthesis of exopolysaccharides are impaired for biofilm formation it was assumed that bacterial exopolysaccharides play only a structural role in biofilms (Sutherland, 2001). However, in recent years an unexpected function for these molecules as inhibitors of biofilm formation has been described. This new function has been thoroughly reviewed by Rendueles and colleagues in a recent issue of Environmental Microbiology (2012). Polysaccharides with the ability to inhibit and/or destabilize biofilm formation are referred to as antibiofilm polysaccharides, and their production appears to be a well-conserved ability among living organisms. Interestingly, antibiofilm polysaccharides do not have biocidal activity, a property that could increase the technological applications of these molecules as antibiofilm agents in industry and medicine by diminishing the emergence of resistance by natural selection.