Cyanobacterium-Derived Extracellular Carbohydrate Polymer for the Controlled Delivery of Functional Proteins

The unicellular cyanobacterium Cyanothece sp. CCY 0110 is a highly efficient producer of extracellular polymeric substances (EPS), releasing up to 75% of the polymer to the culture medium. The carbohydrate polymer released to the medium (RPS) was previously isolated and characterized; it is composed of nine different monosaccharides including two uronic acids, and also containing peptides and sulfate groups. Here it is shown that the RPS spontaneously assembles with proteins at high concentrations leading to a phase transition. The proteins are released progressively and structurally intact near physiological conditions, primarily through the swelling of the polymer-protein matrix. The releasing kinetics of the proteins can be modulated through the addition of divalent cations, such as calcium. Notably, the polymer is not toxic to human dermal neonatal fibroblasts in vitro at RPS concentrations bellow 0.1 mg mL^-1 . The results show that this polymer is a good candidate for the delivery of therapeutic macromolecules.