Plasticizers increase adhesion of the deteriogenic fungus Aureobasidium pullulans to polyvinyl chloride

Initial adhesion of fungi to plasticized polyvinyl chloride (pPVC) may dete rmine subsequent colonization and biodeterioration processes. The deterioge nic fungus Aureobasidium pullulans was used to investigate the physicochemi cal nature of adhesion to both unplasticized PVC (uPVC) and pPVC containing the plasticizers dioctyl phthalate (DOP) and dioctyl adipate (DOA). A quan titative adhesion assay using image analysis identified fundamental differe nces in the mechanism of adhesion of A. pullulans blastospores to these sub strata, Adhesion to pPVC was greater than that to uPVC by a maximum of 280% after a 4-h incubation with 10(8) blastospores ml(-1). That plasticizers e nhance adhesion to PVC was confirmed by incorporating a dispersion of both DOA and DOP into the blastospore suspension. Adhesion to uPVC was increased by up to 308% in the presence of the dispersed plasticizers. Hydrophobic i nteractions were found to dominate adhesion to uPVC because (i) a strong po sitive correlation was observed between substratum hydrophobicity (measured by using a dynamic contact angle analyzer) and adhesion to a range of unpl asticized polymers including uPVC, and (ii) neither the pH nor the electrol yte concentration of the suspension buffer, both of which influence electro static interactions, affected adhesion to uPVC. In contrast, adhesion to pP VC is principally controlled by electrostatic interactions. Enhanced adhesi on to pPVC occurred despite a relative reduction of 13 degrees in the water contact angle of pPVC compared to that of uPVC. Furthermore, adhesion to p PVC was strongly dependent on both the pH and electrolyte concentration of the suspension medium, reaching maximum levels at pH 8 and with an electrol yte concentration of 10 mM NaCl. Plasticization with DOP and DOA therefore increases adhesion of A. pullulans blastospores to pPVC through an interact ion mediated by electrostatic forces.