Biodegradation of poly(vinyl alcohol) in selected mixed microbial culture and relevant culture filtrate

Abstract

The dependence of PVA biodegradation on polymer molecular weight, degree of hydrolysis, and content of head-to-head structural units was investigated in the presence of a PVA-degrading microbial population and of the relevant culture supernatant. Respirometric tests carried out in the presence of the selected microbial population evidenced a limited but significant delay in the mineralization profile depending upon the degree of PVA hydrolysis, whereas no remarkable effect by molecular weight was detected. Five bacterial strains were isolated from the PVA-degrading microbial population, but only the degradation of low molecular weight fractions was recorded in cultures inoculated with single bacterial strains. The exclusive attack of low molecular weight fractions is in accordance with the occurrence of an additional degradation mechanism different from that generally proposed for PVA biodegradation. Experiments carried out in the presence of the culture supernatant clearly demonstrated the presence of a PVA degrading enzymatic system in the solution. Kinetic studies carried out under the reported conditions suggested the occurrence of a random cleavage of PVA chains. No influence of both molecular weight and content of head-to-head structural units on the enzymatic degradation process was observed. Enzymatic assays excluded the presence of extracellular esterases in the culture supernatant but confirmed the presence of oxidases.