Fungal communities associated with degradation of polyester polyurethane in soil

Abstract

Soil fungal communities involved in the biodegradation of polyester polyurethane (PU) were investigated. PU coupons were buried in two sandy loam soils with different levels of organic carbon: one was acidic (pH 5.5), and the other was more neutral (pH 6.7). After 5 months of burial, the fungal communities on the surface of the PU were compared with the native soil communities using culture-based and molecular techniques. Putative PU-degrading fungi were common in both soils, as <45% of the fungal colonies cleared the colloidal PU dispersion Impranil on solid medium. Denaturing gradient gel electrophoresis showed that fungal communities on the PU were less diverse than in the soil, and only a few species in the PU communities were detectable in the soil, indicating that only a small subset of the soil fungal communities colonized the PU. Soil type influenced the composition of the PU fungal communities. Geomyces pannorum and a Phoma sp. were the dominant species recovered by culturing from the PU buried in the acidic and neutral soils, respectively. Both fungi degraded Impranil and represented >80% of cultivable colonies from each plastic. However, PU was highly susceptible to degradation in both soils, losing up to 95% of its tensile strength. Therefore, different fungi are associated with PU degradation in different soils but the physical process is independent of soil type.

FIG. 1.

Comparison of DGGE profiles of soil fungal communities and fungal communities growing on the surface of PU buried in both soil types.

FIG. 2.

Phylogenetic analysis of isolates recovered from the surface of buried PU (boldface). ITS1-5.8S-ITS2 sequences from the isolates were compared to putatively closely related species using a maximum parsimony phylogenetic tree (bootstrap corrected with 1,000 samples). The tree is rooted using the outlying fungi Boletus satanas, Russula compacta, Leucostoma persoonii, Aspergillus fumigatus, Candida albicans, and Kluyveromyces lactis.

FIG. 3.

Comparison of DGGE bands produced by fungi isolated in pure culture from buried PU with bands produced by fungal communities growing on PU buried in neutral and acidic soils. DGGE bands of the isolates indicated by lined arrows migrate to the same position as bands within the DGGE profiles of fungal communities from PU. Numbered bands were cloned into E. coli, sequenced, and identified.