Comparative biodeterioration at air interfaces of adipate-based polyester polyurethane coatings by fungal microcolonies of Aureobasidium sp. W12

Abstract

Understanding conditions that enable environmentally common microbes to aggressively deteriorate polymer materials are important for predicting and controlling the environmental fates of these materials. For protective paints and coatings in terrestrial environments, processes at air interfaces are among important factors to understand. Here, we track fungal biodeterioration at air/solid polymer interfaces under nutrient limitation and high humidity, using polymer compositions common in commercial polyester polyurethanes. A fungal isolate, Aureobasidium sp. W12, was collected from an aircraft and identified as a polyester degrader through screening assays. Two polyadipate-based materials were then used for W12 coating deterioration analysis: a commercial polyester polyurethane, Irogran® PS455–203, and a model polyester urethane, PEA-HM. Single and micro-aggregated cell clusters distributed within ∼1.5 mm diameter regions were prepared on the polymer surfaces and incubated with no supplemental nutrients at >95% relative humidity for up to 13 days. Coating deterioration was semi-quantitatively monitored through ester carbonyl loss by transmission FTIR spectroscopy and both materials were rapidly deteriorated, although at different rates. With ∼0.5 monolayer cell surface coverage, PEA-HM showed about 6 × greater molar ester deterioration versus Irogran® over the first 24 h. By 13 days, the polyester fractions of Irogran coatings were deteriorated to an average depth of about 0.1 µm, while PEA-HM coatings about 1 µm thick were completely deteriorated in 5 days within and beyond cell covered regions. Localized analysis of non-uniform PEA-HM deterioration showed that quantities on the order of 10 individual Aureobasidium yeast cells could locally deteriorate through 1–2 µm of PEA-HM coating within 12 days (with deterioration rates up to about 2 × 10−6 µmol ester / (cell × day)). These results correlate conditions and polymer properties that promote high deterioration potentials of Aureobasidium W12 microcolonies at air / coating interfaces.