A fungus grows on polyurethane, even without oxygen

Polyester polyurethane is the plastic of foams, seals and coatings, and it is regarded as hard to break down biologically. In 2011 a team from Yale published in Applied and Environmental Microbiology the results of screening several dozen endophytic fungi collected in the Ecuadorian Amazon for the ability to degrade it. Several isolates degraded the polymer efficiently, both in solid medium and in liquid suspension.

The strongest activity was found in the genus Pestalotiopsis, although it was not a feature of the whole genus — isolates of the same species differed. Two isolates of Pestalotiopsis microspora grew on polyurethane as their sole carbon source, and did so under both aerobic and anaerobic conditions. Molecular characterisation pointed to a serine hydrolase as the enzyme responsible.

Anaerobic growth matters more than it first appears. The interior of a landfill is an oxygen-free environment, so an organism that degrades plastic only in the presence of air has little use there. The ability to grow without oxygen moves the result from the category of laboratory curiosity to the category of lead worth following.

Proportion is still needed. This is a culture result, obtained on one type of plastic at constant temperature on a controlled medium — not a working waste technology. The paper shows that endophytes are a promising source of metabolic pathways useful in bioremediation, and that is how it states its conclusion. The road from a flask to an industrial plant is long, and most candidates do not finish it.

It is also worth remembering that polyurethane names a family of plastics rather than one material. The study concerned polyester polyurethane, in which the ester bonds are relatively open to enzymatic hydrolysis. Polyether grades, common in insulation and furniture foam, are considerably more durable in that respect. The result does not transfer automatically to any plastic, and the authors do not suggest that it does.

What the evidence actually shows

The laboratory result concerned one polyester polyurethane, not every material called “plastic.” Endophytes isolated from plant stems in an Ecuadorian forest were screened using an Impranil dispersion. Two isolates identified as Pestalotiopsis microspora, E2712A and E3317B, grew when polyurethane was the sole carbon source and retained degradation activity in an anaerobic chamber. For E2712A, dispersion-clearing rates after one and two weeks were similar with and without oxygen. An extracellular fraction implicated an approximately 21-kDa serine hydrolase. “Eats plastic” is nevertheless shorthand: the experiment used a susceptible polyester PUR in controlled medium and measured loss of turbidity and chemical change, not the disappearance of finished foams, adhesives, or landfill waste. The trait was also isolate-specific—one tested Pestalotiopsis showed no detectable activity—so it should not be generalized to the entire genus.

What does it mean for a plastic to degrade?

A screening experiment needs a rapid signal to select promising isolates for closer examination. Clearing a dispersion can provide that signal, but it does not answer every question about the polymer’s fate. Distinguish a change in appearance, a change in chemical structure, a loss of mass and an organism’s use of the resulting products. Each observation addresses a different part of the process.

The 2011 paper is the starting point for this story. A later study of other fungi, published in 2019, also assessed mass loss in tested polyurethane materials and analysed changes to them. Outcomes depended on the kind of plastic and its structure. This was a separate experiment, not a field trial of the same Amazonian isolates. Reading the studies together shows why multiple measurements matter and why the word “polyurethane” alone cannot predict an outcome.

How to read a proposed application

Imagine a fictional headline: “Fungus removes half the plastic.” Before treating it as a waste solution, ask: half of what, measured how, after how long, and compared with which control? Was the material shredded or pretreated? What remained afterwards? Without those details, the number does not yet describe the performance of a technology.

These are questions for evaluating a report, not a list of results obtained in the papers discussed here. A working process would also need assessment of inputs, reproducibility and breakdown products. A promising isolate might begin a search for an enzyme rather than become an organism intended for release into a landfill. The studies do not establish a method for home composting plastics or justify introducing plastic and fungi into soil. The compelling part of the discovery is a specific biological ability that can be investigated further, using a precisely identified material and a measurable outcome. Keeping those details attached makes the result more useful to readers and to subsequent research.