Engineered compost enzyme degrades 1.4% of a shoe sole in three days

Hold that rate steady and the same piece of sole clears in about 214 days: 100 divided by 1.4, multiplied by the three days of the experiment ^[15]. That is a magnitude check on a linear assumption. The published account does not include a time course or a degradation figure for the unmodified CCPUR1, so neither the shape of the curve nor the size of the gain from the mutations can be read from it ^[18].

The input, though, is unambiguous. The foam went into the reaction as sold, with no chemical or mechanical preparation step. "This is an early demonstration that shows that we can degrade polyurethane with enzymes without processing it beforehand," said Pedro Paiva of the University of Porto, a co-first author on the paper. "It's quite significant." ^{[10] [17]}

Other groups can pick up the design route. CCPUR1 came out of a survey of microorganisms already used around the world to break down garbage, and of the enzymes those organisms use on plastics ^[5]. Simulations showed how the protein sat against plastic-like material, and the team then edited the bacterium's DNA to swap a few key amino acids for bulkier ones ^[6]. "What if we try to change specific amino acids to larger ones that could better fill the empty space between the enzyme and the substrate?" said Paiva ^[7]. The published title describes the result as a thermostable polyurethane hydrolase ^[13].

Polyurethane output runs around 20 million tonnes a year, which the researchers put at more than 5% of all plastics reaching the market ^[2]. By that share the whole market sits below roughly 400 million tonnes a year ^[16]. The thermoset grades turn up in soles and heels ^[3], and the stated target is those products piling up in landfills ^[14]. The case for enzymes here rests on mild conditions. "The real plus about using enzymes for recycling is that they work under mild conditions, so at lower temperatures and pressures than currently used in most recycling technologies today," said Rosie Graham of Aarhus University, the other co-first author ^{[9] [17]}.

What comes off the polymer matters as much as how fast. The team reports the enzyme splitting the waste into smaller, reusable pieces ^[8]. Calling any of this recycling depends on recovering usable feedstock. Graham put the premise plainly: "We have flooded the environment with so much plastic of different kinds," she said. "But there are lots of organisms out there that are already using these materials as a source of energy." ^[11] The researchers describe the work as still in its infancy ^[12].