Researchers have discovered new strains of Pseudomonas bacteria that feed on the PET plastic used in drink bottles, and turn it into a more valuable, biodegradable form of plastic. The discovery suggests a way to keep billions of pounds of discarded plastic out of landfills; a 2006 study [pdf] found that less than 25 percent of PET plastic is currently recycled because the industry doesn’t have enough use for the end product.
Getting high-quality material — such as plastics suitable for packaging food or beverages —- back out of recycled plastic is more expensive than making virgin PET, so most plastic bottles are recycled into lower-grade, and less valuable, plastic. But there’s only so much demand for lower-grade plastics, says microbiologist and coauthor Kevin O’ Connor…. “The problem is that the market [for recycled PET] is saturated” [Science News].
The researchers knew that heating PET plastic in the absence of oxygen produces a substance called terephthalic acid, which some bacteria feed on. They also know that other bacteria produce a high quality plastic called PHA that could have numerous applications in medicine–because PHA plastic is biodegradable, it’s ideally suited for sutures, wound dressings, and various implants. The researchers hoped to find a bacteria that fed on terephthalic acid and produced PHA plastic, so they collected soil bacteria from a bottle processing plant.
As reported in their paper, published in Environmental Science and Technology [subscription required], after 48 hours they screened each culture for PHA. Three cultures, all similar to known strains of Pseudomonas, accumulated detectable quantities of the valuable plastic. The next step is to improve the efficiency of the process, says O’Connor. “A quarter to a third of each cell is filled with plastic – we want to increase that to 50 to 60%” [New Scientist].