Bacteria are everywhere, silently going about their business of breaking down cellulose, fermenting foods or fixing nitrogen in the soil, among a host of other activities.

Given their ubiquity and diversity of functions, biotechnologists have been searching for new uses for different strains of the microscopic organisms, such as consuming oil spills or even capturing images. Now biologists at the University College Dublin in Ireland have found that a strain of Pseudomonas putida can exist quite happily on a diet of pure styrene oil–the oil remnant of superheated Styrofoam–and, in the process, turn the environmental problem into a useful, biodegradable plastic.

Kevin O’Connor and his European colleagues turned the polystyrene into an oil through pyrolysis–a process that heats the petroleum-based plastic to 520 degrees Celsius in the absence of oxygen. This results in a chemical cocktail made up of more than 80 percent styrene oil plus low volumes of other toxicants. The researchers then fed this brew to P. putida CA-3, a special strain of a common soil microbe, fully expecting that the oil would have to be further purified in order to enable bacterial growth.

But the bacteria thrived on this new diet, turning 64 grams of undistilled styrene oil into nearly 3 grams of additional bacteria. In the process, the bacteria stored 1.6 grams of the energy of the styrene oil as a biodegradable plastic called polyhydroxyalkanoates, or PHA. This plastic can stand up to heat but also breaks down more naturally in the environment than petroleum-based products. Thus, though the biology-powered process results in some toxic byproducts such as toluene and requires significant energy to drive the pyrolysis, it fuels hopes that Styrofoam–and the polystyrene molecule that makes it–can become more environmentally friendly.

This would be good news for the U.S., which produced three million tons of polystyrene in 2000, according to the EPA, and threw away 2.3 million tons of the stuff, consigning the waste to rest for long years in landfills. The PHA from this process could be turned to more productive uses; it is already being used to make everything from forks to vitamins. And the process might not just be useful for getting rid of disposable cups. "Due to the general applicability of pyrolysis for plastic conversion to an oil and the large number of microorganisms capable of PHA accumulation from a vast array of molecules, the principle of the process described here can be applied for the recycling of any petrochemical plastic waste," the scientists claim in the paper presenting their findings in the April 1 issue of Environmental Science & Technology. Apparently, bacteria recycle, too.

By David Biello

Scientific American