PET is one of the most widely used plastics in the world — more than 50 million tons of PET plastic products are produced worldwide annually. The synthetic polyester polymer is found in disposable plastic drinking bottles as well as polyester clothing, food packaging trays, and blister packs. The plastic material is clear, strong yet flexible, and cheap to produce, making it attractive to manufacturers. The problem with PET is that it doesn’t degrade naturally, so it must be recycled — more than 1.5 billion pounds of PET items were recycled in 2010 in the US. and Canada. It also is highly resistant to bio-degradation by microbes, with only one other species of fungi shown to be capable of breaking down the material.
Not surprisingly, the Ideonella sakaiensis bacterial community was isolated from environmental samples collected from a plastic bottle recycling site. The team collected 250 samples of sediment, soil, and wastewater from the site and discovered a community of organisms capable of breaking down PET. Further analysis revealed that only one species, later named Ideonella sakaiensis, was responsible for this bio-degradation. The researchers isolated the strain and used it in further bio-degradation studies.
The results of these experiments showed that the bacteria used a two-enzyme system to biodegrade the plastic. After adhering to the PET, the bacteria secreted an enzyme that released a chemical from the PET material. This intermediate compound then was imported into the bacterial cell where it was broken down internally by another enzyme. This two-step process provided the bacteria with both carbon and energy to grow, while simultaneously degrading the plastic. According to laboratory tests, Ideonella sakaiensis can break down a thin film of PET slowly over the course of six weeks.
While exciting from a scientific standpoint, Ideonella sakaiensis may not be the cure-all for the plastic bottle problem. Recycling remains the fastest, easiest and cheapest way to remove this form of plastic from the waste stream. Researchers hope these results provide them with the information and tools they need to find other organisms capable of degrading plastic. “This process could be quite common,” said Tracy Mincer of the Woods Hole Oceanographic Institution. “Now that we know what we are looking for, we may see these microbes in many areas around the world.”
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