An estimated 311 million tons of plastics are produced annually worldwide; 90% of these are derived from petrol and the majority of these plastics are used for packaging (water bottles). However, only ~14% of them are collected for recycling.
PET or polyethylene terephthalate is the plastic found in most disposable water bottles and also in polyester clothing, frozen dinner trays and packaging materials.
“If you walk down the aisle in Wal-Mart you’re seeing a lot of PET,” says Tracy Mincer, a scientist from the Woods Hole Oceanographic Institution in Massachusetts.
Biodegradation is known as the chemical dissolution of materials back into natural elements by microorganisms. Why is it important, you may ask? Simply put, the more biodegradable a material is the more environmentally friendly it is.
Plastics are amongst some of the most extensively used materials in most industries, especially in the food packaging industry. However, despite the availability of certain types of biodegradable plastics, the average rate of biodegradation for a common plastic bottle is approximately 100 years.
One such commonly used plastic is polyethylene terephthalate, or PET. Commonly found in water bottles, PET has charmed the manufacturing industry due to its lightweight, colourless and strong nature. But, it is extremely resistant to biodegradation.
However, recent research by a team of Japanese scientists suggests that there exists atleast one species of bacteria that can eat this commonly used plastic. While some previous studies have found several species of fungi capable of growing on PET, no reports existed regarding microorganisms capable of eating it. The research team from Kyoto Institute of Technology and Keio University published their findings in the leading journal Science in 2016.
The study comprised of testing a large amount of sediment, soil and wastewater PET-contaminated samples obtained from a recycling site, following which they were screened for microbial growth. They specifically searched for microbes capable of growing from eating PET, and initially found a consortium of bugs that was capable of breaking down a PET film. The team eventually determined, that only one of the bacterial species, which they later named Ideonella sakainesis, was capable of PET degradation.
Further investigations revealed the Ideonella sakainesis bacterium to function by utilizing two enzymes to break down the PET. While the first enzyme is secreted by the bacterium on adhesion to the PET surface, the secondary enzyme breaks down an intermediate chemical generated by the former enzyme, inside the cell. They work in tandem to provide the bacteria with carbon and energy, both necessary for growth. Using this mechanism for growth, the team reported that a thin PET, when kept at a constant temperature of 30°C could be easily broken down by a community of Ideonella sakainesis.
These findings may provide some insight into methods for managing the > 50 million tons of this particular plastic produced every year. Mincer further commented on the significance of this research on identifying other microbes with similar PET-degrading capabilities.
“Now that we know what we are looking for, we may see these microbes in many areas around the world”, comments Mincer.
Original publication: Yoshida et al.
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