The highly crystalline PET found in plastic water bottles does not support the growth of the PETase-producing bacterium Ideonella sakaiensis

Abstract

Ideonella sakaiensis produces an enzyme, PETase, that is capable of hydrolyzing polyethylene terephthalate (PET) plastic. We demonstrate that although I. sakaiensis can grow on amorphous plastic, it does not grow on highly crystalline plastic under otherwise identical conditions. Both amorphous film and amorphous plastic obtained from commercial food containers support the growth of the bacteria, whereas highly crystalline film and the highly crystalline body of a plastic water bottle do not support growth. Highly crystalline PET can be melted and rapidly cooled to make amorphous plastic which then supports bacterial growth, whereas the same plastic can be melted and slowly cooled to make crystalline plastic which does not support growth. We further subject a plastic water bottle to a top-to-bottom analysis, finding that only amorphous sections are degraded, namely the finish (threading), the topmost portion of the shoulder which connects to the finish, and the area immediately surrounding the centre of the base. Finally, we use these results to estimate that the percentage of non-degradable plastic in plastic water bottles ranges from 52% to 82% (depending on size), demonstrating that most of the plastic found in PET water bottles will not be degraded by I. sakaiensis.