Widespread PET-degrading enzymes discovered in the world’s oceans
Researchers at King Abdullah University of Science and Technology (KAUST) report that enzymes capable of breaking down polyethylene terephthalate (PET) are already common in the ocean. The team analyzed 415 ocean samples and found a PET-degrading signature — an "M5" motif linked to functional PETase enzymes — in nearly 80% of them.
What the M5 motif means
The M5 motif acts like a molecular fingerprint that indicates an enzyme is likely able to attack PET plastic. According to study co-leader Carlos Duarte, the motif helps researchers identify which enzyme variants are functional and reveals how PETases may have evolved from older hydrocarbon-degrading enzymes.
"The M5 motif acts like a fingerprint that tells us when a PETase is likely to be functional, able to break down PET plastic," Duarte explained. "Its discovery helps us understand how these enzymes evolved from other hydrocarbon-degrading enzymes."
Scientists suggest that in parts of the ocean where organic carbon is scarce, microbes have adapted existing enzymatic machinery to make use of a new, human-made carbon source: plastic. This adaptation may be an evolutionary response to the steady accumulation of plastic waste in the environment since mass production began in the 1950s.
Why this matters
Until about 2016, many researchers believed PET could not be broken down biologically. The new finding — that PETase-like enzymes are widespread — expands hope that natural or engineered enzymes can play a role in degrading plastic waste, aiding cleanup efforts and improving recycling or treatment processes.
However, the authors and other experts caution against seeing enzymes as a simple fix. While PETases provide promising models for optimization in the lab and deployment in treatment facilities, reducing plastic production, improving waste management, and preventing pollution at the source remain essential.
Human health and environmental context
Plastic pollution affects marine ecosystems and human health: microplastics have been detected in water, food, blood and even brain tissue, and have been associated with increased risks such as cardiovascular and respiratory problems. Relying on biodegradation alone would not address these widespread impacts or the continued flow of new plastic into the environment.
Next steps
Researchers will likely use the diverse natural PETase variants identified in this study as templates for laboratory optimization — improving activity, stability and suitability for industrial use. At the same time, monitoring, better disposal practices and policies to curb plastic production remain vital.
Study details: 415 ocean samples were screened for PETase-associated sequences; the M5 motif appeared in nearly 80% of samples, indicating widespread presence of PET-degrading potential in marine microbes.
