Scientists at the University of Konstanz have identified an enzyme with the capacity to digest particular polyesters and biodegradable plastics while simultaneously breaking down penicillin, raising questions about potential connections to antibiotic resistance mechanisms. The enzyme earned the nickname “Pac-Man enzyme” due to its distinctive molecular structure, which features an exceptionally wide opening at its active site where chemical reactions occur. The discovery emerged from investigations into how microorganisms decompose certain plastic materials and could illuminate whether bacteria are adapting to digest synthetic compounds more rapidly than previously documented.
Biologists Harry Lerner and David Schleheck conducted comprehensive studies of microbial decomposition processes to determine which organisms and biological mechanisms enable plastic breakdown. Their research concentrated on long-chain aliphatic polyesters, a category of biodegradable plastics developed by chemist Stefan Mecking that contain chemical bonds susceptible to microbial degradation. The team analyzed microbial communities and their genetic material to identify genes capable of producing enzymes that dismantle plastic polymers. Their collaborative findings were published in The ISME Journal.
To observe bioplastic behavior in natural conditions, researchers buried samples in forest soil at the university’s botanical garden, positioning them approximately ten centimeters deep in the humus layer where decomposition of cellulose and other natural polymers naturally occurs. Concurrent laboratory experiments used soil from the same location, with powdered bioplastics mixed into samples monitored throughout an entire year. Carbon dioxide measurements tracked microbial metabolic activity as an indicator of decomposition rates.
Results demonstrated substantial differences in degradation patterns. Biodegradable plastic materials were entirely broken down within approximately 250 to 330 days, compared to cellulose which degraded in roughly 80 days, while conventional high-density polyethylene showed virtually no decomposition. These findings underscored the critical importance of polymer chemical composition in determining susceptibility to biological degradation.
Examination of recovered plastic films using electron microscopy revealed numerous microscopic holes matching individual bacterial cell dimensions. This pattern suggested bacteria were penetrating the material rather than merely adhering to surfaces. Researchers hypothesized that bacteria possess plastic-degrading enzymes anchored directly to their cell surfaces, enabling them to digest material while remaining embedded within it—a mechanism potentially explaining the observed microscopic cavities and suggesting that meaningful reductions in plastic pollution would require increased production of biodegradable materials containing bonds microorganisms can break apart.
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