Scientists bioengineer mussel-inspired microorganisms to enhance PET plastic degradation

Scientists at Rice University, US, have bioengineered microorganisms inspired by the adhesive power of mussels, which can be employed to enhance PET degradation when combined with PETase enzymes. 

The research, published in Small Methods, a nanoscience and nanotechnology journal focusing on methods applicable to nano- and microscale research, showcases the potential of sticky proteins and bacteria to adhere to plastic surfaces more effectively. Efficiently degrading PET poses challenges due to its notorious resistance to decomposition, often taking centuries to break down. 

Mengxi Zhang, first author of the study, tells Packaging Insights: “Each year, the global plastic production surpasses an astonishing 350 million tons, and within the US market, PET products alone constitute a substantial 64% of this total. This vast quantity underscores the urgent imperative for effective PET degradation to facilitate plastic recycling.”

“However, PET is notorious for its low chain mobility and chemical inertness, presenting a formidable challenge for its degradation. Surface display of PET degradation enzymes on bacteria is considered a powerful tool to combat the pervasive issue of plastic pollution.”

Engineering microorganisms 

By engineering bacteria with an amino acid called 3,4-dihydroxyphenylalanine (DOPA), responsible for mussels’ adhesive properties, the Rice University team enhanced the bacteria’s ability to bind to PET surfaces by modifying it with DOPA. The research development presents a new solution for plastic recycling. 

“Our engineered bacteria are equipped with two ‘weapons.’ One of them is bacteria’s surface protein with DOPA. The other weapon is a protein named PETase,” Zhang explains.

The capabilities of DOPA to combat different types of biofoulings are harnessed by integrating it into intrinsically disordered proteins (Image credit: Rice University).She notes that plastics are big polymers built up by repeated small molecule units. 

“PETase is an enzyme that can hydrolysis these polymers, which work as sharp scissors to break plastic into its small molecule building blocks. Compared to bacteria with only PETase, our engineered bacteria have much more chance to contact and stick to plastic with the assistance of DOPA-containing sticky proteins, therefore, leading to an enhanced efficiency.”

Boosting PET degradation

Zhang shares with us that when the researcher tried to incorporate DOPA into proteins, the challenge was the limited incorporation efficiency and fidelity of the existing incorporation system. 

“Limited efficiency means the protein yield is not satisfied. Limited fidelity means the protein produced by the incorporation system is not homogeneous with only DOPA incorporated, but also with some misincorporation of natural amino acid,” she says.

“To solve this problem, we engineered the DOPA-incorporation system by introducing mutations to the key residues. At the same time, we screened expression conditions for the engineered system to achieve their maximum effect.”Han Xiao, the study leader and director of Rice’s Synthesis X Center and Mengxi Zhang, first author of the study (Image credit: Rice University).

The altered bacteria, tested on PET samples at 37 degrees Celsius, achieved a 400-fold increase in binding to PET surfaces. This cohesive bacteria was united with an enzyme called polyethylene terephthalate hydrolase to break the material into smaller, more manageable fragments, resulting in what the researchers call a large amount of degradation of the plastics overnight.

Last year, researchers at Brunel University, UK, succeeded in developing two new enzymes that degrade PET. They overcame the limitations of previous attempts, which were too slow to be viable at an industrial scale. 

Nobel Prize spotlight

Scientists around the world are now seeking to address plastic pollution at the molecular level, hoping to transform recycling management. This year’s Nobel Prize in Chemistry celebrates the advances in protein research, offering hope for new solutions to tackle plastic waste with enzymes. 

American scientist David Baker, co-recipient of the 2024 Nobel Prize in Chemistry, succeeded in designing a new protein that does not naturally exist. This method can provide a possible solution to plastic pollution. In this case, a protein is designed to attach itself to the plastic molecule, accompanied by chemical compounds to “cut” it.

Demis Hassabis and John Jumper, have also been jointly awarded this year’s Nobel Prize for their development of AlphaFold2, an AI model in predicting the structure of almost all of the 200 million proteins known to science. Researchers can now create images of enzymes that can decompose plastic using their technology.