The benefits and drawbacks of employing bacteria to combat plastic

• Kavyashree Manjunath, a structural biologist, reveals the significant amount of plastic used in her lab.

• Over 65 years, almost 8.3 billion tonnes of plastic have been produced, with less than 10% recycled.

• Scientists are exploring sustainable solutions in their fields, including bacteria that can break down plastics and enzymes that can clean up waste.

• Manjunath discovered natural enzymes that can break down polyethylene terephthalate (PET), a polyester found in many plastic items.

• She founded Apratima Biosolutions, a start-up that can break down 90% of PET waste in 17 hours into products like terephthalic acid and ethylene glycol.

• Manjunath plans to partner with the PET recycling industry to help scale up the technology.

• Microbes are also being used to directly degrade plastic, which are slower but offer some advantages.

• Sukanya Punthambaker and Vaskar Gnyawali developed an approach using a bacterium called X-32 that can degrade PET, polyolefins, and polyamides like nylon.

• They are working on figuring out the enzymes involved to improve their speed and efficiency and plan to test whether their microbe can be scaled up for use at an industrial level.

Biological Solutions for Plastic Degradation

• Jon Pokorski, a nanoengineering professor at the University of California San Diego, is researching biodegradable plastic from scratch. He has developed a method to make thermoplastic polyurethane (TPU) infused with heat-resistant bacterial spores.

• The bacteria degrade 90% of the strips of TPU in a moist, nutrient-rich compost environment.

• Pokorski believes this live-bacteria approach is more feasible for scaling up than pure enzymes.

• The spores serve as a reinforcing additive to the plastic, improving its mechanical properties.

• However, consumer acceptance could be a challenge due to regulatory agencies’ reluctance to use bacteria in plastics.

The Rate-Limitting Step

• Biomolecular engineer Nathan Crook suggests that bacteria can be evolved to become more efficient at breaking down plastic. He discovered a way to attach two previously discovered PET-degrading enzymes onto the surface of a fast-growing bacteria called Vibrio natriegens.

• Crook believes that the rate-limiting step is the enzymes that break down the plastic.

• Challenges include whether the enzyme can be reused and the amount of PET waste loading they will need to optimize.

• Another major challenge is to ensure the enzymes can degrade different kinds of PET waste, including the highly crystalline variety.

Despite challenges, some leading scientists and companies still prefer the enzyme approach. Greg Beckhamm and Carbios have improved one of the PET-degrading enzymes to degrade crystalline PET in water bottles.

• Carbios plans to build a large PET recycling plant to degrade plastic at a larger scale but has postponed it due to a delay in funding.