Genetically modified bacteria may eat up ocean plastic waste

“This is exciting because we need to address plastic pollution in marine environments. One option is to pull the plastic out of the water and put it in a landfill, but that poses challenges of its own. It would be better if we could break these plastics down into products that can be re-used. For that to work, you need an inexpensive way to break the plastic down. Our work here is a big step in that direction,” said Nathan Crook, corresponding author of a paper on the work, in an official release. 

The creation of genetically engineered bacteria

The research team conducted experiments involving two bacterial species: Vibrio natriegens and Ideonella sakaiensis.

Vibrio natriegens primarily inhabits saltwater ecosystems and is notable for its rapid reproduction rate. On the other hand, Ideonella sakaiensis possesses enzymes that give it the power to break down as well as ingest PET quickly, distinct from its. 

As a result, the researchers isolated the genetic sequence from the latter (Ideonella sakaiensis) and integrated it into a plasmid. Plasmids are genetic sequences that may replicate independently within a cell even when it is distinct from the cell's original chromosome.

“In other words, you can sneak a plasmid into a foreign cell, and that cell will carry out the instructions in the plasmid’s DNA. And that’s exactly what the researchers did here,” noted the release. 

The scientists then carefully incorporated the plasmid containing Ideonella sakaiensis genes into Vibrio natriegens bacterium in the lab. The resultant, V. natriegens was able to produce the required enzymes on its cell surface. 

The researchers demonstrated that V. natriegens could degrade PET in a room-temperature-based saltwater setting.

“From a practical standpoint, this is also the first genetically engineered organism that we know capable of breaking down PET microplastics in saltwater. That’s important because it is not economically feasible to remove plastics from the ocean and rinse high concentration salts off before beginning any processes related to breaking the plastic down,” said Tianyu Li, the first author of this new study. 

Three main challenges to address

The researchers emphasize that while this is a significant milestone that has created the essential groundwork, three important challenges need to be addressed before the modified bacteria can operate effectively on a large scale.

Crook concluded: “First, we’d like to incorporate the DNA from I. sakaiensis directly into the genome of V. natriegens, which would make the production of plastic-degrading enzymes a more stable feature of the modified organisms. Second, we need to further modify V. natriegens so that it is capable of feeding on the byproducts it produces when it breaks down the PET. Lastly, we need to modify the V. natriegens to produce a desirable end product from the PET – such as a molecule that is a useful feedstock for the chemical industry.”

The results were reported in the AIChE Journal.

Study abstract:

Poly(ethylene terephthalate) (PET) is a highly recyclable plastic that has been extensively used and manufactured. Like other plastics, PET resists natural degradation, thus accumulating in the environment. Several recycling strategies have been applied to PET, but these tend to result in downcycled products that eventually end up in landfills. This accumulation of landfilled PET waste contributes to the formation of microplastics, which pose a serious threat to marine life and ecosystems, and potentially to human health. To address this issue, our project leveraged synthetic biology to develop a whole-cell biocatalyst capable of depolymerizing PET in seawater environments by using the fast-growing, nonpathogenic, moderate halophile Vibrio natriegens. By leveraging a two-enzyme system—comprising a chimera of IsPETase and IsMHETase from Ideonella sakaiensis—displayed on V. natriegens, we constructed whole-cell catalysts that depolymerize PET and convert it into its monomers in salt-containing media and at a temperature of 30°C.