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Green gene solution: Breaking down plastics in saltwater using bacteria

Genetically engineered bacteria show success in breaking down microplastics in the world’s oceans.

False color scanning electron micrograph of ''Vibrio vulnificus'' bacteria. Source - CDC/James Gathany (PHIL #7815). Public Domain
False color scanning electron micrograph of ''Vibrio vulnificus'' bacteria. Source - CDC/James Gathany (PHIL #7815). Public Domain

A timely science story for International Microorganism Day. Scientists from North Carolina State University have succeeded in genetically engineering a marine microorganism so that it can break down plastic in salt water. The organism selected for this is Vibrio natriegens,  a halophile that can double in cell number in under 10 minutes (under optimal conditions).

This modified organism can break down polyethylene terephthalate (PET), a plastic used in everything from water bottles to clothing that is a significant contributor to microplastic pollution in oceans. This material is the world’s most common thermoplastic polymer resin.

The bacterium was first isolated from marine sponges of the Saint Martin’s Island Area of the Bay of Bengal, Bangladesh. The goal of the project was to use engineered microbial cells to depolymerize microplastics and then to upcycle those monomers into new polymers or value-added products.

The vast majority of plastic waste is ultimately landfilled or accumulates in the natural environment. This is a consequence of plastic breaking down into microparticles and many of these enter water systems.

For the genetic modification, the scientists took the bacterium Ideonella sakaiensis, which produces enzymes that allow it to break down PET and digest it, an extracted DNA. The gene responsible for breaking down PET was then incorporated into a plasmid.

Plasmids are genetic sequences that can replicate in a cell, independent of the cell’s own chromosome.

By introducing the plasmid containing the I. sakaiensis genes into V. natriegens bacteria, the scientists enabled V. natriegens to produce the desired enzymes on the surface of their cells.

It was then shown experimentally that V. natriegens was able to break down PET in a saltwater environment at room temperature.

The reason for using V. natriegens instead of I. sakaiensis is because V. natriegens has the natural habitat of salt water and plastic pollution in the oceans is the primary concern. In addition, the binary fission rate of V. natriegens makes it very suitable for remediating sites with high levels of plastic pollution.

For the next stage of the research, the aim is to further modify V. natriegens so that the bacterium becomes capable of feeding on the byproducts it produces when it breaks down the PET. It may be possible to modify the V. natriegens organism to produce a desirable end product from the PET, in terms of producing a molecule that is a useful feedstock for the chemical industry.

The research appears in the AIChE Journal, titled “Breakdown of polyethylene therepthalate microplastics under saltwater conditions using engineered Vibrio natriegens.”

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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