Prof. Jay Mellies and students at Reed have reported on colonies of bacteria that can break down PET. Remarkably, the colonies do not consist of a single species—rather, they are composed of a consortium of five different types of bacteria that work synergistically to consume PET and convert it into a source of energy.
“The novelty of our work is that we are using a group of bacteria to biodegrade PET plastic, whereas most efforts to date have focused on individual, isolated enzymes for this purpose,” says Prof. Mellies.
The genesis for the project came from bio major Morgan Vague ’18, who studied the relationship between bacteria and plastic for her thesis with Prof. Mellies. She dug up samples of muck from around Galveston Bay in Texas to see if bacteria there might have evolved the ability to feed on hydrocarbons. She tried to culture bacteria on shards of water bottles; most died, but some stubbornly clung to life. Since PET was its only source of nutrition, she reasoned, it had to be digesting the plastic.
Prof. Mellies was thrilled. PET is notoriously nonbiodegradable. Chemically, it is a polymer, consisting of long tough strands of ethylene glycol and terephthalic acid monomers, all tangled up together. These strands lend PET its durability; they also make it virtually impervious to biological reaction. Yet somehow the bacteria had figured out a way to break it down.
Microbial Symbiosis at Work
With the support of a grant from the National Science Foundation, Prof. Mellies and a new crop of students delved deeper into the phenomenon. They began by taking a closer look at the bacteria’s production of hydrolases, enzymes that bacteria (and other organisms) use to digest food.
Working with 192 separate colonies of soil bacteria, the Reed team spent painstaking months culturing them on PET. The process was agonizingly slow. But after an eight-week trial, they discovered that the PET in one of their samples had lost 3% of its mass. The bacteria had eaten it. Under the microscope, the students saw tiny holes where the microbes had chewed through the PET.
More remarkable still, the successful sample contained five different strains of bacteria living cheek by jowl, with some strains breaking down the PET into components that other strains could digest, and so on.
“
These bacteria are cooperating,” says Prof. Mellies. “
It’s crazy, but they’re working together to degrade the polymers.”
The concept of microbial symbiosis isn’t exactly new, but it represents a new frontier in microbiology. Having established that their consortium can indeed degrade PET, the Reed College team is now focused on the next step: finding ways to make the process more efficient. The genetic pathways underlying hydrolase production and PET degradation are still not fully understood, but with new tools such as metagenomic sequencing, Prof. Mellies is convinced that Reed students can boost production of enzymes that break down PET and hasten the bacteria’s evolution. The potential upside is huge—not only for fighting pollution, but also for harnessing microbial symbiosis for other problems.
Source: Reed College