Let’s Fix This
Reed biologists develop colonies of bacteria that can break down plastic pollution.
It’s tough, it’s cheap, and it’s every- bacteria on shards of water bottles; where. Polyethylene terephthalate most died, but some stubbornly clung (PET) is found in running shirts, car- to life. Since PET was its only source of pet fibers, curtains, solar panels, ten- nutrition, she reasoned, it had to be nis balls, microwavable containers, and digesting the plastic. (See “Bio Major bottles—about 500 billion bottles are Breeds Microbes That Eat Plastic,” manufactured out of PET every year. Reed Magazine, June 2018.) But the very qualities that make PET Prof. Mellies was thrilled. PET so useful also make it an environmen- is notoriously nonbiodegradable. tal nightmare. Its incredible durabili- Chemically, it is a polymer, consisting ty means that it persists for decades, of long tough strands of ethylene glycol clogging rivers, beaches, forand terephthalic acid monoests, and waterways. Some 8 GO FURTHER mers, all tangled up togethmillion tons of plastic enters Roberts C, Edwards er. These strands lend PET its S, Vague M, Leónthe ocean every year, accord- Zayas durability; they also make it R, Scheffer H, ing to a 2015 paper in Science, Chan G, Swartz NA, virtually impervious to bioJL. 2020. fueling the infamous Pacific Mellies logical reaction. Yet somehow Environmental contrash vortex that is current- sortium containthe bacteria had figured out a ing Pseudomonas ly the size of Texas. way to break it down. and Bacillus speTo get a handle on this gar- cies synergistically With the support of a polyethgantuan problem, research- degrades grant from the National ylene terephthalate ers at Reed are recruiting an plastic. mSphere Science Foundation, Prof. 5:e01151-20. infinitesimal ally. Mellies and a new crop of In a groundbreaking paper students delved deeper into published in mSphere, the open-source the phenomenon. They began by takjournal of the American Society for ing a closer look at the bacteria’s proMicrobiology, Prof. Jay Mellies and duction of hydrolases, enzymes that students at Reed reported on colonies bacteria (and other organisms) use to of bacteria that are capable of breaking digest food. down PET. Remarkably, the colonies do Hydrolases are the molecular equivnot consist of a single species—rath- alent of a pair of scissors, able to chop er, they are composed of a consortium long, complex molecules down to size of five different types of bacteria that so that the bacteria can absorb them. work synergistically to consume PET PET polymers are much longer and and convert it into a source of energy. tougher than any food source bacte“The novelty of our work is that we ria are likely to encounter in the natural are using a group of bacteria to bio- environment. But bacteria are highly degrade PET plastic, whereas most adaptive. Under the right conditions, efforts to date have focused on indi- could a colony boost production of vidual, isolated enzymes for this pur- extra-sharp enzymes and snip through pose,” says Prof. Mellies. the PET? After all, those chains teem The genesis for the project came with high-energy molecules that bacfrom bio major Morgan Vague ’18, teria can use as food. who studied the relationship between Working with 192 separate colobacteria and plastic for her thesis with nies of soil bacteria, the Reed team Prof. Mellies. She dug up samples of spent painstaking months culturing muck from around Galveston Bay in them on PET. The process was agoTexas to see if bacteria there might nizingly slow. But after an eight-week have evolved the ability to feed on trial, the Reed team discovered that hydrocarbons. She tried to culture the PET in one of their samples had
18 Reed Magazine march 2021
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. Ever since 1876, when the German biologist Robert Koch established that the germ Bacillus anthracis was the cause of anthrax, researchers have tended to focus on isolating single organisms so as to pinpoint their properties. But different kinds of microorganisms are often found living together in the environment, and there is reason to think that they can evolve in tandem. Indeed, Prof. Mellies points to a 2001 paper by researchers in Japan who found symbiotic colonies of bacteria flourishing in wastewater. “That was a significant paper,” he says. “I was so grateful to find that.” Having established that their consortium can indeed degrade PET, the Reed 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. —CHRIS LYDGATE ’90
Prof. Jay Mellies [biology] and his students at Reed have grown colonies containing several different types of bacteria that symbiotically degrade the notoriously tough PET polymer.
photo by lauren labarre
Grow an Appetite for Plastic
