Plastic-Eating Microbes Work Better in Teams

Plastic pollution has spread across the land and into the deepest parts of the ocean. Many plastics contain additives such as phthalic acid esters (PAEs), which act as plasticizers to make materials more flexible. But as plastic waste accumulates, these chemicals can leach into the environment, where they have been linked to endocrine disruption.

Although researchers have identified microbes capable of breaking down plastics, using them to clean polluted environments has proved challenging. Microbial digestion is often slow, it sometimes requires extreme temperatures, and many strains can degrade only a single type of plastic. In principle, a combination of different species with an appetite for plastic could tackle bioremediation more effectively than any one microbe alone.

Motivated by this idea, researchers from the Helmholtz Centre for Environmental Research (UFZ) studied how a bacterial consortium might collectively degrade plastics. Their findings, published in Frontiers in Microbiology, showed that three bacterial species work together by ‘cross-feeding,’ where one microbe releases metabolic byproducts that another takes up as nutrients, to break down PAEs.¹ Alone, these microbes could not degrade plastic. “Introducing these bacteria into polluted natural environments, a process known as bioaugmentation, could potentially help reduce PAE contamination in real-world settings,” said coauthor and microbiologist Hermann Heipieper at UFZ, in a press release.

To find plastic-eating microbes, the researchers didn’t look far: They collected a biofilm sample from the polyurethane tubing of their laboratory’s bioreactor. Then, the team incubated the microbes in a growth medium using the PAE model compound diethyl phthalate (DEP), as the carbon and energy source.

Next, 16S ribosomal RNA sequencing revealed that the biofilm contained three different species: one species each from the Pseudomonas putida and Pseudomonas fluorescens groups and an unknown Microbacterium species. Notably, these individual bacterial species could not degrade plastic compounds alone; instead, it was a team effort.

To further characterize the microbes’ DEP degradation, the researchers used metaproteomic analysis and found that the microbes break down plastic like a relay team passing the baton. First, the Microbacterium species initiates the degradation of DEP and generates key intermediary products: monoethyl phthalate and phthalate. Then, the Pseudomonas strains, whose proteomic analysis revealed they have pathways capable of cleaving the other byproducts, continue the process. This method of feeding is known as cross-feeding. While it is common in nature, it had not been demonstrated in plastic-eating bacteria before, according to the researchers.

Besides DEP, the researchers found that this team of microbes could digest other common PAEs: dimethyl phthalate, dipropyl phthalate, and dibutyl phthalate. Excited by the potential value of this consortium, Heipieper remarked in the statement, “The next step will be to test our new consortium in actual wastewater samples containing microplastics, to assess its ability to remove PAEs.”