Plastic-munching bacteria found across the seven seas

Deep within the world’s oceans lurk marine bacteria armed with plastic-munching enzymes, their evolution seemingly sculpted by our synthetic castaways.

A global survey of oceanic life from researchers at KAUST shows that these microbial recyclers are not only widespread, but genetically primed to feast on polyethylene terephthalate (PET), the durable polymer found in everything from soda bottles to clothing^[1].

Their secret weapon is a telltale structural stamp on the PET hydrolase enzyme, known as PETase: the M5 motif.

“The M5 motif acts like a fingerprint that tells us when a PETase is likely to be functional, able to break down PET plastic,” explains Carlos Duarte, a marine ecologist and co-leader of the study. “Its discovery helps us understand how these enzymes evolved from other hydrocarbon-degrading enzymes,” he says. “In the ocean, where carbon is scarce, microbes seem to have fine-tuned these enzymes to make use of this new, human-made carbon source: plastic.”

PET was long deemed practically indestructible in nature. Hopes for biodegradation stirred in 2016, when scientists discovered a bacterium thriving on plastic waste in a Japanese recycling plant. It had evolved an enzyme — a PETase — capable of breaking down the plastic into its constituent parts.

But whether similar enzymes had evolved in the sea remained an open question.

Using a combination of AI-based structural modeling, large-scale genetic screening, and lab experiments, Duarte and his colleagues show that the M5 motif separates bona-fide PET-eaters from biochemical look-alikes. Marine bacteria carrying the full motif shredded PET in lab experiments. Snapshots of gene activity confirmed that M5-PETase genes are vigorously expressed in the world’s oceans, especially in waters riddled with plastic.

To chart the global spread of these enzymes, the team analyzed more than 400 ocean samples from across the seven seas, finding functional versions with the M5 motif in nearly 80 percent of the waters tested — from rubbish-rich surface gyres to nutrient-starved depths two kilometers down. In the latter, the ability to snack on synthetic carbon may confer a crucial survival advantage, according to Intikhab Alam, a senior bioinformatics researcher who co-led the study.

Ecologically, the rise of these enzymes signals an early microbial response to humanity’s planetary littering.

Duarte warns that nature’s cleanup crew works far too slowly to rescue the seas. “By the time plastics reach the deep sea, the risks to marine life and human consumers have already been inflicted,” he says.

On land, however, the discovery could fast-track industrial enzyme design for closed-loop recycling. “The range of PET-degrading enzymes spontaneously evolved in the deep sea provides models to be optimized in the lab for use in efficiently degrading plastics in treatment plants and, eventually, at home,” Duarte notes.

To that end, the M5 motif now offers the blueprint, pinpointing the structural tweaks that matter in real-world conditions, not just in a test tube. If scientists can harness those tweaks, then — as the world gropes for ways to tidy its plastic mess — they may find unlikely allies in the abyss: bacteria that already turn waste into lunch.

Reference

1. Alam, I., Marasco, R., Momin, A.A., Aalismail, N., Laiolo, E., Martin, C., Sanz-Sáez, I., Baltá Foix, B., Sá, E.L., Kamau, A., Guzmán-Vega, F.J., Jamil, T., Acinas, S.G., Gasol, J.M., Gojobori, T., Agusti, S., Daffonchio, D., Arold, S.T. & Duarte, C.M. Widespread distribution of bacteria containing PETases with a functional motif across global oceans. The ISME Journal 19, wraf121 (2025).| article.