Plastic is cheap, versatile, and used in almost everything from packaging and textiles to medical supplies. But unlike natural materials, plastic doesn’t just break down; instead, it breaks down into smaller fragments called microplastics (<5 mm) and nanoplastics (<1 µm).
These particles persist for decades or longer, accumulating in water bodies and attracting other pollutants such as heavy metals, antibiotics and toxic chemicals. They provide sticky surfaces on which bacteria thrive, and recent research suggests that such surfaces can even host microbes carrying antibiotic resistance genes (ARGS). This raises fears that plastic waste could not only choke ecosystems but also help spread antimicrobial resistance (AMR).
Biodegradation offers a potential way forward. Some microbes produce enzymes that can break down the strong chemical bonds in plastic polymers. A famous example is petase, discovered in Ideonella sakaiensis , which can degrade polyethylene terephthalate (PET), a common plastic used in bottles. Despite such exciting discoveries, natural microbial communities with this ability remain poorly understood, especially in environments where plastic pollution is constant and intense.
The Sundarbans, which stretches across India and Bangladesh, is one such environment. It is the world’s largest mangrove forest and receives an estimated three billion microplastic particles each day via rivers that empty into the Bay of Bengal. With such heavy exposure, microbes in this ecosystem may have developed new ways to process plastic waste. At the same time, because microplastics can carry antibiotics and metals, those same microbes can also acquire resistance traits.
This dual capability—plastic breakdown plus resistance—is the basis of new work by scientists at the Indian Institute of Science Education and Research (IISER) in Kolkata. Published in FEMS Microbiology Letters , it shows that a floating bacterial community in the Sundarbans has the genetic tools to break down plastic, and that these tools are also linked to genes for AMR and metal resistance.
The scientists collected one liter of surface water every month for almost a year (2020-2021) from the Mooriganga Estuary site, a branch of the Sundarbans. The water samples were filtered to capture microbial cells, and DNA was extracted from these microbes. Using a technique called metagenomic sequencing, the researchers read the genetic material of the entire microbial community.
They then compared the DNA sequences to specialized databases. The PlasticsDB was used to identify plastic-degrading enzyme (PDE) genes, while other resources helped uncover args, metal resistance genes (MRGs), and mobile genetic elements—pieces of DNA that allow genes to move between microbes.
The analysis revealed an impressive 838 hits for plastic-degrading enzymes, reflecting the ability to handle 17 different plastic polymers. The majority of hits (73%) targeted synthetic plastics such as polyethylene glycol (PEG), polylactic acid, PET and nylon, while the remainder targeted natural polymers such as polyhydroxyalkanoates. The single most abundant set of enzymes were those that degraded pinning, suggesting a strong input of pollution from biomedical and industrial sources.
PDE was more abundant during the monsoon. “The HPB reflects the seasonal occurrence of PDE and argus,” said Punyasloke Bhadury, a biologist and researcher at IIS Kolkata, adding that this is because “freshwater flow from inland to the coast during the monsoon brings nutrients, bacteria and other materials, including microplastics.”
Crucially, however, the study found that microbes that contain PDEs also often carry resistance genes. Genes for zinc resistance and resistance to aminoglycoside antibiotics were particularly prevalent in plastic degraders. Co-production network analysis revealed close relationships between PDEs, ARGS, and MRGs, suggesting that the same selective pressures—plastic additives, metals, and pollutants—are driving microbial adaptation.
The results paint a complex picture. On the one hand, the discovery of such a diverse and abundant set of plastic-degrading enzymes is promising. It shows that the Sundarbans microbial community has already adapted to the flood of plastic waste, potentially offering natural solutions to one of the world’s most pressing environmental problems.
On the other hand, the microbes that can break down plastic are themselves reservoirs of antibiotic and metal resistance genes. If such microbes were deliberately released or enriched in natural settings, they could contribute to the spread of resistance traits, undermining efforts to control AMR. In fact, plastics themselves can serve as hotbeds in which resistance genes accumulate and spread among microbes through horizontal gene transfer. This makes the application of plastic-degrading microbes more difficult than it first appears.
“Climate change could potentially accelerate the transmission of arguables in bacteria that could eventually reach humans,” Bhaduri said. “This could have implications for individual health and public health as a whole.”
Madhurima Pattanayak is a freelance science writer and journalist.
Published – August 31, 2025 at 05:00 IST
