Plastic is cheap, versatile, and used almost everywhere, from packaging and textiles to medical supplies. But unlike natural materials, plastic doesn’t simply decay; instead, it breaks down into smaller fragments called microplastics (<5 mm) and nanoplastics (<1 µm).
These particles persist for decades or longer, accumulate in water bodies, and attract other pollutants like heavy metals, antibiotics, and toxic chemicals. They provide sticky surfaces where bacteria thrive, and recent research shows such surfaces can even host microbes carrying antibiotic resistance genes (ARGs). This raises fears that plastic waste may not only choke ecosystems but also help spread antimicrobial resistance (AMR).
Biodegradation offers a potential way forward. Some microbes produce enzymes capable of disintegrating 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. Yet 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, stretching across India and Bangladesh, is one such environment. It’s the world’s largest mangrove forest and receives around three billion microplastic particles every day through the rivers that feed into the Bay of Bengal. With such heavy exposure, microbes in this ecosystem may have evolved new ways to handle plastic waste. At the same time, because microplastics can carry antibiotics and metals, the same microbes may also acquire resistance traits.
This two-faced possibility — plastic breakdown plus resistance — is at the heart of new work by scientists at the Indian Institute of Science Education and Research (IISER), Kolkata. Published in FEMS Microbiology Letters, it shows that the floating bacterial community in the Sundarbans possesses the genetic tools to degrade plastics and that these tools are also linked with genes for AMR and metal resistance.
The scientists collected one litre of surface water each month for nearly a year (2020-2021) from a site in the Mooriganga estuary, a branch of the Sundarbans. The water samples were filtered to capture microbial cells, and the DNA from these microbes was extracted. Using a technique called metagenomic sequencing, the researchers read the genetic material of the entire microbial community.
Then they compared the DNA sequences to specialised databases. PlasticDB was used to identify plastic-degrading enzyme (PDE) genes while other resources helped detect 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, representing the ability to act on 17 different plastic polymers. Most hits (73%) targeted synthetic plastics such as polyethylene glycol (PEG), polylactic acid, PET, and nylon, while the rest targeted natural polymers like polyhydroxyalkanoates. The single most abundant set of enzymes were those breaking down PEG, suggesting a strong contamination input from biomedical and industrial sources.
The PDEs were more abundant during the monsoon. “HpB reflects the occurrence of PDEs and ARGs per season,” IISER Kolkata biologist and study coauthor Punyasloke Bhadury said this is because “freshwater flow from inland to the coast during monsoon brings in nutrients, bacteria, and other materials including microplastics.”
Crucially, however, the study found that microbes carrying PDEs also often carried resistance genes. Genes for zinc resistance and for resistance to aminoglycoside antibiotics were particularly common among plastic degraders. A co-occurrence network analysis revealed strong associations between PDEs, ARGs, and MRGs, hinting that the same selective pressures — plastic additives, metals, and pollutants — are shaping microbial adaptation.
The findings paint a complex picture. On one hand, the discovery of such a diverse and abundant set of plastic-degrading enzymes is promising. It shows the Sundarbans’ microbial community has already adapted to deal with the flood of plastic waste, potentially offering natural solutions to one of the world’s most pressing environmental challenges.
On the other hand, the very microbes capable of breaking down plastics are also reservoirs of antibiotic and metal resistance genes. If such microbes were deliberately released or enriched in natural settings, they may contribute to the spread of resistance traits, undermining efforts to control AMR. In fact, plastics themselves may serve as hotbeds where resistance genes accumulate and spread between microbes through horizontal gene transfer. This makes the application of plastic-degrading microbes more complicated than it first appears.
“Changing climate can potentially accelerate the transfer of ARGs among bacteria, which may ultimately end up in humans,” Bhadury said. “This could have consequences for One Health and public health in general.”
Madhurima Pattanayak is a freelance science writer and journalist.
Published – August 31, 2025 05:00 am IST
