Biodegradability of Polyethylene Plastics by Individual and Co-cultured Bacterial Isolates

Plastic has become a permanent feature of the modern world, but its durability is also its greatest environmental flaw. Among the many types of plastic, polyethylene is the most common, used in everything from grocery bags to packaging films. It is made of long chains of carbon and hydrogen atoms that are tightly bound together, making the material incredibly resistant to natural breakdown. Because these chains are so stable and repel water, bacteria and fungi in the soil struggle to recognize them as food. As a result, polyethylene accumulates in landfills and the environment, persisting for decades or even centuries. While burning or burying this waste creates other problems, such as toxic fumes or contaminated soil, scientists have long looked to nature for a solution. The hope is that certain microorganisms might evolve or be found that can break these tough chemical bonds, turning the plastic back into harmless byproducts. This process, known as biodegradation, relies on enzymes—specialized proteins produced by living things—to cut the plastic into smaller pieces that microbes can consume.

In a recent study conducted in Ghana, researchers set out to see if they could find bacteria in local soil that could eat polyethylene, and whether mixing different types of bacteria together would make the process faster. They collected soil samples from three active dumpsites in the city of Kumasi, areas where plastic waste had been piling up for a long time. The team believed that the bacteria living in these specific spots might have already adapted to survive on plastic. They took the soil back to the lab and placed it in containers with shredded pieces of low-density polyethylene, the same material used in common plastic bags. Over several weeks, they let the bacteria grow, selecting only those that seemed to be using the plastic as a food source. Once they isolated these bacteria, they identified them using a high-tech method that analyzes the unique protein signatures of each microbe. They found that the most common bacteria were a type called Bacillus cereus, though they also discovered a few other species, including Achromobacter insolitus and Alcaligenes faecalis.

The researchers then tested how well these bacteria could break down the plastic under different conditions. They wanted to know if the bacteria worked better at certain temperatures, at different levels of acidity or alkalinity, or if they needed more time to do the job. Using a statistical approach to map out these variables, they determined that the bacteria grew best and degraded the plastic most effectively at a moderate temperature of 25 degrees Celsius, in a slightly alkaline environment with a pH of 9, and after about 21 days of incubation. These conditions are relatively mild, suggesting that the bacteria do not need extreme heat or harsh chemicals to function.

To see if working together helped, the team set up experiments where they grew the bacteria alone and in groups. They compared single strains of bacteria against pairs and even triplets of different species living in the same container. The results showed a clear numerical trend where the BC-AI pair achieved the highest mean weight loss (8.04%), followed by other groups, though the statistical analysis revealed no significant differences between the treatments overall. While the actual amount of plastic lost was small—less than 10 percent of the total weight over 28 days—the pattern suggested that the different bacteria might be helping each other. One species might break the plastic into smaller, manageable pieces, while another consumed those pieces, creating a cycle of cooperation that a single type of bacteria could not achieve on its own. Notably, the performance varied among the groups; for instance, the triple culture (BC-AI-AF) showed less weight loss than the BC-AI pair, indicating that more bacteria do not always guarantee better results.

The scientists also looked for the chemical tools the bacteria were using to do this work. They measured the activity of an enzyme called laccase, which is known for its ability to oxidize and break down tough materials. The group with the highest plastic weight loss also produced the highest amount of this enzyme. This connection suggests that the bacteria were indeed chemically attacking the plastic, using their enzymes to weaken the strong bonds holding the polymer chains together. To confirm that the plastic itself had changed, the researchers used a technique called Fourier Transform Infrared Spectroscopy. This method shines infrared light on the plastic to see how its molecular structure responds. They found that the treated plastic showed signs of chemical modification, such as the appearance of oxygen-containing groups on its surface. This indicates that the bacteria had successfully altered the plastic's structure, making it more susceptible to further breakdown.

Despite these promising signs, the study also highlighted the difficulty of the task. The statistical analysis showed that the differences in weight loss between the groups were not large enough to be considered definitively proven within the 28-day timeframe. The plastic is simply very hard to break down, and the changes observed were subtle. However, the combination of physical weight loss, high enzyme activity, and chemical changes in the plastic structure points to a real biological process. The researchers concluded that while a single type of bacteria might struggle to make a dent in polyethylene, a community of different bacteria working together shows much greater potential. They found that these mixed groups did not just attack the plastic randomly; they seemed to coordinate their efforts, targeting different parts of the material's structure in a way that single strains could not.

This work does not offer an immediate solution to the global plastic crisis, nor does it claim to have solved the problem of polyethylene waste. Instead, it provides a clearer picture of how nature might eventually help. It suggests that the key to biodegrading plastic may not lie in finding one super-bacteria, but in understanding how different microbes can cooperate. The study confirms that the bacteria found in Ghanaian dumpsites have the capacity to interact with and modify polyethylene, especially when they are allowed to work as a team. While the process is slow and the results in the lab were modest, the evidence of metabolic cooperation offers a hopeful direction for future research. If scientists can learn to harness these natural partnerships, they may one day develop methods to manage plastic waste that are far more effective than simply burying it or burning it.