Researchers in China have discovered a soil bacterium capable of breaking down polyethylene, one of the world’s most widely used and persistent plastics. The finding could offer a new approach to tackling plastic pollution in agricultural lands where plastic mulch films are commonly used.
The study, conducted by researchers at Hangzhou Normal University in Zhejiang Province, identified a bacterium named Bacillus PE4 that naturally degrades plastic waste buried in soil.
Plastic Mulch Creates a Growing Environmental Challenge
Polyethylene is used extensively in agricultural mulch films, grocery bags and packaging materials. Its durability makes it useful for everyday applications but also extremely difficult to decompose in nature.
In farming regions, plastic mulch films are widely used to retain soil moisture and improve crop yields. However, leftover plastic fragments often remain in the soil after harvest, gradually breaking into microplastics that contaminate farmland, waterways and crops.
Scientists have long searched for environmentally friendly ways to deal with this growing problem.
Researchers Looked Beneath the Plastic
Instead of searching for plastic degrading microbes in landfills or oceans, the research team examined soil located directly beneath agricultural plastic mulch.
The scientists collected soil samples from fields where plastic films had been used for years. The samples were mixed with shredded polyethylene and provided with no other food source, forcing any surviving microbes to rely solely on plastic for nutrition.
Five bacterial strains survived the experiment, all belonging to the Bacillus family, which is commonly found in soil.
Bacillus PE4 Emerges as the Most Effective Strain
Among the bacterial strains, Bacillus PE4 showed the strongest ability to break down plastic.
When exposed to thin polyethylene films for 30 days, the bacterium reduced the plastic’s weight by nearly five percent. While the figure may appear small, researchers note that polyethylene can otherwise persist in the environment for hundreds of years without significant degradation.
Microscopic analysis revealed visible cracks, pits and cavities on the plastic surface, indicating active bacterial breakdown.
Optimising Conditions Boosted Plastic Degradation
The research team experimented with different environmental conditions to improve the bacterium’s performance.
By adjusting pH levels, increasing bacterial concentrations and applying heat treatment to the plastic before exposure, researchers significantly enhanced degradation rates.
Under optimal conditions, Bacillus PE4 was able to break down approximately 28 percent of polyethylene within 100 days, a substantial improvement over the initial results.
Enzymes Play a Key Role
Scientists found that the bacterium produced two specific enzymes that became highly active during the plastic degradation process.
Interestingly, these enzymes are normally used to break down tough carbon based compounds found in wood and plant material. Because polyethylene shares some chemical similarities with these natural substances, the enzymes were able to attack the plastic’s carbon backbone as well.
Researchers observed that increased enzyme activity directly corresponded with greater damage to the plastic material.
Potential Applications in Agriculture and Waste Management
The discovery could have important implications for managing agricultural plastic waste and microplastic contamination.
Because Bacillus PE4 can act on both plastic films and powdered plastic particles, scientists believe it may eventually be useful for treating larger plastic waste as well as microplastics already mixed into soil.
Although the bacterium is not yet ready for large scale field applications, researchers say the findings provide a valuable foundation for future work aimed at developing faster and more efficient plastic degrading microbes.
Step Forward in the Fight Against Plastic Pollution
Plastic pollution remains one of the world most challenging environmental problems, with polyethylene accounting for a significant share of global plastic production.
The discovery of Bacillus PE4 demonstrates that nature may already hold solutions hidden in unexpected places. Researchers believe further study of these naturally occurring microbes could help develop sustainable methods for reducing plastic waste and protecting ecosystems from long term contamination.
The study was published in the scientific journal Microbiology Spectrum.