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A common soil fungus (Purpureocillium lilacinum BA1S), when combined with calcium and mild alkalinity, speeds up the breakdown of biodegradable plastic (PBAT), offering a greener path for managing agricultural and packaging waste.

Biodegradable plastics such as poly(butylene adipate-co-terephthalate) (PBAT) are often promoted as eco-friendly alternatives to conventional plastics. However, in real soil or composting environments, PBAT can take months or even years to fully decompose.

To tackle this challenge, Prof. Chi-Te Liu's lab at Institute of Biotechnology, National Taiwan University (NTU), in collaboration with Prof. Shih-Shun Lin (Institute of Biotechnology, NTU), Dr. Sheng-Lung Chang (Industrial Technology Research Institute, ITRI, Taiwan) and Prof. Ting-Jang Lu (Institute of Food Science and Technology, NTU), investigated how environmental factors can enhance the ability of soil fungi to break down this stubborn material. The study is in the Journal of Hazardous Materials.

The team focused on the Purpureocillium lilacinum strain BA1S, a soil fungus previously isolated by Ph.D. student Wei-Sung Tseng, the first author of this study, from farmland in Taiwan. This fungus is known for producing enzymes that are capable of degrading complex polymers. Instead of modifying the fungus genetically or using expensive chemical additives, the researchers tested a simple but effective approach—adjusting the pH of the environment and adding calcium salts.

They discovered that combining mildly alkaline conditions (pH 7.5) with calcium ions greatly boosted PBAT degradation. Under these optimized conditions, the fungus decomposed more than half of the plastic film—about 55% weight loss—in just two weeks.

Using microscopy and spectroscopy, the researchers confirmed that the fungal treatment caused deep surface erosion and chemical changes to the plastic. To explore what was happening inside the cells, they performed transcriptomic and gene-network analyses.

The results showed that genes related to biosurfactant production, membrane transport, and protein degradation were highly activated, while genes responsible for basic energy metabolism were downregulated. This indicates that the fungus redirected its metabolism toward breaking down and absorbing plastic fragments.

Further biochemical tests revealed that calcium ions not only promoted enzyme secretion but also enhanced the stability of a key degrading enzyme, a cutinase known as PlCut. In laboratory assays, calcium improved PlCut's thermostability and reduced its thermal inactivation, enabling the enzyme to work longer and more efficiently.

This study sheds new light on how environmental conditions can strengthen microbial degradation of biodegradable plastics. It also demonstrates that fine-tuning natural factors—such as pH and mineral availability—can be a simple, low-cost, and sustainable way to improve plastic biodegradation in soil and composting systems.

"By showing that a simple adjustment in pH and calcium availability can activate a fungus's full degradation potential, our work opens new possibilities for greener waste management and circular-economy applications," says Prof. Chi-Te Liu, corresponding author of the study.