The biodegradation of plastic by fungi

Note: all figures regarding plastics in the UK have been sourced from WRAP 

In recent decades the manufacture and consumption of plastics has increased exponentially, with this increase in consumption and manufacture the amount of plastic being sent to landfill has also increased significantly: the amount of plastic waste generated annually in the UK is estimated to be nearly 5 million tonnes with  24% of this currently being recycled and the rest ending up in landfill/incineration or as litter.

During a two-week class trip to the Amazon Rainforest in Ecuador, 2008, Yale student Pria Anand and colleagues collected dozens of endophyte samples from plant stems under the supervision of Yale biochemistry Professor Scott Strobel.  The purpose of the sample collections was to find endophytes that could break down plastics in a process called bioremediation. A subset of the endophytes collected were analysed to assess their ability to degrade polyurethane (a common plastic that is used to make things like insulation, synthetic fibers, plastic for electronics and sealants). Several active organisms were identified during the analysis but only two distinct isolates of Pestalotiopsis microspora were found to efficiently rely upon polyurethane as its carbon “food” resource. However, the fungus (Pestalotiopsis microspora) isn’t the only one to degrade polyurethane (of those collected), but it’s special because it can do so under anaerobic conditions, or without oxygen, said Yale biochemistry Professor Scott Strobel, who oversaw the project.

To summarise, the fungi known only in its scientific form as Pestalotiopsis microspora (among other fungi of the genus Pestalotiopsis) was found to break down the common plastic polyurethane in conditions that lacked oxygen (as well as aerobic conditions). The discovery was made 10 days into the research when Jonathan Russell casually walked into the lab and found one of the petri dishes which contained his experiment had been significantly decomposed.

Scott Strobel, the Yale biochemistry professor who instructed Anand and Russell during these experiments, says because of this discovery, the future looks promising for all types of plastic pollution. He says fungi’s potential to break down man-made materials could be endless, along with its possibilities in medicine and other fields of science.

 Taken from Russell et al 2011

Figure 1 shows the partial decomposition of polyurethane, the degradation was evidenced by a change in medium appearance from opaque to translucent as evident in image B.

Figure 2 Taken from Russell et al 2011

Figure 2 (above) shows PUR-A (Polyurethane) solid agar cultures at 2 weeks after inoculation with the depth of transparency in the tube indicating the degree of degradation.  The research has shown that the endophytes found during the study have great potential in bioremediation projects involving the breakdown of plastics in the future. Due to the process of degradation taking place in anaerobic conditions it has potential to be used in landfills to degrade plastic materials within the landfill itself.

References

Russell, J.R, et al.,2011.Biodegradation of Polyester Polyurethane by Endophytic Fungi. Applied and environmental microbiology. 77(17). pp.6076-6084