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The Amazon rainforest has been a poster-child for many aspects of the environmental movement over the past 50 years. Deforestation, soil erosion, land degradation, resource exploitation, anthropogenic climate change and the rights of indigenous peoples are all major issues that have repeatedly brought the world’s largest tropical rainforest to our attention.
It turns out that environmental scientists and activists may have yet another reason to focus their attention on the Amazon: bioremediation. Several years ago, a research team from Yale University took an exploratory trip to the tropical forests of eastern Ecuador with the goal of isolating and characterizing novel species of fungi. Fungi are a diverse group of organisms possessing a range of unique life strategies and metabolic capabilities. They are of major ecological importance in many forest ecosystems as the primary degraders of lignocellulose, a class of carbon-rich biopolymers that make up woody tissue and other tough, structural parts of plants. This research team brought fungal samples back to the lab, cultured them, and set out to grow them on a variety of different carbon sources to figure out how these organisms make a living. What they found was nothing short of astonishing: several strains of endophytic fungi (fungi that live symbiotically within plant tissue, such as endomycorrhizal fungi that associate with plant roots) with the capacity to grow using the plastic polyester polyurethane, or PUR, as their sole carbon source. PUR is a synthetic polymer that is widely used in industry and manufacturing, and is known to most of us in the form of foam insulation or synthetic fibers.
So, maybe don’t bring your Spandex next time you decide to take a trip down to eastern Amazonia.
To me, this discovery poses several interesting questions. The first is, simply, why would an organism have such a capability, to which my knee-jerk response as a biologist is “because there was evolutionary pressure to do so”. This would of course mean that a) something in the environment of these endophytic fungi is similar enough to polyurethane plastic that the PUR-degrading enzymes can also break it down and (more importantly) b) whatever natural compound this PUR-degrading enzyme is meant to degrade is a good enough source of food that a fungus would expend energy and resources producing an enzyme to digest it. The first part of this may not be as surprising as it sounds- plants, particularly in the tropics, produce a host of resins,waxes, and other tough, carbon-rich, chemically recalcitrant (i.e., hard to break down) polymers that are in many ways quite analogous to plastics. But the fact that there are fungi that have seemingly found a niche making a living off such substances, is, to me, highly significant, as it speaks to both the incredible resilience and adaptability of nature in the face of intense resource competition. And nowhere is the competition for resources likely to be more intense than in the world’s most biodiverse forest.
Whether or not the metabolic gift of these plastic-eating fungi could be harnessed for, say, bioremediation purposes, is an open question. But the mere possibility provides another powerful incentive for preserving our forests. Many of the environmental challenges and questions facing human societies today, such as waste management, resource depletion and finding viable non-fossil fuel energy sources, may have analogs and answers waiting for us in the natural world. To deplete and destroy that world without fully exploring the knowledge it has to offer us seems to me to be not just a shameful waste, but a death wish.
“Destroying rainforest for economic gain is like burning a Renaissance painting to cook a meal.” -EO Wilson
PS- I’ve done a bit more research and it turns out the capacity to degrade a synthetic plastic, while remarkable, is not unique to these Amazonian endophytes. In fact, enzymatic degradation of PUR in other fungal species and some bacteria has been observed by research teams around the world.
For more information check out: Russel et al. 2011. Biodegradation of polyester polyurethane by endophytic fungi. Applied and Environmental Microbiology, Vol. 77, No. 17, pp 6076-6084.
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