Tag Archives: fungi

Amazonian fungi that will eat your plastic

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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.

fairies keep their plants on a tight leash

Beneath the piercingly blue skies of the northern Mongolian steppe, the evidence of fairy activity is plain for all to see. While historically the subject of myths and folklore in medieval European cultures, scientists have recently taken an interest in the mysterious “fairy rings” that occur in woodlands and grasslands across the globe.

What, exactly, is a fairy ring? The term “fairy ring” refers to a ring, ribbon or arc of mushrooms that are the fruiting bodies of an single fungal organism, which branches, just beneath the soil surface, into a mire of thread-like mycelium. That much about fairy rings is relatively straightforward. As research on fairy ring ecology progresses, however, it is becoming clear that the interactions between these fungi and the plants the interact with are incredibly complex and varied.

A typical fairy ring as seen from above ground

Fairy ring fungi can be broadly divided into two classes. “Tethered” fairy rings consist of fungi which form symbiotic associations with tree roots, accessing nutrients for their host tree and gaining carbon in return. Free fairy rings, which occur largely in meadows, do not necessarily work cooperatively with neighboring plants. These fungi produce secrete a broad range of chemical compounds that either stimulate or inhibit the growth of grasses.

Lepsida sordida is one of the most well-studied fairy ring forming fungus, occuring naturally throughout many northern temperate zones. Researchers have identified the chemical compound “AHX” released by L. sordida that acts to stimulate plant growth so strongly that its use in agriculture has been seriously considered. When rice or potatoes are cultivated with a small amount of AHX, the grain yield per plant increased by 25-40%!

Now a group of researchers has revealed another surprise capability of L. sordida– a compound termed “ICA” that also exerts influence over plant growth. In controlled experimental additions, ICA inhibits the growth of grass shoots and roots. This growth-inhibitory effect was also observed when ICA is added to lettuce and rice seedlings.

A plant-growth regulating compound was isolated from a fairy ring forming fungus, Lepista sordida, and its chemical structure was identified as imidazole-4-carboxamide (ICA). Credit: Choi et al. 2010, "Plant-Growth Regulator, Imidazole-4-Carboxamide, Produced by the Fairy Ring Forming Fungus Lepista sordida"

It seems that through the evolution of very specific plant regulatory molecules, fairy rings are able to shape their local environment to suit their needs. The age-old superstitions describing mysterious and sometimes deadly powers of fairy rings  may yet contain some truth.