Tag Archives: Amazon

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.

Saharan dust fertilizes new world rainforests

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As winds sweep eastward into the Atlantic off the northwest African coast, a remarkable thing happens: plumes of aeolian dust particles are swept off the surface of the Sahara. They will meander along the varied paths of the easterly trade winds, only to settle again in places as remote from each other as they are from the source: North America, the Caribbean, the Amazon Basin, the southern Mediterranean, eastern Europe, and occasionally even the chilly southern shores of Scandinavia.

A major Saharan dust plume event, November 1988

Where does the dust come from? Total Ozone Mapping Spectrometer (TOMS) suggest two major source areas: the Bodélé depression at the southern edge of the Sahara and an area covering eastern Mauritania, Western Mali and southern Algeria.

A little bit of dust blowing around shouldn’t be anything for meteorologists to bother about.  This dust, however, is anything but inconsequential- in the Caribbean alone, an estimated 20 million tones are deposited annually. It is the primary source of several essential trace elements, such as calcium and magnesium, to island rain forests whose soils have been leached through tens of thousands of years of erosion. Saharan dust enters the Amazon basin in bursts accompanying major wet season rains, feeding the soil with nutrients that the forest depends on. In fact, scientists now believe the Amazon to be so dependent on aeolian dust inputs that efforts are underway to model long-term expansions and contractions of the world’s largest rain forest in relation to the size of the Sahara over geologic time.

Dust not only nourishes the forests, it moderates their climates. African mineral dust is now considered the dominant light scattering aerosol throughout the tropical and subtropical Atlantic. The ability of airborne dust particles to scatter light decreases the amount of direct solar radiation hitting earth’s surface around the equator.

The dependence of major ecosystems across the world on Saharan dust underscores the deep connectivity of the biosphere, atmosphere, lithosphere and hydrosphere.

The world’s largest rainforest is nourished by mineral dust blown from across the Atlantic

1.Goudie, A. & Middleton, N. Saharan dust storms: nature and consequences. EARTH-SCIENCE REVIEWS 56, 179-204 (2001).

2.    SWAP, R., GARSTANG, M., GRECO, S., TALBOT, R. & KALLBERG, P. SAHARAN DUST IN THE AMAZON BASIN. TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY 44, 133-149 (1992).

sunset in the tropics

I was so struck by this description of watching the sun wane through the forest in eastern Amazonia that I just had to share. E.O Wilson is an ecologist blessed with an amazing gift for rendering what most of us consider to be insignificant details of the world into beautiful, potent truths.

“At Berhnardsdorp the sun passed behind a small cloud and the woodland darkened. For a moment all that marvelous environment was leveled and subdued. The sun came out again and shattered the vegetative surfaces into light-based niches. They included intensely lighted leaf tops and the tops of miniature canyons cutting vertically through tree bark to create shadowed depths two or three centimeters below. The light filtered down from above as it does in the sea, giving out permanently in the lowermost recesses of buttressed tree trunks and penetralia of the soil and rotting leaves. As the light’s intensity rose and fell with the transit of the sun, silverfish, beetles, spiders, bark lice, and other creatures were summoned from their sanctuaries and retreated back in alternation. They responded according to rerceptor thresholds built into their eyes and brains, filtering devices that differ from one kind of animal to another. By such inborn controls the species imposed a kind of prudent self-discipline.”

— In Biophilia, by E.O. Wilson– an ecologist, entomologist, professor and acclaimed science writer