Small Things Considered

Fine Reading: Yet Another Reason to Appreciate Fungi

by Elio

This blog, known as it for taking up the cause of the underdog, was fortified by reading How Fungi Have Shaped Our Understanding of Mammalian Immunology in a recent issue of Cell Host and Microbe. Not only that, but this is an exceptional piece of reviewing. It’s short (a mere three pages), fun to read, and to the point.

So, what’s the case for fungi shaping our understanding of immunology? (Note the inclusion of “mammalian” in the title. A nice departure from the customary anthropocentricity). The author, Gordon Brown of Aberdeen, guides us through both early and late developments, starting with Elie Metchnikoff, the discoverer of phagocytosis who saw yeast cells being engulfed by the water flea Daphnia, through C-type lectins, Toll and Toll-like receptors, and intracellular signal pathways.

Selected seminal discoveries from 1884 to 2006 are shown along with representative images,
including Metchnikoff (1884); zymosan engulfment by PMN (1941); properdin (1954, trimeric
structure); Aspergillus infection in TLR-deficient Drosophila (1996); fungal recognition by
Dectin-1-expressing fibroblasts (2001); collaborative signaling between TLR and CLRs (2003);
ITAM-like motifs and Syk kinase recruitment (2005); the requirement of multiple PRRs for
optimal anti-Candida responses (2006); and enhanced Candida infection in the kidneys of
CARD9^−/− mice (2006). Source.

In the author’s words: …fungi and their components have long been known to influence immune function, and the contributions made from the study of fungal infections are often underappreciated. Well, here’s for trying.

A Condominium Plant

A section of a stem of L. a. africana. The swollen
section to the left is a domatium showing the entry
slit created by the resident ants, Petalomyrmex phylax.
Arrows point to worker ants. Source.

by Merry

Early in childhood, we learned that the plants and animals around us are discrete entities with definite boundaries. A dog might have fleas, but fleas and dogs are separate and distinct individuals. With our increased familiarity with symbioses—especially those of the obligate sort—have come many instances where "separate" individuals can seemingly survive only as part of a functioning association. Here is yet another example.

For more than twenty-five years, Doyle Mckey, now a professor in ecology, University of Montpellier II, France, has been studying one species of tree, Leonardoxa africana africana (Fabaceae or Leguminosae)—known locally as the bush-boer bean. Likely you've never seen one of them as they are found only in a narrow strip of humid coastal rain forest in southern Cameroon. This particular tree is a myrmecophyte, i.e., an ant-plant. (For those who relish words as we do, myrmecophyte is from the ancient Greek myrmeco, "ant" and phyton, "plant." Myrmecophyte is not to be confused with myrmecophile, a general term for any organism that lives in association with ants, or with the Myrmecophila, a genus of myrmecophytic orchids.)

It Was The Worst of Times, It Was the Best of Times

by Elio

At the end of the Permian period, about 250 million years ago and not long before the dinosaurs appeared, life on Earth experienced its greatest catastrophe: a mass extinction that did away with the vast majority of life forms on land and sea. The question arises, who ate the carcasses of the deceased? Surely bacteria and protozoa digested the animal corpses, most likely reaching unusually high population sizes as the result. But who took care of the masses of dead plant material? Fungi are quite good at digesting plants, especially woody plants. So, did the fungi also become prevalent after the catastrophe?

Five Questions About Microsporidia

Preface by Elio

Bacteria, archaea, microfungi, and many protists are "mainstream" in the sense that everyone in our business is aware of them. Other highly consequential microbes such as the microsporidia and the oomycetes commonly elicit reactions such as "I really should look into them sometime." I have been a microbiologist for upward of sixty years but have paid only the scantest attention to these large and important groups of organisms (and therefore hang my head in shame). But it's never too late to correct such oversights. We are starting out by reproducing, with permission of the author, a particularly illuminating article on the microsporidia by Patrick Keeling.

by Patrick Keeling

What Are Microsporidia?

Microsporidia are a diverse group of obligate intracellular eukaryotic parasites. There are approximately 1,300 formally described species in 160 genera [1], but this certainly represents a tiny fraction of the real diversity because most potential host lineages have been poorly surveyed. Nearly all microsporidia are known to infect animals, and some are responsible for a number of human diseases (13 species of microsporidia have been documented to infect humans) predominantly associated with immune suppression [2]. They also infect several commercially important animal species such as bees, silk worms, and salmon, and various domesticated mammals. They are thought to be especially common in insects and fish, although most invertebrates have been so poorly surveyed this may change.

Figure 1. Light micrograph of Antonospora locustae with pressure-
induced polar tube eversion. The scale bar is 10 µm. (A) Many
ungerminated spores (one example labeled U) and a few germinated
spores, showing the residual spore wall (one example labeled G).
(B) A germinated spore where the everted polar tube (PT) has
extended far from the cell and can be seen to be many times the
length of the spore.

Their infective stage is a thick-walled spore, which is also the only stage that can survive outside their host cell [3]. The spore contains a sophisticated infection apparatus, primarily distinguished by a long, coiled filament called the polar filament. When the spore germinates, an inflow of water leads to pressure in the spore that eventually ruptures the wall and forces the polar filament to eject, turning inside out to form a tube (Figure 1) [4]. This process takes place very quickly, so the polar tube is in effect a projectile. At the completion of germination, the parasite cytoplasm is forced through the tube and either delivered to the surface of the host cell, or perhaps injected into the host cytoplasm if the projectile tube has actually penetrated the host cell. It has also been shown that microsporidia can be taken up by phagocytosis, and then use the polar tube to escape from the vacuole [5], so there appear to be more than one mode of infection.

Are They Protists, Fungi, or What?

There has been considerable debate about the origin of microsporidian parasites. Aside from their elaborate infection mechanism, they have few distinguishing features, and have thus been difficult to compare to other eukaryotes. This is illustrated by their tumultuous taxonomic history (Figure 2), and the tendency to lump them with what we now know to be unrelated organisms. When microsporidia were discovered in 1857, they were considered to be schizomycete fungi, but this was an artificial group that included various yeasts and bacteria. They were soon transferred to Sporozoa and ultimately to the subgroup Cnidosporidia. This too was a grab-bag of four unrelated groups (Microsporidia, Myxosporidia, Actinosporidia, and Helicosporidia) that were falsely grouped because of their intracellular parasitic way of life. Remarkably, Microsporidia, Myxosporidia, and Helicosporidia have since been shown to be fungi, animals, and green algae, respectively, underscoring just how distantly related these parasites really are.

Fiddling with Fungi: And the Winner Is…

by Elio

X. longipes. Source.

Late in August of 2008 we promised to update you on the attempts to out-Stradivarius Stradivarius by crafting violins made from wood treated with fungi. Here is the latest news.

Scientists at the Swiss Federal Laboratories for Materials Testing and Research made violins from wood treated with two different fungi: Physisporinus vitreus for the spruce top plate and Xylaria longipes (aka Dead Man's Fingers) for the sycamore bottom plate. The treatment lasted six or nine months, by which time the wood had become covered with a fuzzy growth of mycelium.

Small Friends of Fungi

This article first appeared in the splendid Cornell Mushroom Blog. Reading it, we were jolted into realizing that we had a distorted view of the living world, no less. Like most people, we believed that in natural habitats, some animals eat plants, those animals are eaten by predators, and that's about it. We thank Bob Mesibov for setting us straight. We are delighted to share his insights with you by reproducing his article here, with permission from him and from Kathie Hodge, editor and blogificator of the Cornell Mushroom Blog.

by Bob Mesibov

The millipede Narceus americanus photographed by
Kent Loeffler, copyright Cornell University. You can
find this borescopic image among the many in the
book Beneath Notice: Adventures with a Borescope
by Kent Loeffler, with "Fungal Outbursts" by Kathie
Hodges.

If you studied the traditional sort of biology, you're probably carrying around an unfortunate prejudice.

You see terrestrial habitats as a simplified nutrients-and-energy pyramid. At the bottom are green plants, feeding on sunlight, carbon dioxide and soil water and minerals. Next layer up on the pyramid is the herbivore mob: leaf and stem eaters, sapsuckers, root nibblers, seed and fruit gobblers. Above these green feeders are a couple of layers of predators. And that about sums up the world, right?

Wrong. That's only part of the world, and a small, very specialised part of it, too.

All for One, and One for All!

by Mark Martin

Panic grass growing well at a soil temperature
of over 50 °C (123 °F). Source.

When I recently attended the Sixth International Symbiosis Society Congress in Madison, Wisconsin, I was awed by the fascinating forms that symbiotic relationships take among diverse organisms. One talk that particularly intrigued me was from the laboratory of Marilyn Roossinck of the Samuel Roberts Nobel Foundation in Oklahoma, which described the mutualistic relationship between a virus, an endophytic fungus, a monocot, and elevated temperatures in geothermal soils. It also made me consider how readily we seem to associate the word "virus" with pathogenic associations, when nature is often far more subtle when it comes to mutualistic partnerships.

The story began in 2002 when it was found that a type of grass growing in the geothermal zones of Yellowstone National Park—panic grass, Dichanthelium lanuginosum—was able to survive intermittent high temperatures in geothermal soils (up to 65 °C.) due to its association with an endophytic fungus, Curvularia protuberata. The fungus is essential to the plant's ability to tolerate temperatures that are lethal to the non-colonized plant. Panic grass, incidentally, has nothing to do with botanical phobias; instead, the name derives from the Latin panicum, referring to foxtail millet.

Mycodiesel

This is the fourth (and final) post for this year's Week of the Fungi on STC, a sporadic undertaking. This annual festival is our way to hail the start of the fall mushroom collecting season in parts of our home territory (the northern hemisphere).

Colorized environmental SEM photo
of Gliocladium roseum. Source.

by Elio

Huge amounts of money and effort are going into making automotive fuels using biological processes, but a fully satisfactory answer is not yet at hand. Well, fungi may come to the rescue. Strobel et al. found that a fungus called Gliocladium roseum actually makes a complex mixture of volatile hydrocarbons and derivatives that resemble those found in diesel fuels. Not only that, this fungus decomposes cellulose without needing any help. It sounds just right, but before you talk to your broker about your Exxon Mobile stock, read on.

Fungal Stars in the Forest Dark

This is the third post for this year's Week of the Fungi on STC, a sporadic undertaking. This annual festival is our way to hail the start of the fall mushroom collecting season in parts of our home territory (the northern hemisphere).

Mycena lux-coeli, a Japanese fungus
photographed by its own light. Source.

by Elio

Fungi, along with selected bacteria and invertebrates, are included in the list of bioluminescent organisms. These fungi are pretty unique because, unlike the other light-emitting organisms, fungi don't walk, swim, or fly. Thus, the usual explanations for bioluminescence (e.g., attraction, repulsion, communication) do not seem to apply. Dispersing spores is a central preoccupation among mushrooms, so one can guess that the light may facilitate visits by animals that could help in this process. Plus, as Dennis Desjardin writes in a news item from the NSF, some may well glow to attract the predators of insects that eat the mushrooms...befriend the enemy of your enemy!

A Thing of Beauty

This is the second post for this year's Week of the Fungi on STC, a sporadic undertaking. This annual festival is our way to hail the start of the fall mushroom collecting season in parts of our home territory (the northern hemisphere).

The entombed springtail with numerous
conidiophores. Source.

by Elio

A thing of beauty is a joy for ever:
Its loveliness increases; it will never
Pass into nothingness…
      from Endymoin, by John Keats (1878)

Close-up of the conidiophores. Bar = 50 μm.
Source.

We can attest to these truths through a lone piece of amber. Between 50 and 35 million years ago, a springtail (Collembola) got stuck in some resin, probably from a conifer. Before it could free itself, more resin dripped on it, eventually entombing it completely. In time, the resin became amber, but before that happened, a fungus grew on the insect's cadaver, sprouting numerous spore-bearing structures (conidiophores). Fortunately, this piece of amber found its way to two paleomycologists, Heinrich Dörfelt and Alexander Schmidt, who readily identified the fungus as a member of the genus Aspergillus.