Moselio Schaechter


  • The purpose of this blog is to share my appreciation for the width and depth of the microbial activities on this planet. I will emphasize the unusual and the unexpected phenomena for which I have a special fascination... (more)

    For the memoirs of my first 21 years of life, click here.

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February 17, 2014

The Fungus That Killed Darwin’s Frog

by Gemma Reguera

A Mouthful of Kids

Figure1 Figure 1. A ‘pregnant’ male Darwin frog carries its babies in the vocal pouch (left) until they are big enough to be spat out (right). Sources here and here.

In his second expedition to South America, Darwin discovered many new species of animals and plants. The field observations obtained throughout this 5-year expedition provided the intellectual framework for the maturation of his ideas on evolution. It also introduced the world to a tiny (2-3 cm in length) frog known as Darwin’s frog. The group includes the northern (Rhinoderma rufum) and the southern (Rhinoderma darwinii) species, which inhabit the central and southern forests of Chile (and adjacent areas of Argentina), respectively. As in many other amphibians, fecundation is external. However, Darwin’s frogs do not leave the fecundated eggs on the ground and exposed to environmental insults and predators. The males scoop them with their mouths and incubate them in their vocal sac. The dedicated dads feed their offspring after the eggs hatch, producing secretions analogous to milk that allow the tadpoles to grow in a protected environment, sometimes until they have fully developed into froglets. When the young are mature enough to fend for themselves, the male frog literally spits them out. You can see a short video describing this amazing reproductive strategy following this link. This behavior, generally known as neomelia, allows the male ‘surrogates’ to care for the eggs and then the young, maximizing survival throughout the critical tadpole stage. Unfortunately, deforestation in the regions inhabited by these frogs has resulted in vast habitat losses, leaving Darwin’s frogs in precarious conditions. The last sight of a northern Darwin frog was reported in 1980, leading researchers to suspect that this particular species went extinct years ago. The species has been tagged as ‘possibly extinct’. The southern species, R. darwinii, which has traditionally occupied a much larger region, has been able to survive, but population numbers have declined dramatically.

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November 08, 2013

A Whiff of Gastronomy

by Elio

Figure1 Fig. 1. The black truffle Tuber melanosporum. Source.

Ah, truffles! They are the gourmet’s celebration, the cook’s inspiration, the common man’s anticipation. And they demand quite a price, which at last count hovered around $2,000 a pound for Italian white truffles, the French black truffles being cheaper, but still not within the reach of most people. And their production is decreasing. So it befalls few mortals to dine on these delicacies. But there is hope. As many of you know, truffle oil is used quite widely in restaurants. So, where does truffle oil come from? Did it ever see a truffle? Before going there, let’s agree that the price is right. You can find all sorts of truffle oil on the Internet for as little as $5 per ounce. It even comes in a kosher variety.

 

Figure2
Fig. 2. 2,4 Dithiapentane.

Alas, truffle oil has not been within smelling distance of a real truffle but is simply some sort of regular vegetable oil, often olive oil, that has been doctored by the addition of the ether, 2,4 dithiapentane. This is one of the main odor-producing compounds in truffles and, to a debatable approximation, it emulates the real aroma. Many expert food connoisseurs disagree and maintain that it doesn’t resemble the real thing. Also, some are bothered by the artificial nature of this concoction. In defense of truffle oil, the flavor it imparts to food is quite impressive. It does remind me of the taste of the few truffles I have been lucky enough to eat—metallic, pungent, earthy, and very distinctive. It may not be the real thing but it does contribute a nice bite to otherwise uninspired dishes. I, for one, am on the side of the folks who enjoy it. The only allowance needed is to agree that even an imitation may taste good.

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November 06, 2013

Count Your Mushrooms

by Elio

This is the second installment of this year's Fungus Week, our more-or-less annual celebration of this exciting realm of life.

Figure2
Fig. 1. Species and genera of fungi identified from 454-sequencing data in 100 Norway spruce logs. The inner part of the wheel represents the genera and the outer part the species with at least 90% probability of correct identification. Source.

Maybe you have to be a mushroom enthusiast or a fungal ecologist to give this a thought, but counting the number of mushrooms in a tract of forest will not tell you the size of the fungal biomass therein. The mushrooms you see are only the fruit bodies. The whole fungal organism consists of an extensive growth and accumulation of invisible hyphae, the mycelium. Measuring fungi by counting mushrooms is like weighing an orchard by counting the apples on apple trees, only here not all “trees” produce fruit. To the consternation of wild mushroom collectors, the copious amounts of mycelial filaments existing in the soil and decaying wood may or may not produce mushrooms. What determines which mycelia will fruit, and how prolifically? In earlier times, this conundrum seemed difficult to unravel, but now, with high throughput sequencing available, this has become amenable to investigation.

A group of Norwegian and Finnish researchers carried out an intensive study to correlate the number of fruit bodies emerging from decaying tree logs with the abundance of the mycelia in the wood. The general conclusion was that for most fungal species, the more mycelial mass at a site, the greater the number of visible fruit bodies. This may not seem surprising, but the details, based on careful measurements, matter. For example, fewer fruit bodies were produced by those species whose fruiting is more energetically costly, such as the ones that display a cap sticking out from the surface of a tree (called pileated in the trade) as compared to those whose fruit bodies lie flat along the surface (known as resupinate). The quantities of both mycelial DNA and visible fruit bodies increased linearly with the increasing decay of the wood until the decay became quite advanced. From that point on, the amount of mycelial DNA continued to increase, whereas the fruit body count decreased. In other words, the mycelium goes on developing as the tree decays but this does not result in the concomitant formation of fruit bodies. These fungi find growing easier than differentiating under these conditions.

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November 04, 2013

Radiation Ahead? Eat a Black Mushroom!

Week of the Fungi on STC is a sporadic undertaking. This occasional festival is our way to hail the fall mushroom collecting season in parts of the northern hemisphere. We are a bit late this year, but mushroom collecting is still possible in many parts.

by Elio

Figure1
Fig. 1. Left: Auricularia-auricula-judae (Judas’ ear, tree ear, jelly ear). Source. Right: Boletus edulis (porcini, cep, king bolete). Source.

Suppose that one day you have the misfortune to receive a strong dose of radiation in preparation for a medical procedure, say a bone marrow transplant. To your surprise, the physician prescribes that you eat a hefty serving of dark-colored mushrooms about an hour beforehand. Lest you think this black magic, the clinician explains that this has been proven effective in 'clinical trials' in mice, surprisingly so in fact. A 2012 paper with the forbidding title Compton Scattering by Internal Shields Based on Melanin-Containing Mushrooms Provides Protection of Gastrointestinal Tract from Ionizing Radiation describes this work. The authors fed mice a mushroom used in East Asian cuisine, called Judas’ ear, tree, or jelly ear (Auricularia auricula-judae) an hour before giving them a powerful 9 Gy dose with the beta emitter Cesium137. For perspective, anything over ~0.1 Gy is considered a dangerously high dose for humans. All the control mice died in 13 days while ~90% of the mushroom-fed ones survived. Mice fed a white mushroom (porcini) died almost as fast as the controls, but those fed white mushrooms supplemented with melanin also survived.

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May 02, 2013

Little Known Glomalin, a Key Protein in Soils

by Elio

Figure1
A visible portion of the rhizosphere. Source.

If you had heard of glomalin, you are a better person than I am. Until a couple of months ago I wasn’t aware of its existence, which is close to sinful: it happens to be a very abundant protein in the soil rhizosphere, playing a key role in the soil’s mechanical properties and as repository of soil carbon. Glomalin is a glycoprotein (although the “glyco-“ may be overused here, as biochemical analyses suggest that it contains little in the way of sugars) that binds together silt, sand, or clay soil particles. By ‘supergluing’ the small, loose particles, this gooey protein makes larger granules or aggregates and protect the soils from the eroding forces of winds and water. So, where does glomalin come from? It is thought to be made by fungi, more specifically by members of the arbuscular mycorrhizal fungi, the Glomales (hence the name ‘glomalin’). The hyphae of these fungi synthesize glomalin as part of their stress response. They coat their outer surface with the protein to make a protective waxy coat that keeps the water and nutrients inside the cells. The glomalin coating also makes the fungal strings sticky so they bind soil particles, thus creating an protective ‘armor’ against environmental insults and microbial predators. Most importantly, the fungal “string bags” make soil aggregates. This improves water infiltration and retention in the soils and gas exchange, which makes them more fertile. For more information on glomalin click here.

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January 28, 2013

Domestic Just for the Sake of it – The Evolution of a Fungus with Good Taste

by Daniel P. Haeusser

We know quite a bit about how the wild aurochs or their ilk evolved into tame, bossy cows and how the insignificant grass teosinte became nutritious maize, but what do we know about the evolution of microbes involved in food and drink production? For thousands of years before the advent of microbiology, our ancestors used microbes for this purpose without knowledge of the contributions or the domestic origins of these small workhorses. Even today, when microbes continue in key roles during food and beverage production, we know far less about their evolution of domestication than we do for the process in animals or plants.

Why should that matter? Obviously, we humans would like to encourage microbes that benefit us and hinder microbes that harm us. The key to this is understanding what evolutionary routes can lead to one state or the other and how they can be purposefully altered to favor the benefits.

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October 25, 2012

Fungal Meningitis Bulletin

by Elio

Figure1
Exserohilum rostratum conidia. Source: AP Photo/CDC

We seldom post items of immediacy, but here we interrupt our leisurely ways to write about the current disastrous meningitis outbreak caused by the injection of fungus-contaminated steroids and other drugs. As microbiologists, the question comes to mind at once: Who is the pathogen? The fungus implicated is Exserohilum rostratum (although a couple of cases were due to the more familiar Aspergillus fumigatus and to a Cladosporium). Like many good fungi, E. rostratum has a couple of synonyms: Setosphaeria rostrata and Helminthosporium rostratum. If you never heard of them, you’re in good company. Neither had an expert on fungal infections who I asked, nor had I despite occasional dealings with fungi. The reason is that there are lots of species of such molds, many of which cause exceedingly rare human diseases.

E. rostratum is one of the dematiaceous or darkly pigmented molds that is found in soil, on plants and in stagnant water. Like many molds, it can be identified under the microscope by the morphology of its conidia (asexual spores), which are quite distinctive. The rare human infections it causes are typically of external body sites, e.g., the skin, cornea. Being common in the environment, it is likely that it contaminated the injectable medications before they were packaged.

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July 23, 2012

An Evolutionary Tale of Zombie Ants and Fungal Villains & Knights

by Gemma Reguera

Infected ant with spore stalk

Fig. 1: An ant infected by O. unilateralis bites the underside of a
leaf. The fungal stroma emerges from the back of the ant’s head and
develops a fruiting body with a capsule full of spores. Once matured,
the capsule is released and the spores disperse on the forest floor.
Courtesy of David P. Hughes. Source.

In a recent post I shared with you some amazing things I had learnt about coprophilous (‘dung-loving’) fungi that spit their spores like pros. What I did not tell you then is that my six-year-old son also fell in love with the spitting fungi (dung + spit = child’s interest!) and wanted to learn more. So we spent hours watching online videos until we stumbled upon a BBC’s Planet Earth video narrated by the great David Attenborough about ant parasitic fungi in the genus Cordyceps. The video shows a carpenter ant (genus Camponotus) that has been infected by spores of the fungus Ophiocordyceps unilateralis. The spores germinate inside the ant’s respiratory track and the mycelia grow towards the brain while feeding on soft tissues. Once the fungus reaches the brain, it induces behavioral changes such that the ant climbs up vegetation and bites the underside of the leaves. There the ant awaits its death while the fungus continues to grow within. The stroma stalk of the fungus eventually protrudes from the back of the ant’s head and a fruiting body bearing a capsule filled with spores forms near its tip (Fig. 1). Once the spores are sexually mature, the capsule is released, and then explodes, either in the air or upon hitting the ground. This delivers the spores into the path of healthy ants, there to start a new cycle of infection.

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April 26, 2012

What Is This Link to Mushrooms in Works of Art?

by Elio

Pseudo fardella

Pseudo Fardella, Italian, active in Tuscany second half, 17th
century. A Basket of Cherries, Apples, Plums, Chestnuts,
Asparagus and Porcini on a Ledge.
Private collection.

On the left side of this blog, in amongst the Blogroll links, is a somewhat strange entry, “Mushrooms in Works of Art.” I’ll save you the trouble of clicking on it. This is the website of a registry that lists works of art, mainly Western, that display mushrooms. Now, why would anyone care about this? The project started about 10 years ago when mycologist Hanns Kreisel from Greifswald University in Germany and chemist Tjakko Stijve from Switzerland and I came together, impelled by the same thought, which was that depictions of mushrooms in art would give us some insight into their relationship to people of various times and cultures.

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November 17, 2011

Is a Good Offense the Best Defense?

by Merry Youle

3.1.4_fungi_2

The budding yeast, S. cerevisiae. © Eye of Science/
Photo Researchers, Inc. Used with permission. Source.

Most eukaryotes possess an RNA interference system (RNAi) that they use to regulate gene expression and to defend against viruses and other mobile elements. However, some budding yeasts, such as Saccharomyces cerevisiae, appear to get along just fine without it even though RNAi has benefited other yeasts by silencing transposons in particular. How do these yeasts that lack functional RNAi systems compete with closely related species that do? And how come they don’t have RNAi when RNAi arose in an early eukaryote ancestor and is conserved throughout most of the fungi?

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  • We welcome readers to answer queries and comment on our musings. To leave a comment or view others, remarks, click the "Comments" link in red following each blog post. We also occasionally publish guest blog posts from microbiologists, students, and others with a relevant story to share. If you are interested in authoring an article, please email us at elios179 at gmail dot com.

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