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)

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« January 2011 | Main | March 2011 »

February 28, 2011

Farmer Joe Dictyostelium

by Elio


A scanning electron micrograph showing the various stages of
transformation of Dictyostelium. Each body represents a different
stage in the process. Hundreds of thousands of single cells
aggregate to form a migrating “slug” (lower left). Once the slug
comes to a stop, it gradually elongates to form the fruiting body.
[Courtesy of M. J. Grimsom & R. L. Blanton, Texas Tech Univer-
sity]. Source.

The practice of agriculture is not limited to humans: ants, termites, and snails all grow fungi, and who knows who else do something similar. But not many have claimed that such activities are to be found among simpler organisms. Now we have a report that slime molds have also gone down the road to agriculture. Dictyostelium discoideum, the best studied of the cellular slime molds, is a social amoeba that thrives by grazing on bacteria. Given ample bacterial food, these organisms grow as single cells. When food becomes scarce, they aggregate into pretty, differentiated fruiting bodies (called sorus, plural sori) consisting of a round mass of spores held up by a stalk. The spores eventually become dispersed, to repeat the cycle at a new site. The entire epic can be viewed in a dramatic documentary available here. (This movie is narrated in German, giving you the opportunity to hone your skills in that language.)

Continue reading "Farmer Joe Dictyostelium" »

February 24, 2011

Pop Quiz

by Elio

Parlez-vous Biologie? In this spirit, we thought you might enjoy taking a quiz that tests your familiarity with terms of biology. To check your answer, you can get a definition of each of the terms by clicking on them. Many are from our column Of Terms in Biology, some from other posts, and a couple are just related bystanders. Here’s our scoring sheet:

26-30 — Magnifique
21-25 — Trés bon
16-20 — Pas mal
11-15 — Comme ci, comme ça
5-10 — Tant pis
0-4 — Bon voyage

Continue reading "Pop Quiz" »

February 21, 2011

Candida's Unstable Chromosomes & Unorthodox Sex

by Dean Dawson


Candida albicans. Source.

Who hasn't heard of Candida? It’s one of the most common fungal pathogens of humans. It is also a commensal organism, living mainly in people’s gastrointestinal tract. The diseases it causes range from a fairly mild vaginitis to deadly opportunistic systemic infections. In fact, Candida species are a major cause of nosocomial bloodstream infections. Candidas are close relatives of the baker’s yeast, Saccharomyces cerevisiae, but live by very different rules.

Candida has been the focus of intense research at the molecular level for only the past fifteen years or so, and it has not been an easy road. These organisms, it turns out, have a slightly different genetic code than most others, rendering the standard molecular tools less useful. Additionally, Candida does not exhibit the mating and spore formation behaviors of its cousins Saccharomyces cerevisiae and Aspergillus, which made them popular organisms for fast-moving molecular genetic studies. But the development of new tools and a growing community of researchers have revealed in the past few years that Candida has evolved its own unorthodox mechanisms and lifestyles that probably greatly enhance its ability to adapt to changes in its host environments.

Continue reading "Candida's Unstable Chromosomes & Unorthodox Sex" »

February 17, 2011

Worms Have Viruses, Too!

Once again, we take pleasure in translating and sharing a post from the blog by Manuel Sánchez, Curiosidades de la Microbiología.

by Manuel Sánchez

When we highlight the importance of viruses in ecosystems, we usually assume that all living things, multi- or unicellular, can be infected by at least one kind of virus. This is not a far-fetched assumption, but one that until now has had to endure some notable exceptions. Viruses had not been found in certain groups of living organisms, notably the nematodes, the group that includes the model organism Caenorhabditis elegans.

This era is officially over now, as a couple of viruses have been described that infect these worms. In an article in PLOS Biology, the authors report that they have isolated and characterized viral agents. And they did it in the old-school way. Briefly, take a handful of worms, grind them up, filter the extract through a 0.2 µ filter, inject uninfected worms with this filtrate, and look for pathology. Marianne Felix, the first author, tried this and noticed that the worms got sick and could not be cured with antibiotics.

Continue reading "Worms Have Viruses, Too!" »

February 14, 2011

The Great Epidemic

by Merry Youle


The "Redwood of the East." Source.

When you read the title—The Great Epidemic—what came to mind? The Black Death (Yersinia pestis) that in two years killed 20 million people in Europe—approximately 30-60% of the population? The 1918 flu pandemic with its tally of 50 million dead in three years? AIDS, with a death toll projected to reach 200 million by 2025? Or perhaps that 20th century epidemic that struck down over three and a half billion in North America in the space of a few decades—the American chestnut blight? These chestnut trees, Castanea dentata to be precise, were stately giants often 100 feet or more in height with crowns that spanned 100 feet. Their straight trunks provided billions of dollars worth of beautiful, rot-resistant wood, and the bountiful nuts provided far more than the traditional stuffing for Thanksgiving turkeys. Combined they had made up a quarter of the forest canopy from Maine to Mississippi.

Continue reading "The Great Epidemic" »

February 10, 2011

Talmudic Question #71

As NASA’s hotshot exobiologist, you are asked to design an Earth satellite system in which some organism(s) can live actively (i.e.. no spores) for millennia. How would you go about it? Specify an orbit of your choice.

February 07, 2011

Highlights of 2010

by Elio and Mark (Martin)

We asked friends and colleagues to point to papers published in 2010 that tickled their fancy. Here are their responses.

Michael Yarmolinsky

An article published in 2010 that strikes me as particularly noteworthy is ATP control of dynamic P1 ParA-DNA interactions: a key role for the nucleoid in plasmid partition by Vecchiarelli, Han,Tan, M Mizuuchi, Ghirlando, Biertümpfel, Funnell, and Mizuuchi.


Click here to view an animation of the
action of ParC and Par M in plasmid R100
segregation. Source.

The orderly segregation (partition) of plasmids and many bacterial chromosomes is achieved with the aid of a par operon of two structural genes and a site on the DNA to which one of the two Par proteins binds. The other Par protein, involved in autoregulation of the operon, is an ATPase of either the Walker type or actin-like. Despite the simplicity of these systems, their mechanisms of action have long remained obscure. Partition involving an actin-like ATPase was finally elucidated in a striking paper published in 2007 by Garner, Campbell, Weibel, and Mullins. Only in 2010 was a cogent explanation offered for the mechanism of genome partition mediated by the Par system with an ATPase of the Walker type.

Continue reading "Highlights of 2010" »

February 03, 2011

Of Terms in Biology: Colloids

by Stefan Klumpp

Milk is a colloid. Source.

Colloid may not be a common term in biology these days, but in the early 20th century, colloids were believed to hold the key to the secrets of life. So what is a colloid? According to the Encyclopaedia Britannica     it is any substance consisting of particles substantially larger than atoms or ordinary molecules but too small to be visible to the unaided eye; more broadly, any substance, including thin films and fibers, having at least one dimension in this general size range, which encompasses about 10−7 to 10−3 cm. Thus, these are nanoparticles ranging from 1 nm to 10 µm. This upper size limit is relatively high, as other definitions set it at 1 µm or as too small to be studied with a light microscope.

This definition is very inclusive, encompassing not only true globular nanoparticles but also fibers and membranes that may be mere nanometers long in one or two spatial dimensions but much bigger in the others. Many colloids by this definition are not considered to be such by those who study them. One example is a bacterial culture that consists of particles (cells) 1 µm in size, but which is rarely called a colloid (except maybe in studies of the physical properties of the culture as a complex fluid). And there are some ambiguities. For example, whereas a colloid by that definition is a substance that consists of small particles, in physics the small particles themselves are often called colloids. Also, 'colloid' often implies that the small particles are dispersed in a fluid, although that is not required by this definition. Lastly, 'colloid' is often used to describe a state of matter that consists of small particles, thus emphasizing that in principle anything can be made colloidal by splitting it into appropriately sized particles and suspending them in a solvent. Reflecting these ambiguities, many people are more comfortable using the adjective 'colloidal' instead of the noun 'colloid,' as in colloidal system, colloidal state, colloidal domain, colloidal suspension, etc.

Continue reading "Of Terms in Biology: Colloids" »

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