Small Things Considered

Staph And Cholesterol: An Odd Couple

by Elio

Cholesterol and MRSAs vie for headlines. Both are formidable topics of enormous interest to readers of mass media and to scientists (many of whom read mass media, probably in the bathroom). It turns out that Staphylococcus aureus and arteriosclerosis have something in common, although not in the way you might think. It happens that the yellowish-golden pigment of S. aureus is made by a pathway that, in its early steps, resembles the one for making steroids.

Let’s back up a moment. The S. aureus pigment is a carotenoid called staphyloxanthin. Although the discoverer of the organism, the Scottish surgeon Alexander Ogston, coined its species name in 1880, the role of the pigment has only been recently uncovered. It is essential for the virulence of the organism, acting as an antioxidant that detoxifies host-produced reactive oxygen species, such as O₂^–, ·OH, and HOCl. Mutants lacking the pigment are much less virulent. Sounds like blocking the synthesis of staphyloxanthin would be a good way to combat staph infections, no?

The pathways for making staphyloxanthin and steroids. Source

A Red Letter Day (on Merry's calendar)

by Merry

Not every one makes it to the age of 80. And of those who do, only a precious few are still doing what they love. Elio's 80th birthday is this Saturday, April 26. He told me to restrain my eloquence here, but to see him at 80, still being a learner as well as a teacher, publicly writing and speaking about The Small Things, and enjoying life—well, that's an inspiration for me. Happy birthday, Elio! Mazel tov!

On Being 80

by Elio

Long ago, I thought that reaching 72 years of age would be a reasonable accomplishment, as this would bring me into the new millennium. Done, some time ago. I now have no mileposts in mind, just a still horizon. If anything, it’s this blog that counts. So, let me tell you why this has been and continues to be such an exhilarating, if demanding, experience. I will quote from the very last part of my book, In the Company of Mushrooms. I still like the sound of it and hope that it will help explain my interest in mushrooms, as well as microbes. Before doing that, I want to thank my collaborator, Merry, without whom the task would be far more arduous.

I am a microbiologist by profession, now near the completion of my career. When I collect and study mushrooms, however, I do not act as a professional biologist. Most of what I love about mushrooms and how they fit in people’s lives is far remote from my research and teaching. My life in science has been spent at the laboratory bench: I studied how bacteria grow and make their DNA. I am of the generation that witnessed the beginning of molecular biology and its offspring, genetic engineering. It was only after my career was established that I stepped into the world of forests, pastures, and mushrooms.

Still Life with Mushrooms, Insects and Amphibians. Otto Marseus Van Schrieck,
Dutch (1662). Herzog Anton Ulrich-Museum. Braunschweig, Germany

The distance between these two interests—microbiology and mushrooms—may not appear to be very fundamental to a non-scientist, but it is in fact quite considerable.

Play It Again, Cyan

by Merry

Differential interference contrast
image of P. chromatophora.
Source: Micro*scope

The evidence is quite compelling. All plastids (photosynthetic organelles and non-photosynthetic kin) are thought to be descended from one cyanobacterium that was engulfed by one unicellular heterotrophic eukaryote approximately one billion years ago. The descendents of that host are today's green algae (and plants), red algae, and glaucophytes (a group of microscopic freshwater algae). Several other eukaryote lineages acquired plastids second-hand by engulfing a plastid-containing red or green alga (a process called secondary symbiosis to distinguish it from the original primary symbiosis). For an interesting review of the convoluted history of plastid acquisition, click here.

Granted, it is not a simple matter to transform one’s lunch into a well-behaved photosynthetic organelle, but still one wonders why this appears to have happened only once, especially since plastid acquisition by secondary symbiosis—also not a simple thing to do—has occurred several times. Still, for some reason(s), only one eukaryote has managed to transform a cyanobacterium into a photosynthetic cellular entity.

Or so it was thought...

Talmudic Question #31

Many unicellular protists have a very complex body plan. One can find “legs” (see our posting on Euplotidium), “mouths,” food vacuoles, etc. Some of these structures reflect the feeding habits of the organisms. The question arises, why haven’t they have become multicellular?

Some Like It Linear

by Merry

Last year, a team of Japanese researchers deliberately converted the circular chromosome of E. coli into a linear one. To do this, they borrowed some tricks from the lambdoid coliphage N15, a temperate dsDNA phage whose prophage exists and replicates as a 46 kb linear plasmid. When tested in L broth at 37°C, the modified E. coli were indistinguishable from wild-type in terms of growth rate, nucleoid appearance, and overall pattern of transcription—provided that the linearization occurred at or near the chromosome replication terminus.

Should we be surprised?

Feed From the Hand That Bites You

If you look for them, you'll find them—bacteria that can feed on antibiotics, that is. Here, looking means to make an enrichment culture using a medium whose single carbon source is an antibiotic. Add a soil sample with its resident bacteria and look to see who, if anyone, will grow. As reported in a recent issue of Science, researchers collected soil samples from 11 environments, including some very unlikely to have had any exposure to human-made antibiotics. They tested each soil sample against 18 antibiotics, some natural and some human-made. There were no zero scores.

A Letter From Bob Murray

A frequent commentator to this blog, Prof. Murray has as much experience with prokaryotic systematics and cell biology as anyone we know.

Source: Strata Resource, Inc.

A program on the English language stimulated my looking at my copy of Johnson’s Dictionary and by accident reading part of the Preface. A paragraph seemed singularly appropriate to the bloggery we had on "species" and the need to classify the ones that are identified. When that is done, as in Bergey’s Manual, one makes a sort of dictionary defining names and the person who does it is a lexicographer (called a "dull drudge" by Johnson!). So here it is:

When I took the first survey of my undertaking, I found our speech copious without order, and energetick without rules; wherever I turned my view, there was complexity to be disentangled, and confusion to be regulated; choice was to be made out of boundless variety, without any established principle of selection; adulterations were to be detected, without a settled test of purity; and modes of expression to be rejected or received, without the suffrages of any writers of classical reputation or acknowledged authority.

Well, that seems to say everything about the problem of dealing with either words or bacteria and leaves usage to be considered in the doing. I think it is a very appropriate association of efforts a few centuries apart.

And a comment…

The Bile Salt Giveth and the Bile Salt Taketh Away

Clostridium difficile. Color-enhanced scanning
electron micrograph by Dave McCarthy and
Annie Cavanagh. Source: Wellcome Image Awards

We needn’t be reminded that pathogenic microbiology is a branch of microbial ecology but a nice example helps makes the point. The story is about a nasty disease, pseudomembranous colitis, which affects mainly immunocompromised people who have been on antibiotics and are lying in a hospital bed. The disease, as the name suggests, is an inflammation of the large intestine accompanied by the formation of a membrane-like fibrin deposit that lines the surface of the gut. The usual culprit is an anaerobic sporeformer, Clostridium difficile. Most people do not normally harbor C. difficile, although many infants and young adults do so without any problem. When the normal gut biota is reduced by antibiotics, C. difficile grows and produces toxins that are responsible for the pathology. Actually, the typical outcome of this infection is not pseudomembranous colitis, but, more often, diarrhea.

Being a sporeformer, C. difficile is insensitive to common disinfectants and thus can survive on hospital surfaces to become the cause of the next infection. Strong agents are required to kill the spores, e.g., bleach. But what causes the disease to erupt?