Small Things Considered

Talmudic Question #42

Given that horizontal gene transfer between and among prokaryotes seems to be a relatively frequent occurrence, why does it appear to be so rare between prokaryotes and eukaryotes (except perhaps in early times)?

The Secrets of the Sacculus

by Hans H. Martin

Isolated peptidoglycan sacculi from Aqua-
spirillum serpens.

In my retirement, one topic that continues to interest me is the 3D-structure of murein (i.e., peptidogylcan, as is now generally preferred in the literature). I participated in the isolation and description of the "murein sacculus," the "little sac" of E. coli B, under the directorship of Wolfhard Weidel in Tübingen, Germany, in the late 1950's and early 60's. An old review (Bag-shaped Macromolecules: A New Outlook on Bacterial Cell Walls) presented the concept that the bacterial exoskeleton is "a rigid bag of the shape and volume of the cell" in the form of "one enormous macromolecule kept together by covalent bonds throughout." The authors included a simple hypothetical model for the structure of the sacculus.

During the past 40 years, a considerable number of increasingly sophisticated and ingenious studies of 3D-peptidoglycan structure have been presented and different models have been proposed. Regular or irregular, parallel or perpendicular orientation of peptidoglycan strands to the cell surface were considered. (For three more recent papers, click here, here, and here.) But invariably, the authors have accepted that this is "one of the most important, yet still unsolved, structural problems in biochemistry." They concluded that "there is a shortage of methods by which to determine precisely, by direct structural analysis, the tertiary structure of peptidoglycan." However, very recently Grant Jensen and co-workers at Caltech reported an important advance in visualizing structural details in peptidoglycan from Gram-negative bacteria.

Of Terms in Biology: Synteny

Source

Geneticists are known for having developed a language of their own. So is just about everybody else in science. Ergo, looking up definitions is often a necessity. Today’s term is synteny (which etymologically means “on the same ribbon”). You might think that we don't need worry about this so much in bacteria and archaea, the majority of whom have a single chromosome. All their genes are syntenic by definition. Synteny applies to multichromosomal organisms—of which there is a sizeable number within the bacteria, e.g., Rhodobacter spheroides (where this was first observed), Burkholderia cepacia, and some vibrios, brucellas, leptospiras, and rhizobia. Anyhow, we went ahead and looked up synteny. We were hoping for some enlightenment to share with you. Were we successful? Here are the results.

The Two Edges of the Antibiotic Sword

by Joshua Fierer

Scanning Electron Micrograph of Enterococcus
faecalis. Image credit: CDC/Pete Wardell. Source

Antibiotics transformed medicine. For almost the first time in history, they made it possible to medically cure diseases (granted, surgeons were able to cure some people before the antibiotic era began, little more than half a century ago). However, when someone takes an antibiotic aimed, let’s say, at an E. coli causing a urinary tract infection, every bacterium in that person’s body is placed under selective pressure. Within a short time, the body is repopulated with antibiotic-resistant strains. The broader the spectrum of the antibiotic, the more cataclysmic the change in our microflora. Sometimes this has devastating consequences, such as the patient becoming super-infected with highly resistant bacteria. But, it turns out, antibiotics do more than that: they indirectly compromise a component of the innate immune defense.

Two by Two

Two years ago, Elio began this blog. It was a couple of months before Merry realized what Elio was up to and jumped on board. The first article was on the circadian rhythm of cyanobacteria: It Don't Mean a Thing If It Ain’t Got That Swing, a topic we’ll revisit soon.

These two years, it’s fair to say, have provided proof positive of the tenacious excitement of the microbial world. More than 230 posts later, we still feel that excitement, still strive to share it. In one sense at least, this has been easy. Day after day, new tales show up that occasion our appreciation and delight. Short of stories to share with you? No way!

Sexually Avoided Disease

by Willie Wilson

True color satellite image of a milky E. huxleyi
bloom in the English Channel, south of Plymouth,
UK, on 30 July 1999. This bloom was effectively
‘dead’ and up to 1 million E. huxleyi-specific
coccolithoviruses per teaspoon of water were
found in the middle of the high-reflectance
water. Courtesy of the Plymouth Marine Labora-
tory Remote Sensing Group.

The Red Queen’s race in Lewis Carroll’s Alice in Wonderland is a common metaphor for an evolutionary arms race. A good example can be seen in predator-prey dynamics, particularly virus-host interactions where hosts must rapidly evolve immunity to infection for survival of the species. It takes all the running you can do to stay in the same place.

Red Queen dynamics can also help explain the bloom-bust cycles of oceanic algae that can be seen readily from space in satellite images. One such alga is Emiliania huxleyi, a 5 µm diameter eukaryotic cell that has an elaborate armory of calcareous coccoliths. It is ubiquitous in the world’s oceans and forms dense milky blooms that cover vast areas of mainly temperate oceans. Until recently, the mechanisms of E. huxleyi bloom disintegration were poorly understood, but it is now accepted that viruses (referred to as coccolithoviruses) are intrinsically linked to these sudden crashes.