Small Things Considered

'tis the 30th of November...

...and today we celebrate the first anniversary of this blog. It’s been fun (and considerable work). We thank all who have contributed by writing articles, commenting, and visiting.

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Shining More Light on LOVs - An Update

EM image of a dividing C. crescentus.
The upper cell has a holdfast, the
structure involved in adhesion; the
lower one, a flagellum. Source:
MicrobeWiki

We recently posted a piece on Brucella abortus becoming more virulent when grown in the light, a puzzling finding if there ever was one. Like many other forms of life, B. abortus has a flavin-binding light-sensitive protein domain called LOV that is responsible for this phenomenon. So far, not many other functions can be attributed to LOV in bacteria, but one has come to light recently in a report from Sean Crosson's lab. In Caulobacter crescentus, a favorite of students of bacterial differentiation, LOV is involved in the attachment of the cells to various surfaces as well as to each other. Here, the LOV is a domain within LovK, a histidine kinase that is part of a two-component signaling system. Shining blue light on the organisms results in greater attachment, as evidenced by the cells aggregating to form large rosettes. The authors propose that "light is an environmental signal that can cue the Caulobacter cell on where it is positioned in the water column." Blue light penetrates water to a greater depth, thus providing an especially strong signal. Sticking to surfaces such as nutritional detritus may be a good thing─keeping food close at hand.

Surely, this is but one of many findings that will come to light from people doing such illuminating experiments.

Wayward Locomotive

EM of a section through
M. pneumoniae showing a
terminal organelle. Source:
Atlas, R. M. Principles of
Microbiology, 2nd Ed.

Poor wand'ring one!
Though thou hast surely strayed...
                Pirates of Penzance by Gilbert and Sullivan

Mycoplasma have good press agents. They frequently make the news these days, often because they have the smallest genomes of any free-living organism and, mirabile dictu, because their genome has been transplanted into a willing "anucleate" recipient, creating the first "synthetic cell." You might think that small means simple, but not so. Qualities of these organisms surpass their elephantine brethren in both complexity and fascination. Here is but one example of mycoplasmal ascendancy...

Some mycoplasmas, such as M. pneumoniae, move by gliding, using a mechanism that may well be unique to this group of organisms. At the leading end of the cell, they have a complex structure termed the terminal organelle that is involved not only in motility, but also in cell adherence and even cell division.

Fossil Fats

by Tanja Bosak

In the beginning, there were fats, and in the end, only fats will remain. This is, in simple words, the basis of a new field of research: the study of molecular fossils. Molecular fossils are remnants of the actual lipid molecules that formed the cell membranes of ancient organisms. Because all organisms have membranes, most old fats may not tell us anything more than that some living organisms were present in the past. Fortunately, relatives of a disreputable lipid─cholesterol─are more informative and come to the geochemist's rescue. Old fats, it turns out, also contain various cholesterol-like ringed lipids (called polycyclic terpenoids) that are amazingly stable under both acidic and basic conditions, at elevated temperatures, and when faced with other adverse conditions that destroy most organic compounds in sediments. By some estimates, the mass of five-ringed terpenoids in sedimentary rocks and oil reservoirs (~10¹² tons) is comparable to the total mass of carbon in all living organisms! (1).

Just as the shape of a fossil bone can tell us whether an organism was a dinosaur or a mammal, chemical structures of various polycyclic terpenoids may be specific to certain microbes or environmental conditions.

Talmudic Question #24

Why didn't mitochondria and chloroplasts cede all of their DNA to the nucleus, as did most hydrogenosomes and certain other organelles? 

Microbial Sociology

Beauty can be complex.
Improvisation 31.
Wassily Kandinsky (1913)

Few topics of recent have been as titillating as communication among bacteria.  Just like insects, bacteria "talk" to each other in a chemical language, asking one another questions such as: How many of us are there? Is it time to make a biofilm? Do conditions call for making toxins? and (the grandfather of them all) Should we turn on the light? Most of the time, the conversation doesn't get started until the population density has reached a threshold level─why debate the issue if you don't have a quorum? Thus, "quorum sensing" is the apt term used for this linguistic skill.

Typically, the messages communicated impact the individual first, and only later the group. Ultimately, a species may well gain from, say, the timely making of a biofilm, but each cell that plays this game may get an immediate reward. There are instances when the message is less benign. E. coli cells, it turns out, sometimes also tell each other when it's time for some of them to commit suicide. One interpretation is that this happens in times of nutritional or other stresses; the dying bacteria lyse, releasing nutrients that can benefit their compatriots.

An Ancient Fungus On A Fungus On A Fungus

Cap of a mushroom in amber named Palaeo-
agaracites antiquus covered with mycelium of a
parasite, Mycetophagites atrebora. Bar = 0.5 mm.
Source

Sometimes the title says it all. Evidence of mycoparasitism and hypermycoparasitism in Early Cretaceous amber tells you: (a) that the authors are talking about something that took place some 100 million years ago, and (b) that there are several layers of parasitism in the specimen in question. So, what is this specimen in question? It turns out to be a mushroom encased in amber, currently the oldest known fossil mushroom (having bested the previous record holder, another mushroom preserved in amber).

Special Delivery ─ Eukaryote Style

by Merry

Plasmodium falciparum exiting
erythrocytes. Credit: College of
Medicine, University of Florida

Type III secretion, the mechanism that introduces bacterial proteins into eukaryote host cells, rates among the most exciting themes of modern pathogenic microbiology. What makes it fascinating is both its biomechanics (it makes use of a fancy nanotechnology needle-like device) and its strategic aspects (the delivered proteins, termed effector proteins, enable the bacterial pathogens to attach to or damage the host cell). This mechanism is widespread among bacteria, spanning animal and plant pathogens. The corresponding story for eukaryotic pathogens has come to light more recently. We find it pleasing that distantly related eukaryotic pathogens also appear to share a common mechanism─a mechanism that involves eukaryote membrane gymnastics such as secretory vesicles, exocytosis, and endocytosis.

An Update on Space Odyssey, Salmonella Style

Zero gravity. Courtesy of Fabulous
Adventures

A previous post regarding the experiments performed with Salmonella during a Space Shuttle flight elicited some interesting comments. We communicated them to the senior author of the paper, Dr. Cheryl Nickerson of Arizona State University. She sent us the following thoughtful and informative response. We look forward to a flurry of future studies on the effects of space travel on our favorite micro-astronauts.

Circadian Rhythms Revisited (and maybe even explained!)

Synechococcus. Credit: The Lawrence
Berkeley National Laboratory

The very first item in this blog was about the circadian rhythm in cyanobacteria (It Don't Mean a Thing If It Ain't Got That Swing). We celebrated the amazing finding by a group from Nagoya University that the 24-hour circadian clock of Synechococcus elegans can be reconstituted in vitro with just three purified proteins in the presence of ATP. These proteins are kinases that interact with one another, carrying out phosphorylation reactions that exhibit the same periodicity as the whole cell. Mutants with altered clocks also show corresponding changes in vitro.

This group now reports that one of these proteins, the KaiC ATPase, is the timekeeper that is responsible for the characteristic oscillation.