Small Things Considered

Nuclear Option

Photomicrograph of Myrionecta rubra.
Source

Some marine animals─clams, flatworms, and hydras─have green body parts although that is not their true color. Rather, they look green because they have ingested microscopic algae. Inside the animals, the algae act as photosynthetic symbionts, tiny gardens that provide their host with products of their toil. As a variation on this strategy, certain marine predatory ciliates do not bother with the whole prey: they keep the chloroplasts and get rid of most of the rest. This, however, is not a very stable state of affairs because chloroplasts and other organelles (e.g., mitochondria) have transferred many of their genes to the nucleus and, without these genes, do not endure for long.

So, why not steal the nucleus as well?

Talmudic Question #6

With the buzz created by the discovery of giant viruses, e.g., Mimivirus, the distinction between viruses and cells is said to get blurred. I maintain that this is not the case because the single most important distinction is that viruses lose their corporeal integrity, cells do not. What do you think? Are you a blurrer or a non-blurrer?

An aside: Not everyone knows what a "Talmudic Question" is. Rather than telling you what I had in mind, would those who know share their definition?

Ciliate 007

SEM of the ciliate Euplotidium
itoi with bacterial ectosymbionts
on its surface. Courtesy of
Giovanna Rosati.

Certain marine ciliates (i.e., Euplotidium) use devices worthy of James Bond. Or so it looks like. These creatures carry bacterial ectosymbionts belonging to the Verrucomicrobia that have extraordinary attributes. Before revealing what this is about, I need to pause for an admiring gaze at an Euplotidium. What is so startling is that these are single celled organisms with a cellular complexity rivaling that of many a multicellular animal. Legs on a unicellular organism? Actually what look like legs really act like legs. They are bundles of cilia called cirri that permit the organism to walk or crawl on surfaces. Ciliates are like that─remarkable in looks and variety. See where Euplotidium fits in taxonomy.

Back to the bacteria on Euplotidium...

Talmudic Question #5

In a recent essay in Nature, Margaret McFall-Ngai  posits that with regards to intracellular bacteria, “Although widespread among invertebrates, such associations seem to be absent from vertebrates.”  Can you think of an endosymbiont in a vertebrate? (mitochondria don’t count)

Prokaryotes by Any Other Name....

Definitions in biology tend to be elusive because they are often peppered with exceptions. Right now, defining prokaryotes (Bacteria and Archaea, cells without a real nucleus) as being different from eukaryotes (cells with a nucleus) is the subject of a lively discussion. One writer of a piece in Nature (N. Pace) does not believe that the pie of living things should be sliced that way whereas others do (W. Martin and E. V. Koonin). The argument centers on the widely accepted view that prokaryotes come in two kinds, the Bacteria and the Archaea. Because the Archaea have significant similarities with the eukaryotes, it is claimed that the term prokaryote, though cherished by most, is obsolete and misleading and might as well be abandoned...

Bacterial Physiology in Unexpected Places

In a recent Friday New York Times puzzle, the definition for 20 Across was: "Legionella and Listeria" -- 7 letters. Hint: the first two letters are "ae." The answer is half right.

All in the Family

TEM of Candidatus Midchloria mitochindrii inside
a mitochondrion. Source: Luciano Sacchi,
University of Pavia, Italy.

In Spanish or Italian, “colmo” means that something has truly reached the limit, the last straw. For endosymbionts, this can be claimed by bacteria that live not just inside host cells, but within their mitochondria. El colmo! This unusual symbiosis has been found in the cells of the ovaries of the Ixodes ticks that carry Lyme disease. The mitochondria of these cells are quite large and can readily accommodate their guest bacteria. This finding is not entirely new. In the 1970’s, endosymbionts were reported residing in mitochondria, first of ciliates and later of ticks. A recent paper reports the genomic identification of an endomitochondrial bacterium, which turns out to belong to the Rickettsiaceae...