Small Things Considered

Pictures Considered #42 : Ernst Haeckel's 'Pedigree of Man'

by Christoph Weigel | It's exactly 150 years since the picture considered in this post was published in the 'General Morphology of Organisms' by Ernst Haeckel (1866). "Phylogeny is the evolutionary history of organisms," explains Uwe Hoßfeld, co-author of a recent paper in Nature that celebrates this anniversary. "Because Haeckel was the first actually to define this term, in... Read more →

Pictures Considered #41 : Replica plating

by Elio | In the early stages of modern molecular genetics, say 1942 ‒ 1952, the time came to settle experimentally the old question about whether mutations in bacteria arise spontaneously or are induced by the environment. Call this Mendelian vs. Lamarckian evolution. Read more →

Pictures Considered #40 : The first Continuous Culture Device?

by Elio | In their paper written in 1930, two US Department of Agriculture scientists, L. A. Rogers and E. O. Whittier, probably described the first continuous culture device for bacteria. It had several of the features of what later became known as the chemostat: a growth chamber, a way to deliver fresh nutrient at a set rate, a constant level device (a side tube) to remove spent medium at the same rate as that of addition of fresh medium, and a sampling port. Read more →

Pictures Considered #38 : A Molecular Stiletto

by Christoph Weigel | Imagine you equip your standard E. coli  cells with a few additional genes, conveniently placed on plasmids and under control of inducible promoters. You grow the cells and induce the expression of these additional genes. Not long after, the cytoplasm of the cells turns reddish, when looked at under the fluorescence microscope, due to... Read more →

Pictures Considered #37 : The Queen's Necklaces

by Christoph Weigel | Rod-shaped Escherichia coli cells have, depending on growth conditions, a length of 1 – 2 µm and a diameter of ~0.5 µm but harbor a chromosome that is ~1.5 mm long, a difference in length by a factor of 1,000. So, there is a problem to fit this chromosome into the cell, right? Not so, in fact, because... Read more →

Pictures Considered #36 : The Discovery of Bacterial Minicells

by Elio | Bacterial minicells were first reported in detail in 1967 by a group at the Oak Ridge National Labs led by Howard Adler. The paper had a provocative title: "Miniature Escherichia coli cells deficient in DNA." The authors realized that a mutation was involved and pointed to the fact that the division process appeared to be "normal", if misplaced along the cell. Read more →

Pictures Considered #35 : The Isolation of the Inner and Outer Membrane of E. coli

by Elio | In 1968, Miura and Mizushima published the first report showing that that the inner (cytoplasmic) and outer membrane of E. coli could be separated from one another. The existence of two membranes had been surmised from thin EM sections, but being able to isolate and purify them allowed further studies, especially biochemical ones. Read more →

Pictures Considered #34 : The first look at the two membranes of Gram-negatives

by Elio | In a recent "Classic Spotlight" in the Journal of Bacteriology, the editor in chief, Tom Silhavy, pointed out that the first visual proof that Gram-negative bacteria have two membranes came from work by Bladen and Mergenhagen. In their 1964 paper... Read more →

Pictures Considered #33 : Viral Abundance and Diversity.

by Elio | This picture should hang as a poster in every microbiological lab that is concerned with viruses (and which one isn't, one way or another?). It shows how diverse the viruses that affect hosts of the three domains of life actually are, both in replication strategy and morphology. I confess, ... Read more →

Pictures Considered #32 : A Model for DNA Segregation in 1963.

by Nanne Nanninga | The classic paper on 'The Regulation of DNA Replication in Bacteria' by Jacob et al. (1963) included a model on bacterial DNA segregation. In retrospect the model had far reaching consequences which can still be felt today. It entailed a research program that inspired many scientists. Yet, the model was not the main topic of the paper. Read more →