Purple balloons and the secret of life: Génome at Genève

Lucky me, I am enjoying a few weeks with my partner in Geneva, Switzerland. During one of our first walks around the city, we noticed a big purple balloon on a small island in the Rhone river. Once we got closer (there is a bridge, no need to swim), we realized that this was no balloon --but a giant cell nucleus.

The bright purple dome, 14 meters in diameter, hosts an exhibition entitled Génome: voyage au coeur du vivant (Genome: a journey to the centre of life), or The secret of life (this subtitle appears on the English-version booklet).

Inside the dome --the cell nucleus-- we enjoyed a multifaceted, imaginative and colourful (even psychedelic?) introduction to genetics and the human genome: from Rosalind Franklin to genome sequencing, from DNA replication to dimples. But let me quote from the first page of the booklet, where the purpose of the exhibition is clearly described:

Dear VISITOR

We would like to take a minute
of your time to explain that

AN EXHIBITION IS FICTION

The wonderful world of the genome, which you will discover here, is an interpretation of reality. A purely scientific explanation could be difficult to understand. On the other hand an over-simplified one would not do justice to the astonishing ingenuity of nature.

You are about to enter a complex universe which is invisible to the naked eye. By using comparison and metaphor, a touch of poetry and humour, we hope that you will be both entertained and informed.


Please remember this message because it is true of all exhibitions; they are all interpretations of reality to a greater or lesser degree.

What an excellent description of what science communication to the general public should be! A delicate balance between (boring?) scientific information and (useless?) entertaining.

Did the Génome organizers accomplished their purpose? Well, they did it for us. You still have till February 28th to judge for yourself but, if you cannot make it to Geneva in time, the following video may give you a vague indication of what's going on inside the purple nucleus:



Génome: voyage au coeur du vivant has something for everyone. Science geeks may especially enjoy the awesome animations created by Drew Berry (including the one projected on the 360-degree screen over our heads!). Perhaps the name of this biologist and animator from the Walter & Eliza Hall Institute of Biomedical Research, Australia, does not ring a bell with you. But I'm almost certain that you have seen some of his award-winning films. See, for instance, the following selection:



The Génome booklet ends with some interesting "food for thought":

Perhaps we should take a philosophical view and agree that, in order to live life to the full, we humans will always need uncertainty!

Well put. And this goes far beyond genetics and evolution...



Links:
- Génome: voyage au coeur du vivant, exhibition webpage (in French), Université de Genève. It contains videos, photos and additional information.
- Genome: a journey to the centre of life, Swiss National Science Foundation.
- WEHI-TV, where you can watch and download several animations created at the Walter & Eliza Hall Institute of Biomedical Research, Australia. Titles include: Body Code, Immunology, Malaria Lifecycle.
- YouTube channel of the Walter & Eliza Hall Institute.
- Drew Berry, biomedical animator, CGSociety (Society of Digital Artists).
- An interview with Drew Berry at SeedMagazine.com

Image credits:
Festival Arbres & Lumières Geneva 2009. Île Rousseau with the Genome exhibition dome. Photo by Alejandro Pérez.

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Size and shape in the genomes of actinomycetes

A new genome sequence of an antibiotic-producing actinomycete has been recently published in Nature Biotechnology. This seems to me a good excuse to highlight some peculiar aspects of genome evolution in this group of bacteria.

The mentioned microorganism is Saccharopolyspora erythraea, known as an industrial source for erythromycin. The size of the genome, 8.2 Mbp (Mbp = megabasepairs = million base pairs), is similar to that of Streptomyces coelicolor (8.7 Mbp) and Streptomyces avermitilis (9 Mbp). These are some of the largest genomes in bacteria, although much smaller genomes are found in other actinomycetes. An example of the latter is Bifidobacterium adolescentis, with only 2.1 Mbp (not to mention the obligate parasite Tropheryma whipplei, the causative agent of Whipple's disease, with a tiny 0.9-Mbp genome).

In the Sac. erythraea chromosome, the majority of conserved, essential genes are contained in a region extending either side of the origin of replication (the "core"). This genome organization consisting of core and "non-core" regions is also found in streptomycetes. The non-core region (3.8 Mbp in Sac. erythraea) includes most of the genes coding for conditionally adaptive functions, such as production of secondary metabolites (although the genes for erythromycin synthesis happen to be located in the core).

What about shape? Most bacteria possess a circular chromosome, which is the case of Sac. erythraea and the majority of actinomycetes. On the other hand, at least some species of Streptomyces and Rhodococcus contain linear chromosomes. Given that actinomycetes more closely related to Rhodococcus (such as Nocardia) possess circular chromosomes, linearization may have occurred more than once during the evolution of this group of bacteria. Remarkably, genomic instability is frequently found in Streptomyces: the non-core region of the chromosome contains transposable elements and is prone to undergo rearrangements and deletions. This leads to large-scale variations, even among genomes of the same species. When the telomeres are lost, a circular chromosome results, and there are examples of the co-existence of linear and circular forms for a particular strain. It has been proposed that linear chromosomes arose from the recombination of linear plasmids with circular chromosomes, and that linear plasmids evolved from bacteriophages.

(Figure: Schematic representation of Saccharopolyspora erythraea chromosome. Reprinted by permission from Macmillan Publishers Ltd: Nat. Biotechnol. 25: 447-453, copyright 2007).

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