Tag: symbioses

World’s Smallest Genome of a Cellular Organism?

ResearchBlogging.org

A one page paper in Science reports on what I think is one of the most exciting findings in microbial genomics in years. The reports describes the sequencing and analysis of the genome of a bacterial endosymbiont of an aphid. This bacteria, known as Carsonella, has a TINY genome – only 160 kbp in length. This is ~ 3 fold smaller than the previously known smallest genome – that of Nanoarchaeum equitans which has a genome of 490 kbp.

I think almost certainly this symbiont should be considered an organelle. It is missing many cellular functions found even in the most reduced symbionts. Thus in essence it may not be the smallest genome of a cellular organism. But who cares how we define it. If it is a new organelle – that is amazing. If it is a tiny cellular genome – that is amazing too.

One thing that strikes me as strange is the fact that the paper is only one page long. It contains so little detail on what was done and what was found in the genome that the story is woefully incomplete. This I would guess is somehow related to a rush to publish but also likely due to it being published in Science, which has severe page restrictions.

This paper has been getting ENORMOUS press coverage for valid reasons. But I agree with Craig Venter (see the New Scientist article) that this genome is not of much relevance to efforts to create a “minimal” genome. This is because the ideal minimal genome is one that can support independent life. Carsonella, is far from independent and thus represents a really wild evolutionary story, but nothing of much relevance to minimal genome studies.

Some related links:

Nakabachi, A., Yamashita, A., Toh, H., Ishikawa, H., Dunbar, H., Moran, N., & Hattori, M. (2006). The 160-Kilobase Genome of the Bacterial Endosymbiont Carsonella Science, 314 (5797), 267-267 DOI: 10.1126/science.1134196

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This is from the “Tree of Life Blog”
of Jonathan Eisen, an evolutionary biologist and Open Access advocate
at the University of California, Davis. For short updates, follow me on Twitter.

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Open Access Biology highlights – The Intriguing Life of Endosymbionts

Two new articles published in the last issue of PLoS Biology bring forth some wildly interesting details about the lives of endosymbiotic bacteria.

One of the articles is about the role Wolbachia may play in speciation in Drosophila species. Wolbachia are a type of bacteira that are found to infect a wide diversity of invertebrate species. These bacteria are transmitted directly from mother to offspring much like mitochondria. Interestingly, many have evolved specialized means of negatively impacting male offspring. In the PLoS Biology study, the researchers were working on a type of Wolbachia known to cause cytoplasmic incompatability in which infected male offspring cannot produce offspring with uninfected females. Since these males can produce offspring with infected females, this helps contribute to the spread of the Wolbachia in the population. To make a long story short, the current paper proposes that not only can Wolbachia apparently lead to speciation through behavioral affects on the host, but that these affects can be stimulated even in species not infected by Wolbachia, if another similar species in the same area is infected. To learn more about the study read the synopsis here. I am personally interested in this story because we published the first Wolbachia genome a few years ago in PLoS Biology.

The second story to me is even more interesting. This relates to a bacterial symbiont that is found in the gut of a stinkbug species. The paper is important because the symbiont in this case does not live inside the cells of its host as do many other gut symbionts of insects. Instead, the symbiont lives in an extracellular capsule. Interestingly, the symbiont is transmitted to offspring not directly in eggs as in many other symbionts, but indirectly. The mother deposits a mass of the bacteria near the eggs and these are then consumed by the young just after hatching (the video of this is amazing).

The paper shows that these symbionts possess many of the genomic features found in other transmissable symbionts – including small genomes, high AT contents, and high rates of evolution (you can read more about this in my recent paper on symbionts of the glassy winged sharpshooter here or in my earlier blog). Many previously thought that these genomic features were related to the intracellular lifestyle of symbionts. But given that the same features are found in these extracellular symbionts, this suggests that the shared genome features are probably related to experiencing population bottlenecks in transmission from mother to offspring. See the synopsis of the paper here.

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This is from the “Tree of Life Blog”
of Jonathan Eisen, an evolutionary biologist and Open Access advocate
at the University of California, Davis. For short updates, follow me on Twitter.

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Glassy winged sharpshooter symbionts

ResearchBlogging.org

For those interested in wine production, or symbioses, you maybe interested in a paper we published a few days ago. It was on a study we did of bacterial symbionts of an insect known as the glassy winged sharpshooter. This insect is a vector for Pierce’s Disease in grapes – a nasty disease that if it is found in a vineyard might lead to the vineyard being sacrificed for the greater good.

Anyway – we did a study of bacteria that live inside the insect that make nutrients for their insect host and without whcih the insect will die. An understanding of these symbionts will hopefully lead to better methods to control the spread of this invasive insect.

Our paper can be found in PLoS Biology here.
A synopsis of our article is here.
An article in Science Now about our study is here
An article in the Central Valley Business Times is here.
Nature highlighted it in their “Research highlights” section
And ASM article about this here
Link to our collaborator’s lab (Nancy Moran)

Some new links about our paper

For more information about the sharpshooter and Pierce’s Disease seee the following links

  • Pierce’s Disease Control Program for State of California: here
  • Glassy winged sharpshooter media information here
  • Introduction to Pierce’s Disease here

Wu, D., Daugherty, S., Van Aken, S., Pai, G., Watkins, K., Khouri, H., Tallon, L., Zaborsky, J., Dunbar, H., Tran, P., Moran, N., & Eisen, J. (2006). Metabolic Complementarity and Genomics of the Dual Bacterial Symbiosis of Sharpshooters PLoS Biology, 4 (6) DOI: 10.1371/journal.pbio.0040188

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This is from the “Tree of Life Blog”
of Jonathan Eisen, an evolutionary biologist and Open Access advocate
at the University of California, Davis. For short updates, follow me on Twitter.

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