Microbiology
o Systems You can extract the DNA of these symbionts and assemble the whole genome
The genome is a lot smaller, since they dont have to live out in the
environment
Somewhere around 400 kilobase pairs
o These Buchnera endosymbionts are derived from E. coli
We can reconstruct a common ancestor, which would have looked very much
like E. coli
The gene loss must have happened very rapidly
This process is described in a paper by Siv Andersson
After 70 million years, there are no chromosomal rearrangements or gene
acquisitions
But considerable sequence divergence does occur
Theyre changing around 2000 times faster
Accumulation of pseudo-genes restrict the diet of the aphids
The evolutionary dynamic is very different there isnt any rearrangement
Many non-synonymous fewer substitutions occur
Also very few repeats
This sort of genome reduction can get really extreme, as long as the host
relationship is stable enough
The symbiont has lost the ability to regulate its own gene control it doesnt
have the mechanisms that free-living bugs like E. coli have, so it cant make
more or less amino acids depending on the diet that the aphid is on
Another system: Baumannia and Sulcia in the Glassy-winged Shapshooter
o The genomes are pretty similar to Buchnera
o You have to think of the insect like an ecosystem
o One wonders: how much are there similar things going on in out own systems?
o For example, it looks like human genetics determines which bacteria live in our
stomach and intestines, which influences obesity.