@article {RN132, title = {Ultrafast Evolution and Loss of CRISPRs Following a Host Shift in a Novel Wildlife Pathogen, Mycoplasma gallisepticum}, journal = {Plos Genetics}, volume = {8}, year = {2012}, type = {Journal Article}, abstract = {
Measureable rates of genome evolution are well documented in human pathogens but are less well understood in bacterial
pathogens in the wild, particularly during and after host switches.
Mycoplasma gallisepticum
(MG) is a pathogenic bacterium
that has evolved predominantly in poultry and recently jumped to wild house finches (
Carpodacus mexicanus
), a common
North American songbird. For the first time we characterize the genome and measure rates of genome evolution in House
Finch isolates of MG, as well as in poultry outgroups. Using whole-genome sequences of 12 House Finch isolates across a
13-year serial sample and an additional four newly sequenced poultry strains, we estimate a nucleotide diversity in House
Finch isolates of only
,
2\% of ancestral poultry strains and a nucleotide substitution rate of 0.8
2
1.2
6
10
2
5
per site per year
both in poultry and in House Finches, an exceptionally fast rate rivaling some of the highest estimates reported thus far for
bacteria. We also found high diversity and complete turnover of CRISPR arrays in poultry MG strains prior to the switch to
the House Finch host, but after the invasion of House Finches there is progressive loss of CRISPR repeat diversity, and
recruitment of novel CRISPR repeats ceases. Recent (2007) House Finch MG strains retain only
,
50\% of the CRISPR
repertoire founding (1994{\textendash}95) strains and have lost the CRISPR{\textendash}associated genes required for CRISPR function. Our results
suggest that genome evolution in bacterial pathogens of wild birds can be extremely rapid and in this case is accompanied

by apparent functional loss of CRISPRs

}, issn = {1553-7390}, doi = {10.1371/journal.pgen.1002511}, url = {http://journals.plos.org/plosgenetics/article/asset?id=10.1371\%2Fjournal.pgen.1002511.PDF}, author = {Delaney, Nigel F. and Balenger, Susan and Bonneaud, Camille and Marx, Christopher J. and Hill, Geoffrey E. and Ferguson-Noel, Naola and Tsai, Peter and Rodrigo, Allen and Edwards, Scott V.} }