Speaker
Prof.
Sergei Maslov
(Brookhaven National Laboratory)
Description
Understanding evolutionary dynamics of bacterial genomes is
of great importance in microbiology, microbial ecology, and
epidemiology. Collective effects play an important role in
shaping this dynamics due to ubiquitous horizontal gene
transfer between different members of bacterial population.
We recently interpreted the variability of 37 fully
sequenced genomes of E. coli and Shigella strains within a
neutral evolutionary framework and quantified contributions
of random mutations in the clonal frame and homologous
recombination to the observed diversity of the basic genome
of this species. Distinct signatures of spatial SNP
distributions allowed us to separate clonal, and recombined
chromosomal regions when comparing genomes of different
strains. We estimated that in E. coli for every SNP brought
by clonal frame point mutations recombination brings on
average 5-8 SNPs. Our methods also allowed us to estimate
the number of strains frequently exchanging genetic material
with each other to be around 3 x 10^8. This is consistent
with previously published estimates of the effective
population size of E. coli as well as our own analysis of
the MLST data. The observed correlations between SNPs within
recombined regions indicate phage-mediated gene transduction
as the likely mechanism of exchange of genomic segments
between strains. While the vast majority of the basic genome
diversity is consistent with purely neutral model in which
mutations and recombination events are random we also
identified around 30 out of nearly 3900 1kb basic genome
where the observed diversity is significantly higher than
expected this model. Some of these regions contain genes
encoding proteins under positive selection such as
biosynthetic enzymes in the O-antigen region, fimbrial like
adhesins, etc., while other regions have not been studied
before.
Primary author
Prof.
Sergei Maslov
(Brookhaven National Laboratory)
