APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017;
New Orleans, Louisiana
Session C5: Evolutionary Dynamics of Genomes
2:30 PM–5:18 PM,
Monday, March 13, 2017
Room: 264
Sponsoring
Unit:
DBIO
Chair: Benjamin Greenbaum, Icahn School of Medicine, Mount Sinai
Abstract ID: BAPS.2017.MAR.C5.1
Abstract: C5.00001 : Theory of microbial genome evolution
2:30 PM–3:06 PM
Preview Abstract
Abstract
Author:
Eugene Koonin
(NCBI, NIH)
Bacteria and archaea have small genomes tightly packed with protein-coding
genes. This compactness is commonly perceived as evidence of adaptive genome
streamlining caused by strong purifying selection in large microbial
populations. In such populations, even the small cost incurred by
nonfunctional DNA because of extra energy and time expenditure is thought to
be sufficient for this extra genetic material to be eliminated by selection.
However, contrary to the predictions of this model, there exists a
consistent, positive correlation between the strength of selection at the
protein sequence level, measured as the ratio of nonsynonymous to synonymous
substitution rates, and microbial genome size. By fitting the genome size
distributions in multiple groups of prokaryotes to predictions of
mathematical models of population evolution, we show that only models in
which acquisition of additional genes is, on average, slightly beneficial
yield a good fit to genomic data. Thus, the number of genes in prokaryotic
genomes seems to reflect the equilibrium between the benefit of additional
genes that diminishes as the genome grows and deletion bias. New genes
acquired by microbial genomes, on average, appear to be adaptive. Evolution
of bacterial and archaeal genomes involves extensive horizontal gene
transfer and gene loss. Many microbes have open pangenomes, where each newly
sequenced genome contains more than 10{\%} `ORFans', genes without
detectable homologues in other species. A simple, steady-state evolutionary
model reveals two sharply distinct classes of microbial genes, one of which
(ORFans) is characterized by effectively instantaneous gene replacement,
whereas the other consists of genes with finite, distributed replacement
rates. These findings imply a conservative estimate of at least a billion
distinct genes in the prokaryotic genomic universe.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2017.MAR.C5.1