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Title: Genome-wide selective sweeps and gene-specific sweeps in natural bacterial populations

Multiple models describe the formation and evolution of distinct microbial phylogenetic groups. These evolutionary models make different predictions regarding how adaptive alleles spread through populations and how genetic diversity is maintained. Processes predicted by competing evolutionary models, for example, genome-wide selective sweeps vs gene-specific sweeps, could be captured in natural populations using time-series metagenomics if the approach were applied over a sufficiently long time frame. Direct observations of either process would help resolve how distinct microbial groups evolve. Using a 9-year metagenomic study of a freshwater lake (2005–2013), we explore changes in single-nucleotide polymorphism (SNP) frequencies and patterns of gene gain and loss in 30 bacterial populations. SNP analyses revealed substantial genetic heterogeneity within these populations, although the degree of heterogeneity varied by >1000-fold among populations. SNP allele frequencies also changed dramatically over time within some populations. Interestingly, nearly all SNP variants were slowly purged over several years from one population of green sulfur bacteria, while at the same time multiple genes either swept through or were lost from this population. Furthermore, these patterns were consistent with a genome-wide selective sweep in progress, a process predicted by the ‘ecotype model’ of speciation but not previously observed in nature. In contrast,more » other populations contained large, SNP-free genomic regions that appear to have swept independently through the populations prior to the study without purging diversity elsewhere in the genome. Finally, evidence for both genome-wide and gene-specific sweeps suggests that different models of bacterial speciation may apply to different populations coexisting in the same environment.« less
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  1. USDOE Joint Genome Institute (JGI), Walnut Creek, CA (United States)
  2. Univ. of Wisconsin, Madison, WI (United States). Dept. of Bacteriology
  3. Uppsala Univ. (Sweden). Dept. of Ecology and Genetics
  4. Univ. of Georgia, Athens, GA (United States). Dept. of Marine Sciences
  5. Michigan State Univ., East Lansing, MI (United States). Microbiology and Molecular Genetics
  6. Univ. of Wiscon, Milwaukee, WI (United States). School of Freshwater Sciences
  7. Univ. of Wisconsin, Madison, WI (United States). Dept. of Bacteriology; Univ. of Wisconsin, Madison, WI (United States). Civil and Environmental Engineering
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
The ISME Journal
Additional Journal Information:
Journal Volume: 10; Journal Issue: 7; Journal ID: ISSN 1751-7362
Nature Publishing Group
Research Org:
Dept. of Energy Joint Genome Inst., Walnut Creek, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1379499