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Slide #1. The Boundaries of Bacterial Species Slide #2. Slide #3. Depicting Full Genome Sequences Slide #4. Depicting Full Genome Sequences Slide #5. Inferrring lateral gene transfer (LGT) from <BR>sequence heterogeneity along the chromosome Slide #6. Differences in Base Composition among Bacteria <BR>are Caused by Mutational Biases Slide #7. Strain- & species-specific genes often have ‘atypical’ base compositions Slide #8. Compositional Heterogeneity among Bacterial Genomes Slide #9. Massive gene exchange in microbial genomes Slide #10. Recognizing events of LGT in genomes Slide #11. Mechanisms of Lateral Gene Transfer Slide #12. Consequences of Lateral Gene Transfer Slide #13. Does LGT disrupt bacterial phylogenies? Slide #14. With the potential for LGT of any gene and among all organisms, bacterial species (or other taxonomic groups) might not be definable entities Slide #15. "Gene transfer will obliterate patterns of vertical descent within groups that exchange genes at high frequencies, producing discordant relationships among genes with different ancestries within the same cells" <BR> Gogarten, Doolittle & Lawrence (2002) Prokaryotic evolution in light of gene transfer MBE 19: 2226. Slide #16. (from Zhaxybayeva and Gogarten, 2002) Slide #17. Does LGT result in rampant phylogenetic discordance? Slide #18. A Slide #19. Escherichia Slide #20. Examining phylogenetic disruption Slide #21. Escherichia Slide #22. Interspecies comparisons Slide #23. Frequency of non-resolving alignments Slide #24. II. Two classes of genes in bacterial genomes Slide #25. Why, despite the massive influx of new genes, are appreciable rates of LGT among orthologs only observed within species? Slide #26. Bacterial species are assemblages of lineages that are sufficiently closely related (i.e., > 95% DNA sequence identity in homologs) to potentially exchange any of their shared genes Slide #27. But these genetic / genomic features are being characterized in groups already designated as distinct bacterial species (both E. coli and S. enterica were first recognized in 1885) Slide #28. What is the history of non-conserved portions of the genome? Slide #29. The history of all gene families within the Proteobacteria Slide #30. Results for sporadically distributed genes <BR>(i.e., single copy genes absent from some of the genomes) Slide #31. Figure 3 Slide #32. Does lateral gene transfer catalyze bacterial speciation?