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Reductive genome evolution at both ends of the bacterial population size spectrum

Abstract

Bacterial genomes show substantial variations in size. The smallest bacterial genomes are those of endocellular symbionts of eukaryotic hosts, which have undergone massive genome reduction and show patterns that are consistent with the degenerative processes that are predicted to occur in species with small effective population sizes. However, similar genome reduction is found in some free-living marine cyanobacteria that are characterized by extremely large populations. In this Opinion article, we discuss the different hypotheses that have been proposed to account for this reductive genome evolution at both ends of the bacterial population size spectrum.

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Figure 1: Contrasting relationship between genome size and measures of genetic drift.
Figure 2: Phylogeny, genome statistics and ecological preferences of the Prochlorococcus ecotypes.

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References

  1. McGrath, C. L. & Katz, L. A. Genome diversity in microbial eukaryotes. Trends Ecol. Evol. 19, 32–38 (2004).

    PubMed  Google Scholar 

  2. Lynch, M. The Origins of Genome Architecture. (Sinauer Associates Inc, 2007).

    Google Scholar 

  3. Doolittle, W. F. Is junk DNA bunk? A critique of ENCODE. Proc. Natl Acad. Sci. USA 110, 5294–5300 (2013).

    CAS  PubMed  PubMed Central  Google Scholar 

  4. Giovannoni, S. J. et al. Genome streamlining in a cosmopolitan oceanic bacterium. Science 309, 1242–1245 (2005).

    CAS  PubMed  Google Scholar 

  5. Moran, N. A., McCutcheon, J. P. & Nakabachi, A. Genomics and evolution of heritable bacterial symbionts. Annu. Rev. Genet. 42, 165–190 (2008).

    CAS  PubMed  Google Scholar 

  6. Van Ham, R. C. et al. Reductive genome evolution in Buchnera aphidicola . Proc. Natl Acad. Sci. USA 100, 581–586 (2003).

    CAS  Google Scholar 

  7. Charlesworth, B. Effective population size and patterns of molecular evolution and variation. Nature Rev. Genet. 10, 195–205 (2009).

    CAS  PubMed  Google Scholar 

  8. Lynch, M. & Conery, J. S. The origins of genome complexity. Science 302, 1401–1404 (2003).

    CAS  PubMed  Google Scholar 

  9. Lynch, M. The origins of eukaryotic gene structure. Mol. Biol. Evol. 23, 450–468 (2006).

    CAS  PubMed  Google Scholar 

  10. Lynch, M. Statistical inference on the mechanisms of genome evolution. PLoS Genet. 7, e1001389 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  11. Lynch, M. The evolution of multimeric protein assemblages. Mol. Biol. Evol. 29, 1353–1366 (2012).

    CAS  PubMed  Google Scholar 

  12. Lynch, M. & Abegg, A. The rate of establishment of complex adaptations. Mol. Biol. Evol. 27, 1404–1414 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  13. Koonin, E. V. A non-adaptationist perspective on evolution of genomic complexity or the continued dethroning of man. Cell Cycle 3, 280–285 (2004).

    CAS  PubMed  Google Scholar 

  14. Whitney, K. D., Boussau, B., Baack, E. J. & Garland, T. Drift and genome complexity revisited. PLoS Genet. 7, e1002092 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  15. Whitney, K. D. & Garland, T. Did genetic drift drive increases in genome complexity? PLoS Genet. 6, e1001080 (2010).

    PubMed  PubMed Central  Google Scholar 

  16. Boussau, B., Brown, J. M. & Fujita, M. K. Nonadaptive evolution of mitochondrial genome size. Evolution 65, 2706–2711 (2011).

    PubMed  Google Scholar 

  17. Daubin, V. & Moran, N. A. Comment on 'The origins of genome complexity'. Science 306, 978–978 (2004).

    CAS  PubMed  Google Scholar 

  18. Mira, A. & Moran, N. A. Estimating population size and transmission bottlenecks in maternally transmitted endosymbiotic bacteria. Microb. Ecol. 44, 137–143 (2002).

    CAS  PubMed  Google Scholar 

  19. Toft, C. & Andersson, S. G. E. Evolutionary microbial genomics: insights into bacterial host adaptation. Nature Rev. Genet. 11, 465–475 (2010).

    CAS  PubMed  Google Scholar 

  20. Andersson, S. G. & Kurland, C. G. Reductive evolution of resident genomes. Trends Microbiol. 6, 263–268 (1998).

    CAS  PubMed  Google Scholar 

  21. McCutcheon, J. P. & Moran, N. A. Extreme genome reduction in symbiotic bacteria. Nature Rev. Microbiol. 10, 13–26 (2012).

    CAS  Google Scholar 

  22. Andersson, J. O. & Andersson, S. G. Genome degradation is an ongoing process in Rickettsia. Mol. Biol. Evol. 16, 1178–1191 (1999).

    CAS  PubMed  Google Scholar 

  23. Andersson, G. E., Karlberg, O., Canbäck, B. & Kurland, C. G. On the origin of mitochondria: a genomics perspective. Phil. Trans. R. Soc. Lond. B 358, 165–179 (2003).

    CAS  Google Scholar 

  24. Lynch, M., Koskella, B. & Schaack, S. Mutation pressure and the evolution of organelle genomic architecture. Science 311, 1727–1730 (2006).

    CAS  PubMed  Google Scholar 

  25. Shigenobu, S., Watanabe, H., Hattori, M., Sakaki, Y. & Ishikawa, H. Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp. APS. Nature 407, 81–86 (2000).

    CAS  PubMed  Google Scholar 

  26. Kuo, C.-H., Moran, N. A. & Ochman, H. The consequences of genetic drift for bacterial genome complexity. Genome Res. 19, 1450–1454 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  27. Thompson, C. C. et al. Genomic taxonomy of the genus Prochlorococcus. Microb. Ecol. 66, 752–762 (2013).

    PubMed  Google Scholar 

  28. Partensky, F. & Garczarek, L. Prochlorococcus: advantages and limits of minimalism. Annu. Rev. Mar. Sci. 2, 305–331 (2010).

    Google Scholar 

  29. Giovannoni, S. J., Cameron Thrash, J. & Temperton, B. Implications of streamlining theory for microbial ecology. ISME J. 8, 1553–1565 (2014).

    PubMed  PubMed Central  Google Scholar 

  30. Moran, N. A., McLaughlin, H. J. & Sorek, R. The dynamics and time scale of ongoing genomic erosion in symbiotic bacteria. Science 323, 379–382 (2009).

    CAS  PubMed  Google Scholar 

  31. Moran, N. A. Accelerated evolution and Muller's rachet in endosymbiotic bacteria. Proc. Natl Acad. Sci. USA 93, 2873–2878 (1996).

    CAS  Google Scholar 

  32. Coleman, M. L. et al. Genomic islands and the ecology and evolution of Prochlorococcus. Science 311, 1768–1770 (2006).

    CAS  PubMed  Google Scholar 

  33. Mira, A., Ochman, H. & Moran, N. A. Deletional bias and the evolution of bacterial genomes. Trends Genet. 17, 589–596 (2001).

    CAS  PubMed  Google Scholar 

  34. Kuo, C.-H. & Ochman, H. Deletional bias across the three domains of life. Genome Biol. Evol. 1, 145–152 (2009).

    PubMed  PubMed Central  Google Scholar 

  35. Pérez-Brocal, V. et al. A small microbial genome: the end of a long symbiotic relationship? Science 314, 312–313 (2006).

    PubMed  Google Scholar 

  36. Wernegreen, J. J. Genome evolution in bacterial endosymbionts of insects. Nature Rev. Genet. 3, 850–861 (2002).

    CAS  PubMed  Google Scholar 

  37. Tamas, I. et al. 50 million years of genomic stasis in endosymbiotic bacteria. Science 296, 2376–2379 (2002).

    CAS  PubMed  Google Scholar 

  38. Dufresne, A. et al. Genome sequence of the cyanobacterium Prochlorococcus marinus SS120, a nearly minimal oxyphototrophic genome. Proc. Natl Acad. Sci. USA 100, 10020–10025 (2003).

    CAS  Google Scholar 

  39. Dufresne, A., Garczarek, L. & Partensky, F. Accelerated evolution associated with genome reduction in a free-living prokaryote. Genome Biol. 6, 1–10 (2005).

    Google Scholar 

  40. Rocap, G. et al. Genome divergence in two Prochlorococcus ecotypes reflects oceanic niche differentiation. Nature 424, 1042–1047 (2003).

    CAS  PubMed  Google Scholar 

  41. Paul, S., Dutta, A., Bag, S. K., Das, S. & Dutta, C. Distinct, ecotype-specific genome and proteome signatures in the marine cyanobacteria Prochlorococcus. BMC Genomics 11, 103 (2010).

    PubMed  PubMed Central  Google Scholar 

  42. Sullivan, M. B., Waterbury, J. B. & Chisholm, S. W. Cyanophages infecting the oceanic cyanobacterium Prochlorococcus. Nature 424, 1047–1051 (2003).

    CAS  PubMed  Google Scholar 

  43. Sullivan, M. B., Coleman, M. L., Weigele, P., Rohwer, F. & Chisholm, S. W. Three Prochlorococcus cyanophage genomes: signature features and ecological interpretations. PLoS Biol. 3, e144 (2005).

    PubMed  PubMed Central  Google Scholar 

  44. Kettler, G. C. et al. Patterns and implications of gene gain and loss in the evolution of Prochlorococcus. Plos Genet. 3, e231 (2007).

    PubMed  PubMed Central  Google Scholar 

  45. Luo, H., Friedman, R., Tang, J. & Hughes, A. L. Genome reduction by deletion of paralogs in the marine cyanobacterium Prochlorococcus. Mol. Biol. Evol. 28, 2751–2760 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  46. Clark, M. A., Moran, N. A. & Baumann, P. Sequence evolution in bacterial endosymbionts having extreme base compositions. Mol. Biol. Evol. 16, 1586–1598 (1999).

    CAS  PubMed  Google Scholar 

  47. Hu, J. & Blanchard, J. L. Environmental sequence data from the Sargasso Sea reveal that the characteristics of genome reduction in Prochlorococcus are not a harbinger for an escalation in genetic drift. Mol. Biol. Evol. 26, 5–13 (2009).

    PubMed  Google Scholar 

  48. Sun, Z. & Blanchard, J. L. Strong genome-wide selection early in the evolution of Prochlorococcus resulted in a reduced genome through the loss of a large number of small effect genes. PLoS ONE 9, e88837 (2014).

    PubMed  PubMed Central  Google Scholar 

  49. Wernegreen, J. J. & Moran, N. A. Evidence for genetic drift in endosymbionts (Buchnera): analyses of protein-coding genes. Mol. Biol. Evol. 16, 83–97 (1999).

    CAS  PubMed  Google Scholar 

  50. Felsenstein, J. Theoretical Evolutionary Genetics. (Univ. of Washington, 2005).

    Google Scholar 

  51. Muller, H. J. The relation of recombination to mutational advance. Mutat. Res. 1, 2–9 (1964).

    Google Scholar 

  52. Degnan, P. H., Ochman, H. & Moran, N. A. Sequence conservation and functional constraint on intergenic spacers in reduced genomes of the obligate symbiont Buchnera. PLoS Genet. 7, e1002252 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  53. Flombaum, P. et al. Present and future global distributions of the marine Cyanobacteria Prochlorococcus and Synechococcus . Proc. Natl Acad. Sci. USA 110, 9824–9829 (2013).

    CAS  Google Scholar 

  54. Baumdicker, F., Hess, W. R. & Pfaffelhuber, P. The infinitely many genes model for the distributed genome of bacteria. Genome Biol. Evol. 4, 443–456 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  55. Charlesworth, J. & Eyre-Walker, A. The rate of adaptive evolution in enteric bacteria. Mol. Biol. Evol. 23, 1348–1356 (2006).

    CAS  PubMed  Google Scholar 

  56. Kashtan, N. et al. Single-cell genomics reveals hundreds of coexisting subpopulations in wild Prochlorococcus. Science 344, 416–420 (2014).

    CAS  PubMed  Google Scholar 

  57. Zhaxybayeva, O., Doolittle, W. F., Papke, R. T. & Gogarten, J. P. Intertwined evolutionary histories of marine Synechococcus and Prochlorococcus marinus. Genome Biol. Evol. 1, 325–339 (2009).

    PubMed  PubMed Central  Google Scholar 

  58. Marais, G. A. B., Calteau, A. & Tenaillon, O. Mutation rate and genome reduction in endosymbiotic and free-living bacteria. Genetica 134, 205–210 (2008).

    PubMed  Google Scholar 

  59. Viklund, J., Ettema, T. J. G. & Andersson, S. G. E. Independent genome reduction and phylogenetic reclassification of the oceanic SAR11 clade. Mol. Biol. Evol. 29, 599–615 (2012).

    CAS  PubMed  Google Scholar 

  60. Rocha, E. P. & Danchin, A. Base composition bias might result from competition for metabolic resources. Trends Genet. 18, 291–294 (2002).

    CAS  PubMed  Google Scholar 

  61. Coleman, M. L. & Chisholm, S. W. Ecosystem-specific selection pressures revealed through comparative population genomics. Proc. Natl Acad. Sci. USA 107, 18634–18639 (2010).

    CAS  Google Scholar 

  62. Mary, I., Tu, C.-J., Grossman, A. & Vaulot, D. Effects of high light on transcripts of stress-associated genes for the cyanobacteria Synechocystis sp. PCC 6803 and Prochlorococcus MED4 and MIT9313. Microbiology 150, 1271–1281 (2004).

    CAS  PubMed  Google Scholar 

  63. Morris, J. J., Lenski, R. E. & Zinser, E. R. The Black Queen hypothesis: evolution of dependencies through adaptive gene loss. mBio 3, e00036–12 (2012).

    PubMed  PubMed Central  Google Scholar 

  64. Taddei, F. et al. Role of mutator alleles in adaptive evolution. Nature 387, 700–702 (1997).

    CAS  PubMed  Google Scholar 

  65. Tenaillon, O., Toupance, B., Nagard, H. L., Taddei, F. & Godelle, B. Mutators, population size, adaptive landscape and the adaptation of asexual populations of bacteria. Genetics 152, 485–493 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  66. Denamur, E. et al. Evolutionary implications of the frequent horizontal transfer of mismatch repair genes. Cell 103, 711–721 (2000).

    CAS  PubMed  Google Scholar 

  67. Osburne, M. S., Holmbeck, B. M., Coe, A. & Chisholm, S. W. The spontaneous mutation frequencies of Prochlorococcus strains are commensurate with those of other bacteria. Environ. Microbiol. Rep. 3, 744–749 (2011).

    CAS  PubMed  Google Scholar 

  68. Kissling, G. E., Grogan, D. W. & Drake, J. W. Confounders of mutation-rate estimators: selection and phenotypic lag in Thermus thermophilus. Mut. Res. Fundam. Mol. Mech. Mutag. 749, 16–20 (2013).

    CAS  Google Scholar 

  69. Lynch, M., Bobay, L.-M., Catania, F., Gout, J.-F. & Rho, M. The repatterning of eukaryotic genomes by random genetic drift. Annu. Rev. Genom. Hum. Genet. 12, 347–366 (2011).

    CAS  Google Scholar 

  70. Yu, T. et al. Codon usage patterns and adaptive evolution of marine unicellular cyanobacteria Synechococcus and Prochlorococcus. Mol. Phylogenet. Evol. 62, 206–213 (2012).

    PubMed  Google Scholar 

  71. Hansen, A. K. & Moran, N. A. Altered tRNA characteristics and 3′ maturation in bacterial symbionts with reduced genomes. Nucleic Acids Res. 40, 7870–7884 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  72. Abbot, P. & Moran, N. A. Extremely low levels of genetic polymorphism in endosymbionts (Buchnera) of aphids (Pemphigus). Mol. Ecol. 11, 2649–2660 (2002).

    CAS  PubMed  Google Scholar 

  73. Zhao, F. & Qin, S. Comparative molecular population genetics of phycoerythrin locus in Prochlorococcus. Genetica 129, 291–299 (2007).

    CAS  PubMed  Google Scholar 

  74. Scanlan, D. J., Hess, W. R., Partensky, F., Newman, J. & Vaulot, D. High degree of genetic variation in Prochlorococcus (Prochlorophyta) revealed by RFLP analysis. Eur. J. Phycol. 31, 1–9 (1996).

    Google Scholar 

  75. Jameson, E., Joint, I., Mann, N. H. & Mühling, M. Application of a novel rpoC1-RFLP approach reveals that marine Prochlorococcus populations in the atlantic gyres are composed of greater microdiversity than previously described. Microb. Ecol. 55, 141–151 (2008).

    PubMed  Google Scholar 

  76. Partensky, F., Hess, W. R. & Vaulot, D. Prochlorococcus, a marine photosynthetic prokaryote of global significance. Microbiol. Mol. Biol. Rev. 63, 106–127 (1999).

    CAS  PubMed  PubMed Central  Google Scholar 

  77. Pedrós-Alió, C. The rare bacterial biosphere. Annu. Rev. Mar. Sci. 4, 449–466 (2012).

    Google Scholar 

  78. Ohta, T. Fixation probability of a mutant influenced by random fluctuation of selection intensity. Genet. Res. 19, 33–38 (1972).

    Google Scholar 

  79. Yang, Z. PAML 4: phylogenetic analysis by maximum likelihood. Mol. Biol. Evol. 24, 1586–1591 (2007).

    CAS  PubMed  Google Scholar 

  80. Dutheil, J. & Boussau, B. Non-homogeneous models of sequence evolution in the Bio++ suite of libraries and programs. BMC Evol. Biol. 8, 255 (2008).

    PubMed  PubMed Central  Google Scholar 

  81. Guéguen, L. et al. Bio++: efficient extensible libraries and tools for computational molecular evolution. Mol. Biol. Evol. 30, 1745–1750 (2013).

    PubMed  Google Scholar 

  82. Nielsen, R., DuMont, V. L. B., Hubisz, M. J. & Aquadro, C. F. Maximum likelihood estimation of ancestral codon usage bias parameters in Drosophila. Mol. Biol. Evol. 24, 228–235 (2007).

    CAS  PubMed  Google Scholar 

  83. Rispe, C. & Moran, N. A. Accumulation of deleterious mutations in endosymbionts: Muller's ratchet with two levels of selection. Am. Nat. 156, 425–441 (2000).

    PubMed  Google Scholar 

  84. Pettersson, M. E. & Berg, O. G. Muller's ratchet in symbiont populations. Genetica 130, 199–211 (2007).

    PubMed  Google Scholar 

  85. O'Fallon, B. Population structure, levels of selection, and the evolution of intracellular symbionts. Evolution 62, 361–373 (2008).

    PubMed  Google Scholar 

  86. Eigen, M. Selforganization of matter and the evolution of biological macromolecules. Naturwissenschaften 58, 465–523 (1971).

    CAS  PubMed  Google Scholar 

  87. Takeuchi, N. & Hogeweg, P. Error-threshold exists in fitness landscapes with lethal mutants. BMC Evol. Biol. 7, 15 (2007).

    PubMed  PubMed Central  Google Scholar 

  88. Francis, A. R. & Tanaka, M. M. Evolution of variation in presence and absence of genes in bacterial pathways. BMC Evol. Biol. 12, 55 (2012).

    PubMed  PubMed Central  Google Scholar 

  89. De Boer, F. K. & Hogeweg, P. Eco-evolutionary dynamics, coding structure and the information threshold. BMC Evol. Biol. 10, 361 (2010).

    PubMed  PubMed Central  Google Scholar 

  90. Knibbe, C., Coulon, A., Mazet, O., Fayard, J.-M. & Beslon, G. A. Long-term evolutionary pressure on the amount of noncoding DNA. Mol. Biol. Evol. 24, 2344–2353 (2007).

    CAS  PubMed  Google Scholar 

  91. Wagner, A. Redundant gene functions and natural selection. J. Evol. Biol. 12, 1–16 (1999).

    Google Scholar 

  92. Cuypers, T. D. & Hogeweg, P. Virtual genomes in flux: an interplay of neutrality and adaptability explains genome expansion and streamlining. Genome Biol. Evol. 4, 212–229 (2012).

    PubMed  PubMed Central  Google Scholar 

  93. Lynch, M. Streamlining and simplification of microbial genome architecture. Annu. Rev. Microbiol. 60, 327–349 (2006).

    CAS  PubMed  Google Scholar 

  94. Urbach, E., Scanlan, D. J., Distel, D. L., Waterbury, J. B. & Chisholm, S. W. Rapid diversification of marine picophytoplankton with dissimilar light-harvesting structures inferred from sequences of Prochlorococcus and Synechococcus (Cyanobacteria). J. Mol. Evol. 46, 188–201 (1998).

    CAS  PubMed  Google Scholar 

  95. Guindon, S. et al. New algorithms and methods to estimate maximum-likelihood phylogenies: assessing the performance of PhyML 3.0. Syst. Biol. 59, 307–321 (2010).

    CAS  PubMed  Google Scholar 

  96. Penel, S. et al. Databases of homologous gene families for comparative genomics. BMC Bioinformatics 10, S3 (2009).

    PubMed  PubMed Central  Google Scholar 

  97. Löytynoja, A. & Goldman, N. An algorithm for progressive multiple alignment of sequences with insertions. Proc. Natl Acad. Sci. USA 102, 10557–10562 (2005).

    Google Scholar 

  98. García-Fernández, J. M., de Marsac, N. T. & Diez, J. Streamlined regulation and gene loss as adaptive mechanisms in Prochlorococcus for optimized nitrogen utilization in oligotrophic environments. Microbiol. Mol. Biol. Rev. 68, 630–638 (2004).

    PubMed  PubMed Central  Google Scholar 

  99. Itoh, T., Martin, W. & Nei, M. Acceleration of genomic evolution caused by enhanced mutation rate in endocellular symbionts. Proc. Natl Acad. Sci. USA 99, 12944–12948 (2002).

    CAS  PubMed  PubMed Central  Google Scholar 

  100. Avrani, S., Wurtzel, O., Sharon, I., Sorek, R. & Lindell, D. Genomic island variability facilitates Prochlorococcus–virus coexistence. Nature 474, 604–608 (2011).

    CAS  PubMed  Google Scholar 

  101. Scanlan, D. J. et al. Ecological genomics of marine picocyanobacteria. Microbiol. Mol. Biol. Rev. 73, 249–299 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

B.B. thanks the French Research Ministry for Ph.D. funding. This research was funded by the Centre National de la Recherche Scientifique (interdisciplinary programmes PEPS and PEPII) and the French National Research Agency from grant ANR-10-BINF-01-01.

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Correspondence to Vincent Daubin.

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PowerPoint slides

Glossary

Codon usage bias

The frequency of occurrence of synonymous codons in a coding sequence.

Effective population size

(Ne). The size of an ideal population that has the same level of genetic diversity as a real population; it is used to mathematically model genetic drift.

Endosymbiotic

A term used to describe an organism that lives within another organism.

Error threshold

A process that limits the amount of information that a genome can store at a given mutation rate.

Genetic drift

A change of allele frequencies owing to effects of random sampling from parents to progeny in a finite population.

Genome streamlining

A selective process that drives genome reduction by the elimination of the genes that make the lowest contribution to fitness.

Ka/Ks

(Also known as dN/dS). The ratio between the rate of non-synonymous substitutions (that is, amino acid replacements) and the rate of synonymous substitutions (that is, changes among the synonymous codons of an amino acid).

Muller's ratchet

A process that affects small asexual populations, in which deleterious substitutions tend to accumulate over time.

Mutators

Individuals that have a higher mutation rate than the species-average mutation rate.

Polymorphism

A difference in DNA sequence among individuals of the same species.

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Batut, B., Knibbe, C., Marais, G. et al. Reductive genome evolution at both ends of the bacterial population size spectrum. Nat Rev Microbiol 12, 841–850 (2014). https://doi.org/10.1038/nrmicro3331

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