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Experimental Evolution

Hopkins Microbiology Course 2010. Experimental Evolution. Ben Callahan Koshlan Meyer-Blackwell Naama Pnina Dekel. The BIG question:. Principles:. (Chemical) Environment Fitness Tradeoffs Microevolutionary processes.

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Experimental Evolution

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  1. Hopkins Microbiology Course 2010 Experimental Evolution Ben Callahan Koshlan Meyer-Blackwell NaamaPninaDekel

  2. The BIG question: Principles: • (Chemical) Environment Fitness • Tradeoffs • Microevolutionary processes • What are the evolutionary consequences of temporarily subjecting Pseudomonas fluorescensto a challenging chemical environment?

  3. The challenge: Nalidixic acid Nalidixic acid interferes with the ability of DNA gyrase to “nick” the DNA. This “nicking” is necessary to relieve super-coiling which prevents DNA replication from proceeding.

  4. Methods NalR NalS 1/1000 2 days 18 times ~1800 g NalR 20/40/60/80 μg/ml nalidixic acid LB Pseudomonas fluorescens SBW25 gyrA -80°C NalR

  5. Evolution Responds After 1800 generations of growth in “normal” environment, we evaluate the results: NalS-lacz+ NalSanc NalS-lacz+ NalRanc NalS-lacz+ NalRanc NalS-lacz+ NalRder Plating after inoculation and on the next day

  6. Microevolution How did selection change the (normal) fitness over the experiment?

  7. Mutation What mutational paths are available for Nalidixic resistance? Nal resistance In E.coli: Yoshida et al. 1998 But, In Pseudomonas fluorescensthis mutation did not occur in any of the resistant strains. In fact, no mutation in gyrA was found.

  8. Mutation What mutational paths are available for Nalidixic resistance? Nal resistance In E.coli: Yoshida et al. 1998 But, In Pseudomonas fluorescensthis mutation did not occur in any of the resistant strains. In fact, no mutation in gyrA was found. There are multiple paths to Nalidixic acid resistance.

  9. Tradeoffs How did Nal resistance impact “normal” fitness? Did [Nal] matter?

  10. Tempo and Mode Initial distance from fitness optimum affects the evolutionary “rate”?

  11. Tempo and Mode Initial distance from fitness optimum affects the evolutionary “rate”? Nal resistance never reverted!

  12. Fitness landscape is multidimensional Multiple paths to Nal resistance. Multiple “fixes” for Nal-resistance tradeoffs.

  13. Suggestions • Test lower Nal concentrations • Do tradeoffs change? • Evolve in a +Nal broth environment • Presence of Nal alters evolutionary trajectory?

  14. Suggestions • Test lower Nal concentrations • Do tradeoffs change? • Evolve in a +Nal broth environment • Presence of Nal alters evolutionary trajectory? Thanks! For listening (and transferring… and counting…)

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