Koshlan MeyerBlackwell Naama Pnina Dekel Hopkins Microbiology Course 2010 The BIG question What are the evolutionary consequences of temporarily subjecting Pseudomonas fluorescens ID: 1026259
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1. Experimental EvolutionBen CallahanKoshlan Meyer-BlackwellNaama Pnina DekelHopkins Microbiology Course 2010
2. The BIG question:What are the evolutionary consequences of temporarily subjecting Pseudomonas fluorescens to a challenging chemical environment?Principles:(Chemical) Environment FitnessTradeoffsMicroevolutionary processes
3. The challenge: Nalidixic acidNalidixic 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. Methods2 days20/40/60/80 μg/ml nalidixic acidPseudomonas fluorescens SBW25 LBNalRNalRNalSNalR1/100018 times ~1800 ggyrA-80°C
5. Evolution RespondsNalS-lacz+ NalR ancNalS-lacz+ NalR derNalS-lacz+ NalS ancNalS-lacz+ NalR ancPlating after inoculation and on the next dayAfter 1800 generations of growth in “normal” environment, we evaluate the results:
6. MicroevolutionHow did selection change the (normal) fitness over the experiment?
7. MutationIn E.coli:Yoshida et al. 1998But, In Pseudomonas fluorescens this mutation did not occur in any of the resistant strains. In fact, no mutation in gyrA was found.What mutational paths are available for Nalidixic resistance?Nal resistance
8. MutationIn E.coli:Yoshida et al. 1998But, In Pseudomonas fluorescens this mutation did not occur in any of the resistant strains. In fact, no mutation in gyrA was found.What mutational paths are available for Nalidixic resistance?Nal resistanceThere are multiple paths to Nalidixic acid resistance.
9. TradeoffsHow did Nal resistance impact “normal” fitness? Did [Nal] matter?
10. Tempo and ModeInitial distance from fitness optimum affects the evolutionary “rate”?
11. Tempo and ModeInitial 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. SuggestionsTest lower Nal concentrationsDo tradeoffs change?Evolve in a +Nal broth environmentPresence of Nal alters evolutionary trajectory?
14. SuggestionsTest lower Nal concentrationsDo tradeoffs change?Evolve in a +Nal broth environmentPresence of Nal alters evolutionary trajectory?Thanks!For listening (and transferring… and counting…)