1. How does conjugation work? Sex in Bacteria How do bacteria exchange DNA

Fig. 14.9

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What question did Tatum and Lederberg set out to answer? What led them to expect bacteria exchanged genetic information? Why did he pick the bacteria (E. coli) he used as starting material?

Why did Lederberg want to use multiple mutations? How did he get multiple mutations? What kind of mutations are made by X-rays And what kind by UV light?

B- M- P+ T+ and B+ M+ P- T- culture together Get 10 2 /10 9 prototrophs: B+ M+ P+ T+ What did Lederberg do to get recombinants?

Other possible explanations Cross feeding (syntropism) limiting dilution plating Transformation mixed culture media with each parental type

After conjugation what are the most common products? What do the rare classes represent? Did recombination occur in both directions?

Did all possible parental combinations lead to prototrophs? What must E. coli K12 have for Lederberg’s Experiments to have worked? Why is frequency of prototrophs so low?

Is this recombination mechanism equivalent to sexual recombination in eukaryotes?

Three E. coli genomes: K12, UPEC 536 and UPEC CFT073. Blue: core genome Red: 2 pathogens only Green: 536 only Orange: in both pathogens but in different locations From Brzuszkiewicz et al 2006 PNAS 103, Bacterial genomes differ in gene content even within one species

Whole genome comparisons of bacterial genomes reveal differences in phage content and DNA islands

Plant pathogens differ in content and location of virulence genes. Horizontal transfer is source of Variation for virulence factors Compare location of type III effectors In two genomes of Pseudomonas syringae. tomato bean From Chang et al 2005 PNAS 102, 2549.

Transduction Phage integrate Excise Re-infect and transfer chromosomal DNA between strains

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DNA exchange in bacteria leads to development of new niches, Adaptation to new hosts, Escape from host defense mechanisms