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

1. How does conjugation work?

Sex in Bacteria

How do bacteria exchange DNA

Fig. 14.9

Fig. 14.11

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 multiplemutations?

How did he get multiple mutations?

What kind of mutations are made by X-rays And what kind by UV light?

What did Lederberg do to get recombinants?

How did Lederberg rule outpossible explanations for hisdata that did not involve exchange ofgenetic information between strains?

eg. Cross feeding (syntropism)

Transformation

After conjugation what are the most common products?

What do the rare classes represent?

Did recombination occur in both directions?

Fig. 14.11

Davis U tube experiment1950

Tatum and Lederberg 1947

Fig. 14.12a

Fig. 14.12b

Fig. 14.13

Fig. 14.14

Fig. 14.15

Fig. 14.16

Fig. 14.17

Is this recombination mechanism equivalent to sexual recombination in eukaryotes?

Three E. coli genomes:K12, UPEC 536 and UPEC CFT073.Blue: core genomeRed: 2 pathogens onlyGreen: 536 onlyOrange: in both pathogens but in different locations

From Brzuszkiewicz et al 2006 PNAS 103, 12879.

Bacterial genomes differin gene content even withinone 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 effectorsIn two genomes of Pseudomonas syringae.

tomato

bean

From Chang et al 2005 PNAS 102, 2549.

DNA exchange in bacteria leadsto development of new niches,

Adaptation to new hosts,Escape from host defense mechanisms