Genetics of Bacteria Chapter 8 1

Prokaryotes! Bacteria Bacteriophages Genome Plasmid 2

3 Conjugation, Transformation and Transduction

Bacterial Conjugation Prototrophs survive on “Minimal Media” Auxotrophs have genetic deficiencies 4

5 How Can This Occur?

6 Conjugation = Davis’s U-tube Experiment Two strains of bacteria which have “complementary” deficiencies in their ability to utilize minimal media. Y (Davis knew Y10 and mixed together produced “prototrophic” bacteria) (lacks two genes)(lacks a third gene)

Conjugation F+ and F- Bacteria 7 Conjugation described in this slide does not explain transfer of genes described previously. Davis U-tube But it is a start! 2% GENOME

Conjugation F+ and F- Bacteria 8 Transfer of genes described previously (Davis U-tube) requires the genes on primary chromosome to be transferred.

9 5’ end first

F factor Integration F factor (plasmid) integrates into the genome of F+ 10 Important Note: The blue integrated F-Factor could be reversed 180 degrees (i.e., the origin of transfer would be by “E”)

11 Reversal of F-factor Integration

F’ (“F-Prime”) Formation 12 Plasmid forms from an integrated plasmid and takes some extra genes with it!

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15 Conversion of Hfr to F’ (“F-Prime”)

Copyright © 2010 Pearson Education, Inc. Figure 8-10 part 5

F factor Integration –The Hfr bacteria (F+ to Hfr) F factor (plasmid) integrates into the genome of F+ bacteria rendering them Hfr bacteria High Frequency Recombination Bacteria show higher recombination of genes than say F’ Prime or F+ which might carry a plasmid allele which is also present on main chromosome

Copyright © 2010 Pearson Education, Inc. Figure 8-9 part 2

Copyright © 2010 Pearson Education, Inc. Figure 8-9 part 3 oriT

Copyright © 2010 Pearson Education, Inc. Figure 8-9 part 4

Copyright © 2010 Pearson Education, Inc. Figure 8-9 part 5 Crossing Over can occur; Leftover fragment will degrade

Copyright © 2010 Pearson Education, Inc. Figure 8-9 part 5 Crossing over can occur and residual DNA fragment is degraded.

23 So how do we know the order of gene transfer?

24 HFR Donor were sensitive to Streptomycin and killed. Conjugation was interrupted with blender. Selective Media and Interrupted Conjugation allow minutes for the cell countsto be converted into map units

25 Notice “directionality” of arrows! 5’ 3’ synthesis

Time mapping is performed in a cross involving the genes: his, leu, mal, and xyl. The recipient cells are auxotrophic for all four genes. After 25 minutes, mating is interrupted, with the results in recipient cells shown below. Diagram the positions of these genes on F Factor relative to the OriT (Origin of Transfer) and to one another. a)90% are xyl+ b)80% are mal+ c)20% are his+ d)None are leu+ 26