Transcript Lecture 11

Bacterial genetics
• Gram-positive bacteria transform DNA using a
transformasome complex.
Figure 9.1
Gene Transfer by Conjugation
• Conjugation is the transfer of DNA from one
bacterium to another, following cell-to-cell
contact.
- It is typically initiated
by a special pilus
protruding from the
donor cell.
Figure 9.2
Figure 9.3
Figure 9.4
• An integrated F-factor can excise from the
chromosome.
•
- Aberrant excision results in an F′ factor or F′
plasmid, which carries chromosomal genes.
Figure 9.5
Hfr leu+ thr+pro+lac+bio+Sms X
F- leu- thr-pro-lac-bio-SmR
What medium should we use to obtain
1. leu+ transconjugants
2. pro+ transconjugants
3. lac+ transconjugants
Hfr leu+ thr+pro+lac+bio+Sms X
F- leu- thr-pro-lac-bio-SmR
1. leu+ transconjugants
2. pro+ transconjugants
3. lac+ transconjugants
What are the map positions of
leu, pro, and lac?
time No.of colonies on
medium
1
2
3
0
0
0
0
5
0
0
0
10
8
0
0
15
28
6
1
20
48
16
6
25
68
26
11
no.colonies
80
70
60
50
40
30
20
10
0
1
2
3
4
time
5
6
Generalized Transduction
Figure 9.7
Figure 9.9
Figure 9.8
Specialized Transduction
Generalized Recombination
Figure 9.14
Figure 9.15
Figure 9.30
Mobile Genetic Elements
• IS elements transfer by one of 2 mechanisms:
•
- Replicative or nonreplicative transposition
Figure 9.31