Download Bacterial and Viral Genetic Systems

Cholera bacteria
H. pylori
Bacterial and Viral Genetic
Systems
Part I
Ch. 8
Ebola virus
Outline
• Techniques to study bacteria
• The bacterial genome
• Plasmids
• Gene Transfer
• Mapping bacterial genes
• Antibiotic resistance
• Bacterial transformation
Bacterial “in vitro” growth
Liquid
OR
solid agar plates
You will do in lab next week
Bacterial Growth
• Minimal Growth Media
• For prototrophs
• Complete Growth Media
• For auxtrophs (mutants)
Bacterial Colony
Colonies are “clones”
Mutant bacteria: can be found based on their “food” requirements
Bacterial Genome
(normally—there are exceptions)
• A circular chromosome
• Haploid
• Normally compact DNA
• NO nuclear membrane: prokaryote—no exception to this rule
DNA “escaping” out of damaged cell
Bacterial Plasmids
1. What are they?
2. What affect can they have on the bacterial cell?
3. How did they get inside the cell?
2 plasmids joined togeth
Some plasmids are integrated
And some remain independent.
Episomes can be either!
Episome
• The fertility factor (F factor) is an episome
• Controls gene exchange and mating in bacteria
Methods for bacterial gene transfer
(in nature)
• Conjugation
• Transformation
You will do this in the lab!
• Transduction
Methods for bacterial gene transfer (in nature)
DNA transfer is not linked to
reproduction in bacteria.
• Conjugation: bacteria to bacteria
• Transformation: external environment to bug (bacteria)
• Transduction: from virus to bug!
Methods for bacterial gene transfer
(in nature)
• Conjugation: often involves recombination
• Transformation: May have recombination
• Transduction: May have recombination
How do we know?
Experimental evidence to support bacterial
recombination
MINIMAL MEDIA
MIX STRAINS
SOME GROWTH
NO GROWTH ON EITHER PLATE
Most conjugation transfers requires
the “F” factor
Sex pilus
Bacterial Recombination
• Certain bacterial cells show recombination with “F” factor
• These are called High-frequency (Hfr) cells
Hfr cells and stepwise recombination
Hfr cell to a F’ cell
• The F factor is cut from the bacterial chromosme and
may even carry some bacterial chromosome with it!
Partial diploids
• F’ can conjugate with F- cell.
• Leads to “partial diploid”= merozygotes
• Two copies of some genes
Mapping bacterial genes
• Using “interrupted conjugation
Transfer times indicate map
distances
0
origin
10
5
azi
ton
15
20
lac
25
gal
R Plasmids
• Contain genes for
antibiotic resistance
• Easily spread among
unrelated bacteria
Fish bacteria
E. coli
E. coli
Transformation
• Uptake of DNA by bacteria from its external environment
• May be DNA fragment
• Bacterial cell must be “competent”
• May recombine with host’s DNA
TRANSFORMANTS
Transformation can be also used to map
bacterial genes
Note:
• You will carry out a bacterial
transformation in lab next week;
however, there will be some technical
differences from what may occur in
nature.
• I will emphasize these in lab.
• Next we complete chapter 8
– Viral genetic systems