Changes in bacterial traits
Caused by:
Changes in environmental conditions
(only phenotypic changes)
Changes in the genetic codes
1- Intermicrobial exchange
2- Mutations
(point mutations, insertions, deletions)
Intermicrobial exchange
Transformation
(Capturing DNA from solution)
Transduction
(Phage-mediated)
Conjugation
(Bacterial Sex)
Original Transformation Exp.
F. Griffith (1928) using
pneumococci
DNA-Mediated Transformation
DNA-Mediated Transformation
Intermicrobial exchanges by vectors
Characteristics of genetic vectors
must be capable of carrying a significant piece
of donor DNA
must be readily accepted by the host
plasmids – small, well characterized, easy to
manipulate & can be transferred into
appropriate host cells through transformation
bacteriophages – have the natural ability to
inject their DNA into bacterial hosts through
transduction
8
Transduction
(madiated by phage)
Lytic versus Lysogenic
Generalized Transduction
Generalized Transduction
Transduction
Types of transduction
Generalized - Transduction in which
potentially any dornor bacterial gene can
be transferred.
 Specialized (Restricted):
Transduction in which only certain
donor genes can be transferred.
Restricted Transduction
(Lysogenic Phage)
bio
gal
gal
gal
bio
gal
bio
bio
bio
Transduction
Definition
Types of transduction
Significance
Common in Gram+ bacteria
Lysogenic (phage) conversion
• e.g. Corynebacterium diptheriae toxin
• Toxin derived from lysogenic phage
Conjugation
Conjugation
Definition: Gene transfer from
a donor to a recipient by direct
physical contact between cells
Mating types in bacteria
Donor
• F factor (Fertility factor)
F (sex) pilus
Donor
Recipient
• Lacks an F factor
Recipient
Conjugation
Significance
 Gram - bacteria
• Antibiotic resistance
 Gram + bacteria
• Production of adhesive material by donor
cells
Conjugation
Conjugation: Sex or F Pilus
Plasmids
Plasmids
Definition:
Extrachromosomal genetic elements that are
capable of autonomous replication (replicon)
Plasmid Types:
Congugative & Non-congugative
Episome - a plasmid that can integrate into the
chromosome
Casmid – An integration of a plasmid and a
bacteriophage
Phenotypic effects
Fertility (F factor)
Bacteriocinogenic (or encoding
some other toxins)
Resistance (R factors)
Structure of R Factors
RTF
RTF
Conjugative
plasmid
Transfer genes
R determinant
Resistance genes
R determinant
Self-Transmissible R Plasmid
Conjugation: F Plasmid Transfer
F+ and HFr cells
F+
Hfr
Integrated (Hfr)
(High Frequency of Recombination)
Hfr and F’ cells
Hfr
F’
Mechanism of Hfr x F- Crosses
Hfr
Hfr
F-
F-
Hfr
Hfr
F-
F-
Mechanism of F’ x F- Crosses
F’
F’
F-
F’
F’
F-
F’
F’
Transposable Genetic Elements
Definition: Segments of DNA that are able to
move from one location to another (across the
genome or from one genome to another)
Properties
“Random” movement
• Transposase
Transposition may be accompanied by
duplication
Types of Transposable Genetic Elements
Transposons (Tn)/ Insertion elements (IS)
Definition: Elements that carry other genes in
addition to those involved in transposition
Nomenclature - Tn10, IS6110
Structure
• Composite Tns
 Importance
IS
Resistance Gene(s)
IS
IS
Resistance Gene(s)
IS
• Antibiotic resistance
•Epidemiology and evolutionary studies