Transcript DNA-Mediated Transformation

Bacterial Ecology
Bacterial Ecology
Definition
- Relation between bacteria and non-living
environment
- Relation between bacteria and other living organisms
- Relation between bacteria with each other
Relation with non-living environment
Bacteria plays roles as:
Production
Producers
Degradation
Degeneraters
Consumers
Relation with other living organisms
(Symbiosis)
Mutualism
(Transient and resident microflora)
Commensalism
Parasitism
Relation with each other
(Symbiosis)
Indifference
Competition
Antagonism
Synergism
Bacterial Genetics
(Studying heritage variations in bacterial traits)
Bacterial traits changes are due to:
1. Changes in environmental conditions
2. Changes in the genetic codes
Changes in environmental conditions
Brucella species are bacillus in 21 ○C and
coccobacillus in 37 ○C
Mycobacterium tuberculosis shows filamentous in 24
○C when exposing glycerin.
pneumococcus loses its capsule after some invitro
culture.
Staphylococcus aureus is not able to produce golden
pigment in absence of oxygen.
Salmonella species loses flagella when exposing
phenol on culture.
Adding calcium to Bacillus anthracis culture stops
converting bacteria to spore form.
Changes in bacterial traits
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)
Transformation
Explored by F. Griffith (1928) using pneumococci
The DNA released from a degenerated bacterium
enters into another bacterium.
There is no vector or mediation in this type of gene
exchange.
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
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Transduction
(madiated by phage)
Microbe Library, American Society for Microbiology
www.microbelibrary.org
Lytic versus Lysogenic
Generalized Transduction
Generalized Transduction
Transduction
Specialized (Restricted):
Transduction in which only certain donor
genes can be transferred.
Transduction
(Restricted)
Restricted Transduction
(Lysogenic Phage)
bio
gal
gal
gal
bio
gal
bio
bio
bio
Transduction
Significance
– Common in Gram+ bacteria
– Lysogenic (phage) conversion
• e.g. Corynebacterium diptheriae toxin
–Toxin derived from lysogenic phage
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
Recipient
Lacks an F factor
Donor
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
Conjugative
plasmid
Transfer genes
RTF
R determinant
Resistance genes
R determinant
Self-Transmissible R Plasmid
Conjugation: F Plasmid Transfer
Conjugation
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
 Antibiotic
resistance
Epidemiology and
evolutionary studies
IS
Resistance Gene(s)
IS
IS
Resistance Gene(s)
IS