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

Intermicrobial exchanges by vectors

7 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

Transduction (madiated by phage)

Microbe Library, American Society for Microbiology

Lytic versus Lysogenic

Generalized Transduction

Transduction Types of transduction – Generalized - Transduction in which potentially any dornor bacterial gene can be transferred. – Specialized: Transduction in which only certain donor genes can be transferred.

Transduction (specialized)

Specialized Transduction (Lysogenic Phage) gal bio gal bio gal bio gal bio gal

Transduction Definition Types of 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 Donor Recipient –Recipient Lacks an F factor

Conjugation Significance – Gram - bacteria Antibiotic resistance – Gram + bacteria Production of adhesive material by donor cells

Conjugation

Conjugation: Sex or F Pilus

Plasmids

Definition: Extrachromosomal genetic elements that are capable of autonomous replication (replicon) Episome - a plasmid that can integrate into the chromosome

Classification of Plasmids Transfer properties – Conjugative – Nonconjugative Phenotypic effects – Fertility – Bacteriocinogenic plasmid (or encoding some other toxins) – Resistance plasmid (R factors)

Structure of R Factors RTF – Conjugative plasmid – Transfer genes Tn 9 Tn 21 Tn 10 Tn 8 RTF R determinant –Resistance genes

Self-Transmissible R Plasmid

Conjugation: F Plasmid Transfer

Conjugation

F + and HFr cells Integrated (Hfr) (High Frequency of Recombination) F+F+ Hfr

Hfr and F’ cells Hfr F’

Mechanism of Hfr x F - Crosses HfrF-F- F-F- F-F- F-F-

Mechanism of F’ x F - Crosses 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 Resistance Gene(s)