1. Bacterial Genetics
G.Jamjoom 2005

2. Bacterial Genetics Lecture Outline :
The study of bacterial genetics helped illustrate:
- the nature of genetic material as DNA
- the genetic code
- the nature of mutations (changes in nucleotide
sequences)
- regulation of gene function (repressors,
activators)

3. DNA Forms the Genetic Information:
- The Griffith experiment (1928,1944):
DNA fragments from capsulated pneumococcus can give noncapsulated strain the ability to make capsule -
“ transformation”

4. DNA Forms the Genetic Information:
- The Hershey and Chase experiment
Bacteriophage DNA alone enters the bacterial cell and makes new progeny phages. Phage protein coat remains outside and is not involved in this process.

6. Length of DNA In Different Organisms
- Bacteriophage MS2 Virus ,000 bp ~10 genes
- Bacteriophage T Virus ,000 bp ~ 200 genes
- Escherichia coli Bacterium ,000,000 bp ~4288 genes
- Saccharomyces Yeast ,000,000 bp
- C. elegans Nematode ,000,000 bp
- A. thaliana plant ,000,000 bp
- Drosophila Insect ,000,000 bp
- Mouse Mammal ,000,000,000 bp
- Human Mammal ,500,000,000 bp ~ 40,000genes

7. Bacterial Genetics Lecture Outline:
Prokaryotic cells, Eukariotic cells, Archae

8. EUKARYOTES
PROKARYOTES
BACTERIA
ARCHAEA

9. Prokaryotes Eubacter "True" bacteria Archaea human pathogens
clinical or environmental
one kingdom
Archaea
Environmental organisms
second kingdom

10. Bacterial Genetics Lecture Outline: 3. The bacterial chromosome :
- structure, genes, operons
- mapping
- complete sequences of selected bacteria
- replication, transcription, translation

16. The Bacterial Chromosome
Most bacterial chromosomes are circular
Many have been fully sequenced
Many genes have been identified and mapped using gene transfer techniques such as conjugation, transduction, and transformation

17. The Complete Sequence of Escherichia coli Chromosome

18. Echerichia coli chromosome
Size 4,600,000 base pairs (4.6 megabases)
Contains 4288 genes ( 62% identified)
Many genes code for the following :
- Cell structure
- Energy metabolism
- Proteins form DNA replication
- Proteins for transcription, translation, RNA
synthesis
- Synthesis of amino acids , nucleotides, etc.
- Synthesis of enzymes
Contains transposons and plasmid and phage sequences

20. Bacterial Genetics Lecture Outline:
G.Jamjoom 2005
Lecture Outline:
Bacteriophages (bacterial viruses):
- virulent
- temparate:
lysogey

23. Phage Composition and Structure
Head/Capsid
Genomic DNA
Contractile Sheath
Tail
Tail Fibers
Base Plate

24. Types of Bacteriophage
Lytic or virulent :
Phage that multiply within the host cell,
lyse the cell and release progeny phage (e.g. T4)
Lysogenic or temperate phage:
Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g., )
Expression of most phage genes repressed
Prophage – Phage DNA in the quiescent state
Lysogen – Bacteria harboring a prophage

25. Bacterial Genetics Lecture Outline: - functions
Plasmids (extrachromosomal elements):
- functions
- role in antibiotic resistance (R plasmids)

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

27. Plasmid- Coded Functions
Fertility
Resistance to:
- antibiotics
- irradiation
- phages
Production of :
- exotoxins
- enterotoxins
- bacteriocins
- Proteases
(cheese)
Metabolism of :
- various sugars
- hydrocarbons
Tumergenesis in
plants

28. Bacterial Genetics Lecture Outline:
Mechanism of gene transfer in bacteria:
- Transformation
- Transduction
- Conjugation

29. Transformation
Steps
Uptake of DNA
Gram +
Gram -
Recombination

30. 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

31. Generalized Transduction
Infection of Donor
Phage replication and degradation of host DNA
Assembly of phages particles
Release of phage
Infection of recipient
Homologous recombination
Potentially any donor gene can be transferred

32. Events Leading to Lysogeny
gal
bio
Site-specific recombination
Phage coded enzyme
Repression of the phage genome
Repressor protein
Specific
Immunity to superinfection

33. Termination of Lysogeny
Induction
Adverse conditions
Role of proteases
recA protein
Destruction of repressor
gal
bio
gal
bio
gal
bio
Gene expression
gal
bio
Excision
Lytic growth

34. Specialized Transduction Lysogenic Phage
Excision of the prophage
gal
bio
Replication and release of phage
Infection of the recipient
Lysogenization of the recipient
Homologous recombination also possible

35. Conjugation
Donor
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
Recipient
Lacks an F factor

36. Physiological States of F Factor
Autonomous (F+)
Characteristics of F+ x F- crosses
F- becomes F+ while F+ remains F+
Low transfer of donor chromosomal genes F+

37. Physiological States of F Factor
Integrated (Hfr)
Characteristics of Hfr x F- crosses
F- rarely becomes Hfr while Hfr remains Hfr
High transfer of certain donor chromosomal genes F+
Hfr

38. Physiological States of F Factor
Autonomous with donor genes (F’)
Characteristics of F’ x F- crosses
F- becomes F’ while F’ remains F’
High transfer of donor genes on F’ and low transfer of other donor chromosomal genes
Hfr F’

39. Mechanism of F+ x F- Crosses
Pair formation
Conjugation bridge F+ F-
DNA transfer
Origin of transfer
Rolling circle replication

40. Mechanism of Hfr x F- Crosses
Pair formation
Conjugation bridge
Hfr F-
DNA transfer
Origin of transfer
Rolling circle replication
Homologous recombination

41. Mechanism of F’ x F- Crosses
Pair formation
Conjugation bridge F’ F-
DNA transfer
Origin of transfer
Rolling circle replication

42. Conjugation Significance Gram - bacteria Gram + bacteria
Antibiotic resistance
Rapid spread
Gram + bacteria
Production of adhesive material by donor cells

43. Bacterial Genetics Lecture Outline: Transposons (jumping genes) :
G.Jamjoom 2005
Lecture Outline:
Transposons (jumping genes) :
- role in antibiotic resistance

44. Transposons (Transposable Genetic Elements)
Definition: Segments of DNA that are able to move from one location to another
Properties
Inverted terminal repeat sequences (loop formation)
“Random” movement from one DNA site to another
Not capable of self replication (not a replicon)
Transposition mediated by site-specific recombination
Transposase
Transposition may be accompanied by duplication

45. Examples of Antibiotic Resistance Transposons
Tn ampicillin
Tn kanamycin
Tn Trimethoprim
Tn Chloramphenicol
Tn Tetracyclin
Tn erythromycin

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

47. Mechanism of Plasmid-Mediated Resistance
Production of enzymes for :
- Hydrolysis of β-lactam ring
- phosphorylation
- adenylation
- acetylation
- methylation
- modification of permeability
- other

48. Control of Gene Expression
Transcriptional control
Clustering of genes with related function
Coordinate control of genes with related function
Polycistronic mRNA

49. Inducible Genes - Operon Model
Definition: Genes whose expression is turned on by the presence of some substance
Lactose induces expression of the lac genes
An antibiotic induces the expression of a resistance gene

50. Lactose Operon Structural genes Regulatory gene Operator Operon
lac z, lac y, & lac a
Promoter
Polycistronic mRNA
Regulatory gene
Repressor
Operator
Operon
Inducer - lactose i
Operon
RegulatoryGene p o z y a
DNA
m-RNA
-Galactosidase
Permease
Transacetylase
Protein

51. Lactose Operon Inducer -- lactose Negative control Absence Presence pz y a
No lac mRNA
Absence of lactose
Active
Inducer -- lactose
Absence
Active repressor
No expression i p o z y a
-Galactosidase
Permease
Transacetylase
Presence of lactose
Inactive
Presence
Inactivation of repressor
Expression
Negative control

52. Bacterial Genetics Lecture Outline: Genetic Engineering
- Synthesis of human proteins in
bacteria, e.g. insulin, interferon
- DNA vaccines