1. Bacterial heredity and variation

2. Bacteria genetic material Bacteriophages
Main contents
Bacteria genetic material
Bacteriophages
Mechanisms of genotypic variation
Medical application of bacteria variation

3. Bacterial genetics Genotypic variation DNA sequence change
Heredity
Variation
Genotypic variation
DNA sequence change
Heritable, irreversible
Phenotypic variation
Occurs when the expression of gene is changed in response to its environment, reversible, inheritable

4. Bacteria genetic material
Bacterial chromosome
Plasmid
Transposable element

5. Chromosome (nucleoid)
A circular, double-stranded DNA

6. About 1000μm long
Small genome
Operon structure
No intron
Translation follow transcription almost at the same time
Absence of non-encoding region
No gene overlapped
Haploid except rRNA

7. Plasmid extrachromosomal genetic elements
Closed-circular, double-stranded DNA
Characteristics
Self-replication
Encoding some bacterial properties
F plasmid, R plasmid, Col plasmid, Vi plasmid

8. Not necessary for bacterial viability
Transferability
Transformation, conjugation, transduction
Conjugative plasmid and nonconjugative plasmid
Plasmid compatibility and incompatibility

9. Transposon,Tn
A segment of DNA that is capable of moving to a new position within the same or another chromosome, plasmid, or cell and thereby transferring genetic properties.
Twp types
Insertion sequence (IS)
Complex transposon (Tn)

10. Tnp, resistance, enterotoxin, etc
IS and Tn
transposase
ABCDEF
F’E’D’C’B’A’
( IR )
(inverted repeats) IS
Tnp, resistance, enterotoxin, etc Tn IR
1.细菌DNA分子中(核质,质粒)可自行移位的一个片段。
2.种类:
①插入序列(IS）
只有转位基因：→插入基因内部
→阻断基因的连续性
→导致突变。
②转座子(Tn)---跳跃基因
转位基因+遗传信息：→转位→突变
Consequence:
Drug resistance variation transmission

11. Bacteriophage (phage)
Definition
Viruses that infect bacteria,fungi,actinomycetes or spirochetes
Obligate intracellular parasite
Strict specificity
Widely distributed

12. Bacteriophage (phage)
Shape and structure
tadpole, spherical, filamentous
Chemical composition
Nucleic acid(DNA or RNA)
Protein
Type of reproduction
Self-Replication
tail

13. Bacteriophage (phage)
Life cycle
Virulent phage—Lytic phage
Lytic life cycle
Temperate phage –Lysogenic phage
Lysogenic life cycle

14. Bacteriophage (phage)
Virulent phage
Lytic life cycle
Adsorption
Penetration
Biosynthesis
Maturation
Release

15. Bacteriophage (phage)
Temperate phage
Prophage
Phage genome integrating with bacterial genomes.
Lysogenic bacteria
bacteria containing prophages
Two life cycles
Lysogenic and lytic
Lytic cycle
Lysogenic cycle

16. Bacteriophage (phage)
Medical significance
Identification and typing of bacteria
Contribution to genetic transfer and recombination of bacteria

17. Mechanism of genetic variation
Mutation
Genetic transfer and recombination
Transformation
Transduction
Conjugation
Lysogenic conversion

18. Gene mutation Gene mutation any change to the sequence of bases in
the DNA of an organism
Wild type and mutant
point mutations--- single base change
nucluotide base insertion,deletion and subsitution—transition and transversion
large piece of DNA mutation
DNA inversion,duplication and deletion
frameshift mutation

19. types of large DNA sequence mutation
Wild type
inversion
duplication
deletion
substitution
insertion
types of large DNA sequence mutation
A～G、X mean different DNA fragement

20. Gene mutation rules low frequency sponteneously---10-10-10-6
greatly increased rate induced by mutagen
randomly and non-directionally
reversion of gene mutation
forward mutation
Wild type mutant
Reverse mutation

21. 影印试验(replica plating)
(Lederberg 1952)

22. Gene transfer and recombination
Unidirectional: donor to recipient
Gene recombination
New biological properties in recipient cells

23. Definition Transformation
A process by which a bacterium directly takes up a free DNA fragment and then incorporate it into the recipient bacterial genome, resulting in the alteration of bacterial genetic constitution.

24. The discovery of transformation (1928 Griffith)

25. S colony
R colony

26. Transformation Chromosomal DNA Plasmid DNA Bacteriophage DNA
Free DNA transferred by transformation
Chromosomal DNA
Plasmid DNA
Bacteriophage DNA
conditions
<10-20 genes
High homology between donor and recipient
Under the competent condition

28. Conjugation Definition
A process by which there is a transfer of DNA from a living donor bacterium to a recipient bacterium by cell-to-cell contact.
Often involves a sex pilus.

29. Conjugation DNA transferred by conjugation
Plasmid(F plasmid or R plasmid)
Chromosomal segment
The donor bacterium
F+ or male
The recipient bacterium
F- or female

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

31. R plasmid conjugation Components Resistance transfer factor(RTF)
Resistance determinant (r-det)
Medical significance
Transmission of antibiotic resistance between bacteria

32. R plasmid
Tn 9
Tn 21
Tn 10
Tn 8
RTF
R determinant

33. R plasmid conjuagtion

34. Transduction Definition
A process by which a DNA fragment is transferred from one bacterium to another by a bacteriophage.
Two types
Generalized transduction
Specialized transduction

35. Generalized transduction

36. Generalized transduction
Larger piece of DNA can be transferred by transduction compared to transformation
More efficient than transformation
Two consequences
Complete transduction
Abortive transduction

38. Specialized transduction
gal
bio

39. Specialized transduction

41. Lysogenic conversion Definition
A process by which a temperate phage injects its own genome into a host bacterium to make the host a lysogeny.
e.g., Diphtheria toxin
(Corynebaterium diphtheriae)

42. Medical application of bacteria variation
Application in diagnosis of bacterial infectious disease
Preventing antibiotics resistance bacteria strain transmission
Bacteria vaccine
The application in discovering cancer-inducing substances
Application in genetic engineering

43. V.cholera
L-form