Chapter4 Heredity and variation of bacteria Xin Gang Department of microbiology and immunology Shantou University Medical College

Genetic materials of bacteria Mechanism of variation outline Concepts Genetic materials of bacteria Mechanism of variation

concepts Heredity Variation Genotypic variation Phenotypic variation

Variation of bacteria Variation in morphology and structure lose capsule (Pneumococcus) H O Lose Spore L-form

Variation Variation in virulence Bovine TB BCG C. diphtheriae 13years, 230 generation C. diphtheriae b-corynephage, diphtheriae toxin

Variation Variation in drug resistance Variation in colony Penicillin resistant strains of staphylococcus aureus Variation in colony S-R Variation in enzyme activity Phenotypic Genotypic

I Genetic materials of bacteria Chromosomes Plasmids Phage Transposable elements

1 Chromosomes DNA forms: ds-DNA, circle

Rolling-circle pattern of replication Size E.coli 1300mm, 4288gene Rolling-circle pattern of replication

2 Plasmids Extrachromosomal genetic elements that are capable of autonomous replication. Small double-stranded DNA molecules, usually circular exist independently of host chromosome autonomously replicating (replicon) may disappear spontaneously or by induction (UV) incompatibility and compatibility

Classification of Plasmids Transfer properties Conjugative 40-100kbp eg. F, R plasmid Nonconjugative <15kbp, transfer by mobilization eg. ColE1 plasmid

Phenotypic effects Fertility plasmid,F plasmid coding sex pilus Resistance plasmid, R plasmid resistance transfer factor resistance determinant Tn 9 Tn 21 Tn 10 Tn 8 RTF Virulence plasmid Coliciogenic plismid R determinant

3 Bacteriophage, phage T4 bacteriophages infecting E.coli.

Bacteriophage (Phage) Definition Bacterial virus. Virus of bacteria, fungi, actinomyces, and spirochete.

Composition and Structure Nucleic acid DNA or RNA Protein Protection Infection

Structure (T4) Head or capsid Tail Head/Capsid Contractile Sheath Tail Tail Fibers Base Plate

Infection of Host Cells Attachment Sheath contraction Nucleic acid injection

Attachment and injection

Types of Bacteriophage Lytic or virulent phage (e.g., T4) Lysogenic or temperate phage (e.g., l)

Virulent Phage Lytic or virulent phage Phage that can only multiply within bacteria and kill the cell by lysis. (e.g., T4)

Lytic Phage Multiplication Cycle

Lytic cycle Attachment Injection and uncoating Biosynthesis Eclipse Early proteins Phage DNA synthesis Late proteins Intracellular accumulation Maturation and releasing

Lysogenic Phage Lysogenic or temperate phage: Prophage Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g., l) Prophage Lysogen,Lysogenic bacterium Lysogenic conversion

Lysogenic phage /temperate phage Lysogenic bacterium /lysogen prophage

Lysogenic or phage conversion Definition: A change in the phenotype of a bacterial cell as a consequence of lysogeny Modification of Salmonella O antigen Toxin production by Corynebacterium diphtheriae

Lytic versus lysogenic infection by phage Lambda

4 Thransposable element Concept Segments of DNA that are able to move around the genome. Properties “Random” movement Jumping genes or movable genes First discovered in the 1940s by Barbara McClintock during her study on maize genetics.(won the Nobel prize in 1983)

Types of Transposon Insertion sequences (IS) Importance A short sequence of DNA containing only the genes for those enzymes required for its transposition. Importance Mutation Plasmid insertion IR: inverted repeat

Types of Transposon Transposons (Tn) or complex Tn Importance contain genes other than those required for transposition (eg. Antibiotic resistance or toxin genes) Importance Antibiotic resistance

II mechanism of variation Mutation Gene transfer and recombination

i Mutations in bacteria Changes in DNA sequences Base substitutions, deletions, insertions, rearrangements Spontaneous mutation: 10-8-10-6 Backword mutation or reverse mutation

ii Gene transfer and recombination Transformation Transduction Conjugation Lysogenic conversion protoplast fusion

General Features of Gene Transfer in Bacteria Unidirectional Donor to recipient Donor does not give an entire chromosome Gene variation can occur between species

1 Transformation Definition: Gene transfer resulting from the uptake of DNA from a donor. Competence of the recipient (Bacillus, Haemophilus, Neisseria, Streptococcus)

Griffith’s transformation experiments

Bacterial Transformation With DNA Fragments

2 Conjugation Donor Definition: Donor DNA transferred to recipient cell through sex pilus. Recipient

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

Physiological States F plasmid Hfr Hfr, high frequency of recombination Hfr F’ F’ plasmid

Mechanism of Hfr x F- Crosses

Mechanism of F’ x F- Crosses

Resistance plasmid, R plasmid RTF (resistance transfer factor) transfer genes code pili R determinant (resistance determination ) resistance genes transponsons Tn 9 Tn 21 Tn 10 Tn 8 RTF R determinant

3 Transduction Definition: Gene transfer from a donor to a recipient by way of a bacteriophage

Types of transduction Generalized - Transduction in which potentially any donor bacterial gene can be transferred Specialized (restricted) - Transduction in which only certain donor genes can be transferred

Generalized transduction by bacteriophages

Generalized Transduction Infection of Donor Phage replication and degradation of host DNA Assembly of phages particles Release of phage Infection of recipient Legitimate recombination

specialized transduction by a temprerate bacteriophage

specialized transduction gal bio specialized transduction

lysogenic conversion DNA recombination protoplast fusion

Practical implications Application in diagnosis, treatment and prevention of infectious diseases Eg. L-form PCR Detection of mutagenicity Application in genetic engineering

The Ames Test for mutagenicity