Bacterial genetics

Question 1

Define the method of DNA integration

• Ability to take up naked DNA (from cell lysis) from environment (also known as competence).
• A feature of many bacteria (S. pneumoniae, H. influenzae type B, Neisseria: SHiN)
• Any DNA can be used
• **adding deoxyribonuclease **to environment will degrade nake DNA in medium–> no transformation seen!

Answer 1

Transformation

Question 2

Define the type of conjugation

• F+ plasmid contains genes required for sex pilus and conjugation
• Bacteria without this plasmid are termed F-
• Plasmid (dsDNA) is replicated and transferred through pilus from F+ cell.
• No transfer of chromosomal genes.

Answer 2

F+ x F-

Question 3

Define the type of conjugation

• F+ plasmid can become incorporated into bacterial chromosomal DNA
• termed high freq recombination (Hfr) cell
• Replication of incorporated plasmid DNa may include some flanking chromosomal DNA
• Transfer of plasmid and chromosomal genes.

Answer 3

Hfr x F-

Question 4

Define the method of DNA integration

• Segment of DNA (trasposon) that can ‘jump’ (excision adn reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa
• When excision occurs may include some flanking chromosomal DNA, which can be incorporated into a plasmid and transferred to another bacterium
• Examples include antibiotic resistance genes on R plasmid

Answer 4

Transposition

Question 5

Define the type of transduction

• A packaging event
• Lytic phage infects bacterium, leadign to cleavage of bacterial DNA
• Parts of bacterial chromosomal DNA may become packaged in viral capsid
• Phage infects another bacterium transferring these genes.

Answer 5

Generalized transduction

Question 6

Define the type of transduction

• An ‘excision’ event
• Lysogenic phage infects bacterium; viral DNA incorporates into bacterial chromosome.
• When phage DNA is excised, flanking bacterial genes may be excised with it.
• DNA is packaged into phage viral capsid and can infect another bacterium

Answer 6

Specialized transduction

Question 7

Define 5 bacterial toxins that are encoded in lysogenic phage due to specialized transduction.

(ABCDE)

Answer 7

• ShigA-like toxin
• Botulinum toxin (certain strains)
• Cholera toxin
• Diphtheria toxin
• Erythrogenic toxin of streptococcus pygoenes