Basic Bacteriology: Bacterial Genetics

Question 1

What is bacterial transformation?

What bacteria can do it?

Answer 1

Transformation: Ability to take up naked DNA (from cell lysis) from the environment (also known as competence).

Many bacteria, including S. pneumoniae, H. influenzae type B, and Neisseria (SHiN)

Any DNA can be used, adding deoxyribonuclease to environment will prevent transformation by degrading naked DNA.

Question 2

What is conjugation?

Answer 2

Bacterial mating. Involves transfer of an F+ plasmid.

Question 3

Describe characteristics of F+ x F- conjugation.

Answer 3

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

Question 4

Describe characteristics of Hfr x F- conjugation.

Answer 4

F+ Plasmid can become incorporated into bacterial chromosome DNA - called high-frequency recombination (Hfr) cell. Replication of incorporated plasmid DNA may include flanking chromosomal DNA.

Transfer of plasmid and chromosomal genes.

Question 5

What is transposition?

Major example?

Answer 5

Segment of DNA (a transposon) that can “jump” (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice-versa.

When excision occurs, may include flanking chromosomal DNA, which can be incorporated into a plasmid and transferred to another bacterium.

Examples include antibiotic resistance genes on R plasmid.

Question 6

What is transduction?

Described generalized transduction.

Answer 6

Transmission of genetic material between bacteria via viruses.

Generalized: A “packaging” event. Lytic phage infects bacterium, bacterial DNA is cleaved, parts of bacterial chromosomal DNA may be backaged in viral capsid. Phage infects another bacteria, transmitting genes.

Question 7

Describe specialized transduction.

What 5 bacterial toxins are transmitted/encoded in this way?

Answer 7

Specialized transduction: An “excision” event. Lysogenic phage infects bacterium, viral DNA is incorporated into bacterial chromosome. When viral DNA is excised, flanking bacterial genes may be excised with it. This DNA is packaged with the virus and may be transmitted to another bacterium.

ABCDE toxins are encoded in a lysogenic phage:

ShigA-like toxin

Botulinim toxin (certain strains)

Cholera toxin

Diphtheria toxin

Erythrogenic toxin of Streptococcus pyogenes