Genetic Variation, Gene Transfer and the Evolution of Virulence

Question 1

Describe the mechanisms that generate genetic diversity within a bacterial species and how these contribute to the evolution of virulence.

Answer 1

Spontaneous mutation, recombination, Acquisition of new DNA

Question 2

Discuss how spontaneous mutation and selection can interact to determine the genetic composition of bacterial populations.

Answer 2

Basically darwinian evolution mechanics, single point mutations, del, and ins occur randomly and sometimes confers an survival advantage.

Mutation rates are 10^-6 to 10^-10 per cell generation

Question 3

Bacterial Transformation

Answer 3

When a bacteria takes from DNA fragments from the environment (e.g. from lysed cells) which can confer virulence or other genes

Seen in several bacteria, (+) and (-)

Question 4

Bacterial Transduction

Answer 4

Gene transfer mediated by bacteriophage

Question 5

Bacterial Conjugation

Answer 5

Form of genetic transfer that is dependent upon physical contact between donor and recipient, usually through transfer of plasmids

Paradigm: Plasma F, which helps with conjugation

Question 6

Bacterial Viruses (Bacteriophages)

Answer 6

Viruses evolved to target bacterium.

Attaches to cell wall and injects viral nucleic acid into the cytoplasm, where it is replicated, transcribed and translated.

Question 7

Bacteriophages- Lytic State

Answer 7

Multiplication and proliferation leading to host cell lysis

Question 8

Bacteriophages- Lysogenic State

Answer 8

Host cell remains viable and alive, and phage DNA is maintained in microbe genome as a prophage

Question 9

Describe how errors in bacteriophage development can lead to phage-mediated gene transfer.

Answer 9

As a consequence of DNA packaging

Sometimes when packing the viral DNA into a new phage, some of the host DNA will be incorporated. When in a new host, these DNA segments can recombine to produce recombinants

Question 10

Generalized Transduction

Answer 10

Process in which any segment of donor cell genome may be passed to another cell

Question 11

Transposon

Answer 11

A discrete segment of DNA that can move itself or a copy of itself to different chromosome locations

Can be conjugative (not like plasmid though)

Question 12

Bacteriophage Conversion (AKA lysogenic conversion)

Answer 12

When virulent genes (or other phenotypes) are carried on a bacteriophage and are not a “normal” part of a given microbe’s genome

“In lysogenic conversion the genes
controlling the new phenotypic trait are found only as a component of the phage genome”

Question 13

Plasmid

Answer 13

A small circular piece of DNA usually, but not always, containing genes that encode for survival benefits in the form of atbx resistance, novel functions, or virulent genes

Can be conjugative (self mobilizing/transferable) , non conjugative (can be passively transferred), mobilizable.