bacterial physiology and genetics

Question 1

fermentation vs respiration

Answer 1

fermentation:

• organic compounds are electron donors/acceptors (does not require O2)
• energy generated by substrate level phosphorylation = less efficient
• endproducts (acids) accumulate in media

respiration:

• O2 is terminal electron acceptor for aerobic; NO3- is terminal electron acceptor for anaerobic
• proton motive force is created, allowing for ATP generation via chemiosmosis
• very efficient => more rapid growth

Question 2

oxidase test

Answer 2

• detects bacteria with cytochrome c in their ETC (psa, neisseria, etc)
• test: oxidase will oxidize N,N-dimethyl-p-phenylenediamine => color change

Question 3

pros and cons of oxygen

Answer 3

• aerobic respiration => faster growth

- generation of free radicals: H2O2 and superoxide

Question 4

enzymatic requirements of aerobes

Answer 4

superoxide dismutase: breaks down superoxide into h2o2 and o2

catalase: breaks down h2o2 into water and o2

Question 5

different bacterial oxygen tolerances

Answer 5

aerobes: require oxygen, cannot ferment, + enzymes
anaerobes: killed by oxygen, ferment, - enzymes

facultative anaerobes: respire with oxygen, ferment without oxygen, + enzymes

indifferent (aerotolerant): ferment +/- oxygen, + enzymes

microaerophilic: prefer low oxygen

Question 6

categories of media

Answer 6

complex = rich; digests of materials

minimal = only essential components needed for growth of certain bacteria

enrichment = promotes growth of certain organisms

selective = inhibits growth of certain organisms

differential = allows distinction between colonies of different organisms

Question 7

bacterial growth phases

Answer 7

lag -> log -> stationary

Question 8

transformation

Answer 8

uptake of pieces of naked DNA from the environment and incorporation into chromosome (naturally and artificially competent)

Question 9

transduction

Answer 9

bacteriophages act as vectors to introduce DNA from donors to recipients via infection

generalized: mis-packaging and inclusion of host DNA into phage capsid
specialized: imprecise excision of phage DNA from host chromosome leads to packaging of host DNA with phage DNA

Question 10

conjugation

Answer 10

cell-cell contact allowing for unidirectional transfer of genetic material (F plasmid)

Question 11

transposable elements (general, and specific types)

Answer 11

mediate their own movement from one location on the chromosome or a plasmid to another

insertion sequences = small; inverted repeats flanking transposase genes => transposase recognizes repeats and catalyzes cutting and resealing of DNA allowing movement

transposons = larger elements that carry genes (resistance, virulence, etc) in addition to transposases. may or may not be flanked by IS elements but require some inverted repeats

Question 12

plasmids

Answer 12

small, extrachromosomal circular dsDNA that can replicate independently of host chromosome

nonconjugative: can’t mediate their own horizontal transfer

conjugative plasmids: capable of transferring themselves (ex: R plasmid that carries resistance genes)

Question 13

virulence determinants carried by plasmids

Answer 13

E. coli enterotoxins (LT and ST)

Shigella type III secretion system

C. tetani tetanus toxin

Question 14

phages

Answer 14

viruses that infect bacteria

virulent: cause lytic infection
temperate: cause lysogenic infection

Question 15

phage conversion

Answer 15

when infection by a phage leads a bug to acquire new properties

Question 16

virulence determinants carried by phages

Answer 16

GAS exotoxins
botulinum toxin
cholera toxin
diphtheria toxin
shiga-like toxins

Question 17

integrons

Answer 17

genetic entities that capture exogenous gene cassettes and ensure their expression.

contain:

1. outward oriented promoter
2. primary recombination site downstream of promoter
3. gene encoding an integrase which can incorporate gene cassettes into the integron

integron is not mobile unless incorporated into a different mobile element

multiple cassettes can be inserted into the same integron forming an operon