Microbiology 251- Test 2: Ch 10/11

How do microbes adapt to their environment?

-Gene regulation/expression (switching genes "on" and "off", only using necessary genes)
-Gene changes (mutation, transduction, etc.)

In what two ways do bacteria undergo genotypic changes?

-Mutation (change in DNA sequence)
-Gene Transfer (Transformation, Transduction, Conjugation)

What is vertical gene transfer?

-From generation to generation
-Mutations are passed to progeny cells

What is horizontal gene transfer?

Genes acquired from cells of the same generation (transduction, conjugation, transformation)

What are the basic features of plasmids?

-DNA not part of chromosome and NOT essential to cell life
-Small
-Circular
-Double Stranded
-Narrow host range
-Can carry genes for antibiotic resistance

What is an R plasmid

Resistance plasmid (antibiotic resistance)

What kinds of genes may be coded on plasmids?

-Non-essential, beneficial genes
-Antibiotic resistance
-Virulence factors (toxins)

What do plasmids need in order to transfer?

A living host

Explain Transformation

-Cell takes up prokaryotic DNA directly from the environment -The DNA may remain separate as plasmid DNA or be incorporated into the host genome.

Explain Transduction

-A bacteriophage injects DNA that is a hybrid of viral DNA and DNA from previously infected bacterial cell

Explain Conjugation

-Cells of the same generation make contact with each other, forming "bridge" and exchange genetic material
-BOTH cells must be alive for this to occur

How did the "Detection of Gene Transfer in Bacteria" experiment work?

-Two agar plates were plated with separate strains (one His-/Trp-, one Leu-/Thr-)
-When plated individually, no growth
-When cultured together, ample growth occurred
-Proved that bacterial cells can share genetic information to promote survival

Explain the steps of the Griffith experiment

-Living encapsulated cells (S strain) injected into mouse (it dies)
-Living non-encapsulated cells (R strain) injected into mouse (no affect)
-Heat-killed encapsulated cells (S) injected into mouse (no affect)
-Heat-killed encapsulated S cells + live R cells injected into mouse (it dies)

Explain the importance of the Griffith experiment

-It showed proof of transformation (otherwise the mouse with the mixed cell injection would not have died)

The case study of the patient Dx with cholera showed which mode of bacterial gene transfer?

-Transduction (toxin produced/virulence factor via lysogenic phage)

The case study of the patient Staphylococcus aureus skin infection that was treated with antibiotics showed which mode of bacterial gene transfer?

-Transduction (introduction of prophage, often induced by introduction of antibiotics)

What give Bacillus anthracis its virulence factor (as compared to B. cereus which it shares 99% of genome with)?

-Two large plasmids encoding for lethal toxins (anthrax)

What is a mutagen?

-Agent/chemical that induces mutations

What is a mutant?

-Mutated cell

What are wild-type cells?

Non-mutated cells

What are they common types of gene mutation?

-Spontaneous (errors in encoding/rare)
-Induced (chemicals, radiation)
-Base substitution (most common)
-Base deletion/addition (frameshift mutation)
-Reversion (change back to wild-type)

Explain the experiment for selecting for mutation

-Streptomycin culture (containing sensitive and resistant cells) was added to plates with and without streptomycin antibiotic
-Agar with antibiotic showed only one growth, showing a single mutated cell that is resistant to the antibiotic
-Looks identical to the cells on non-antibiotic plate

What are bacterial mutagenesis assays used for?

Identifies potential carcinogens

Explain the Ames assay

-Uses Salmonell typhimurium strain that cannot make Histidine

-Grows strain in normal media (control) and media containing potential mutagen

-If growth occurs on potential mutagenic plate, then the product is mutagenic (as it has to mutate Histidine production to grow)