Bacterial Genetics

Question 1

what are the three ways MGEs move between bacteria?

Answer 1

1. Bacterial transformation
   A donor bacteria that has usually died and this has released its DNA into the environment and then a recipient bacteria that has figured out how to take up the DNA
   
   2. Bacterial transduction
      Viruses whose genome sit in the chromosome, they can be induced under stressful conditions. These phage viruses are made, DNA is packaged inside the phage and delivered to recipient cells where the phage binds to the surface of the bacteria and injects their DNA which then incorporates into the new cell
   3. Bacterial conjugation
      This is where you have a plasmid, may have just its own genes or another mobile genetic element called a trans boson, that can hop from one site to another that can do conjugation. The plasma then encodes the gene necessary to make a pilus or a pore that requires cell-cell contact, do the plasma replicates and transfers a new copy of itself into the cell

Question 2

What is generalised transduction?

Answer 2

Generalised Transduction- temperate bacteriophage ‘accidentally” packages host bacterial DNA or plasmids into phage particles and delivers it to new bacteria

Question 3

What environmental triggers are bacteria highly responsive to?

Answer 3

Bacteria are single-celled organisms that are highly responsive to environmental triggers
Triggers include:
Nutrients
Oxygen
Iron
Temperature
Bacterial pheromones
Mammalian cells, hormones etc.
They do this through a Two Component Signal Transduction
The bacteria produces a receptor on the cell surface that can bind to something that’s relevant to the condition triggers

Question 4

How is a knockout made?

Answer 4

Construction of a knockout

1. Clone virulence gene into 'suicide vector' plasmid (no origin for replication)
2. Clone antibiotic resistance marker into the gene to disrupt it
3. Transform it into bacterial cell
4. Recombination via RecA protein, rare 
5. Plate onto agar with antibiotic and select for the rare isolate that has the resistance marker

Question 5

What does the bacterial genome include?

Answer 5

All the DNA in a bacterial call
Includes:
Chromosome (single copy, circular, essential for life)
Mobile genetic elements (MGE), such as:
Plasmids (autonomously replicating circular DNA
Prophage (viruses integrated into the chromosome)
E.g. MRSA strain 252 chromosome is 2.9 million bp and carries integrated prophage, transposons, pathogenicity islands, antimicrobial resistance elements etc.
Encodes- 2800 genes