Lecture 4 - Bacterial Gene Transfer Flashcards
Range of sizes of bacterial genomes
500 - over 4000 genes
Can bacterial chromosomes be linear?
Yes
Error rate of E. coli DNA replication
1 in 10 million - 1 in 100 million
SNP
Single Nucleotide Polymorphism
Codon bias
The ratio in a bacterial species of G-C nucleotides to A-T.
Normally balanced, but can be unequal.
How can protein expression be efficient or inefficient?
Codon bias in a bacterium can bias towards certain codons of one amino acid.
EG: Mycobacterium has ~75% G-C.
Phe can either be TTT or TTC. The TTC codon is more efficient, as there are more tRNAs with a C than with a T.
Is most bacterial DNA coding or non-coding?
Coding
Example of mutations controlling gene expression
bvgA, bvgS genes in B Pertussis
Contains a sequence of repeated C.
Adding or omitting a C results in a STOP codon.
This inactivates bvg.
Addition of mono-, di- or tetra- nucleotides restores function
Example of a bacterium that uses internal DNA recombination
Neisseria gonnorrhoeae
How do neisseria gonorrhoeae alter surface pili?
1)
2)
3)
1) pilS (silent) and pilE (expressed) genes exist.
2) pilS lacks a promotor region
3) Gene segment of pilS can be recombined into pilE, altering pilE pili.
When do bacteria lose function of parts of their genomes?
When they host adapt
How is chromosome location important for a gene?
1)
2)
1) When bacteria divide, DNA remains functional.
2) The closer a gene is to the origin of replication, the more time it spends as two copies of a gene while the chromosome divides
This is called ‘gene duplication.’
How is Salmonella typhi more adapted to humans than Salmonella typhimurium?
Has more pseudogenes (parts of genome inactivated)
How does a bacterium protect itself from it’s own restriction enzymes?
Particular methylation pattern on own genome
Three types of horizontal gene transfer
Transformation
Conjugation
Transduction
What is transformation?
Bacteria taking up genetic material from the environment
What is conjugation?
Bacteria transferring genetic material between one another using a sex pilus and a mating bridge
How do naturally competent bacteria ‘know’ which genetic material to pick up from the environment?
Species-specific DNA uptake sequences on genetic material
Is E. coli naturally transformable?
No
What is a transformasome?
An extracellular vesicle-like structure containing genetic material
Example of a bacterium that uses transformasomes
Haemophilus influenzae
What kind of genetic code is transferred across a mating bridge?
ssDNA
Examples of genes which could be horizontally transferred
Resistance plasmids
Transposons
Pathogenicity Islands
Name of cell giving DNA and cell receiving DNA in transformation
Donor cell and recipient cell.
Recipient cell progeny are called transformants
Examples of barriers to transformation
Restriction enzymes
Membranes
DNA-degrading environment
Experiment demonstrating transformation 1) 2) 3) 4)
By Fred Griffith, 1928
Used Streptococcus pneumoniae
1) Inject mice with capsulated bacteria, mice die.
2) Inject mice with uncapsulated bacteria, mice survive.
3) Inject mice with heat-killed capsulated bacteria, mice survive.
4) Inject mice with heat-killed capsulated bacteria and live uncapsulated bacteria, mice die
On average, how many DNA uptake sequences are in a genome?
10 - 12 locations on genome
Differences in DNA uptake proteins between G+ And G- bacteria
G+ DNA uptake proteins need to only traverse one membrane
G- need to be more sophisticated, as they need to traverse a double membrane
Can conjugation occur between bacteria of different genera?
Yes
Name of bacterium that receives ssDNA in conjugation
Transconjugant
