Bacterial Evolution and Genetics Flashcards
How are bacterial species identified?
16S rRNA sequencing.
What are the 2 levels of bacteria identification below species level?
Strain level and isolate level.
What is an isolate?
A culture from an infection.
What is a strain?
A genetic variant of a microorganism.
What are the 3 strain typing techniques and their average nucleotide identity (ANI)?
DNA-DNA hybridisation (>70%)
16S rRNA gene sequencing (>97%)
Whole genome sequencing (>95%)
Define average nucleotide identity (ANI).
A measure of nucleotide-level genomic similarity between the coding regions of two genomes.
Define epidemiology.
Identification and tracking of disease and infection.
Why is it important to study bacteria below species level?
Some strains may cause different diseases or may be more transmissible or deadly.
What are the T.RA.D. criteria?
Typeability, reproducibility, accuracy and discriminatory power. All features desired in strain typing.
What is typeability?
The number of isolates that can be identified.
What is the range in G+C content for bacterial genomes?
20-75%
What are bacterial chromosomes like?
1 double-stranded circular DNA chromosome. Can occasionally be linear.
How is bacterial DNA organised?
Almost all coding material is on 1 gene (around 1kb). Bacteria possess a core + accessory genome.
What are the features of the accessory genome?
Non-essential genes.
Foreign DNA.
Cause of rapid evolutionary change and diversity with and between species.
What are the features of the core genome?
Essential genes.
Stable G+C content.
Shared within species.
Slow evolution.
What are the 2 drivers of bacterial genome evolution?
Horizontal gene transfer (HGT) and mutation/recombination.
Define horizontal gene transfer (HGT).
Transfer of genetic material between organisms not in a parent-offspring relationship.
Give 3 examples of horizontal gene transfer (HGT.
Plasmids, bacteriophages and transposable elements (‘jumping genes’).
What is a genomic island?
Large DMA regions often integrated into the genome that are not present in all strains of the same species.
What are some examples of advantageous accessory genes?
Pathogenecity.
Fitness.
Resistance.
Symbiosis.
Define additive evolution.
Gene acquisition, duplication and rearrangement in the accessory genome.
Define reductive evolution.
Deletion, inactivation and pseudogene formation in the core genome.
Describe a bacterial plasmid.
Circular, self-replicating DNA molecule. Inherited through cell division. Encodes machinery for conjugation.
Describe a bacteriophage.
Bacterial viruses that phage genetic material injected into cell. Integrates into genome (lysogeny).
Describe a transposable element.
Insertion sequences of 0.7-2.5kb or transposons of 2.5-60kb. A DNA sequence that change its position within a genome.
What enzyme binds to the end of a transposon?
Transposase.
Define transformation.
The incorporation of foreign DNA into the genome.
Define transduction.
Bacteriophage-mediated DNA transfer (virus transfers genetic material).
Define conjugation.
The transfer of DNA via cell-to-cell contact.
