Bacterial Genetics Flashcards
and posters
Bacterial genetics are increasingly being used in veterinary - what are these uses?
- Detection e.g., PCR
- identification e.g., whole genome sequencing
- epidemiology e.g., identify variants of concern, disease transmission pathways
- determining antibiotic resistance and presence of virulence factors
What is the nucleoid?
- a bacterial chromosome which is one large circular molecule (haploid)
How much longer is a nucleoid compared to a bacterial cell and what is its structure?
- 1000 times longer than a bacterial cell and extensively folded to form a dense body that cam be visualised by electron microscopy
How many base pairs does a nucleoid have?
- 0.8 - 0.4 x 10’6
One copy of what is given to the daughter cell?
- nucleoid
What is a plasmid?
- A plasmid is a large circular molecule of double-stranded DNA that replicate autonomously from the chromosome
What does a plasmid encode for?
- Encodes genes for self-transmissibility
What do virulence factors help bacteria to do?
- help bacteria to infect humans, animals and plants by a variety of mechanisms
What are way virulence factors can help bacteria?
- some are toxins that damage or kill animal cells
- others help bacteria attach to and invade animal cells
- others protect bacteria against retaliation by the immune system
What are two examples of virulence plasmids?
- Anthrax - bacillus anthracis contains pXO1 plasmid which encodes the bacterial toxin components and pXO2 plasmid which encodes the capsule which enables the bacteria to evade the immune system
- E.coli O157:H7 - possesses the plasmid pO157 that encodes a periplasmic catalase that provides additional oxidative protection against the host defence mechanism . the shigella-like toxin is encoded by a prophage
What is a mutation?
- an alteration of the nucleotide sequence from the wild-type
What is a phenotypic adaptation?
- metabolic adjustment in the whole population to environmental conditions
What is genetic variation?
- is the presence of differences in sequences of genes between individual organisms of a species
What does genetic variation enable?
- enables natural selection, one of the primary forces driving the evolution of life
What does genetic variation within a group enable?
- enables some organisms to survive better than others in the environment in which they live
- organism of even a small population can differ in terms of how well suited they are from life in a certain environment
Genetic variation within a species can result from a few different sources - what are these?
- mutations, the changes in the sequences of the genes un DNA
- Gene transfer
- the movement of genes between different groups of organisms
What is mycobacterium bovis and where does it reside?
- the causative organism of bovine tuberculosis
- resides within granulomas of the lung and draining lymph nodes with very little access to other organisms
Mycobacterium bovis has little to no opportunity for gene transfer so how is genetic variation generated?
- generated by point mutation, gene duplication and indels (insertion or deletion of bases in the genome)
Where do E.coil and Salmonella reside?
- reside in the intestine which are rich in bacteria (up to 5 x10’10 per gram)
How do E.coli and salmonella approach genetic variation?
- in this environment gene transfer mechanisms are commonly used to generate genetic variation and to rapidly disseminate advantageous genetic info between organisms
What is transduction?
- injection of DNA into a bacterium by a phage
What is conjugation?
- plasmid in a donor bacterium is transferred though a pilus into a recipient bacterium
- plasmid may integrate into the chromosome or remain in the cytoplasm
- plasmid may be transferred between cytoplasmic and chromosomal locations
- plasmid may exchange insertion sequences or transposons with other plasmids or the chromosome
What is transformation?
- uptake of naked DNA from the environment
Gene transfer in bacteria can be what?
- conjugated (plasmid-mediated)
- transduction (phage mediated)
- transformation (uptake of naked DNA)
What is the Fertility factor (F factor)?
- is a conjugative plasmid transferred from cell to cell by conjugation
- is an episome = genetic element that can inset into chromosome or replicate as circular plasmid
What is the F plasmid?
- is a low-copy-number plasmid
-100kb in length - present in 1-2 copies per cell
How does the F plasmid replicate?
- replicates once per cell cycle and segregate to both daughter cells in cell division
In bacterial mating, conjugation and DNA transferer what is the direction?
- unidirectional
What is bacterial transformation?
- the process of genetic alteration by pure DNA
During bacterial transformation how do recipient cells acquire genes?
- from DNA outside the cell
How is DNA acquired in bacterial transformation?
- may be natural
- chemically
- electrically induced
In transformation what happens after DNA is taken up by the cell?
- often recombines with genes in bacterial chromosome
What can transformation alter?
- may alter phenotype of recipient cells
How are genes located close together transferred?
- are often transferred as a unit to recipient cell = co transformation
How are genes that are far apart transferred?
- less likely to be transferred together
What are transposable elements
- DNA sequences that cannot self-replicate but can jump from one position to another or form one DNA molecule to another
Bacteria contain a wide variety of what?
- transposable elements
The smallest and simplest insertion sequences or IS elements, which are 1-3kb in length contain what?
- contain inverted repeat sequences of DNA and encode the transposase protein required from transposition and one or more additional proteins that regulate the rate of transposition
How do transposable elements enhance genetic diversity and evolution?
- by causing deletions and genetic rearrangement within replicons
What is a transposon?
- is where other transposable elements in bacteria contain one or more genes unrelated to transposition that can be mobilised along with transposable elements
What can transposons do?
- insert into plasmids which can be transferred to recipient cells by conjugation
How are transposable elements flanked?
- inverted repeats
- often contain multiple antibiotic resistance genes
Restriction and modification systems can be used as what?
- defence mechanisms that bacteria use to prevent infection by foreign DNA (such as viruses)
What two enzymes do modification and restriction systems consist of?
- restriction endonuclease
- methylase (or methyltransferase)
What is restriction?
= cutting (site-specific endonuclease activity)
- is a means by which bacteria evade viruses or other incoming DNA
What is modification?
= protection (site-specific endonuclease activity)
- modification is the protection of the organisms own DNA
What does restriction endonucleases recognise?
- specific sequences on the incoming DNA and cut them
Methylases methylate has the same sequence in the bacterial genome to do what?
- to prevent self-destruction (cutting) of its own DNA
Adenosine or cytosine methylation are mediated by what?
- restriction modification systems of many bacteria
