Bacterial Genetics Flashcards
(19 cards)
What is Horizonal Gene Transfer (HGT)?
Movement of genetic information between organisms
Distinguished from transmission of genetic material during reproduction (known as vertical gene transfer, VGT)
In 1928, what did Griffith observe in Streptococcus pneumoniae?
Identified Transforming principle (transferred components of killed smooth cell -> rough cell to change rough cell’s behaviour)
Can transformation occur if DNA is not present?
No, therefore DNA must be hereditary material
What is transduction in bacterial genetics?
Transfer of DNA between bacterial cells where bacteriophage is the transfer agent
What are the 2 types of transduction events?
1) Specialised transduction
2) Generalised transduction
What are bacteriophages specifically designed to infect?
1 species (or even greater specificity to sub-species)
Once attached, they inject their DNA and use host ‘machinery’
What is specialised transduction?
Where excision of viral DNA from host DNA takes gene adjacent to site of lysogeny + incorporates them into viral genome
Means that the bacteriophage is transferring/transducing genes between competent cells
What is generalised transduction?
Any gene in a host genome can be transduced into phage genome - not just those adjacent to site of lysogeny
This process can be used for biotech purposes - used for making chromosomal alterations to target host species
What is the difference between Lytic and Lysogenic bacteriophages?
Lytic - bacteriophages begin to kill host bacterial cell upon entry
Lysogenic - bacteriophages do not begin to kill host bacterial cell upon entry
What do lysogenic bacteriophages do?
Can become integrated in host bacterial chromosome (known as prophages)
Once there, can be dormant until excised through recombination event - if this happens they will re-circularise in cytoplasm and initiate a lytic cycle (kills host)
What happens in the process of conjugation in bacterial genetics?
Some species possess a plasmid (fertility factor) allowing them to transfer DNA to cells of same species
Transfer is unidirectional from donor (designated F+) to recipient (F-)
Facilitated by use of pili
What do F+ cell pili do?
Attaches to F- cell of same species, forming physical bridge between cytoplasm of 2 cells
F+ cells uses its ribosomes to copy plasmid and copy is transferred through pilus to F- cell
What happen when an F- cell obtains a copy of F factor?
It becomes F+
Both cells synthesise a complementary DNA strand
Both F+ males then separate
What is plasmid compatability?
To be passed to subsequent generations, they must be able to be stably inherited
Plasmids that can’t be copied are said to be incompatible (non-stable inheritance)
How is plasmid incompatibility defined as?
Refers to inability of 2 plasmids to coexist stably over a no. of generation in same bacterial cell line
Closely related plasmids tend to be incompatible, while distantly related plasmids tend to be compatible
What are incompatibility groups abbreviated as?
Inc groups
Independently classified as 3 different genera (Enterobacteriaceae, Pseudomonas, Staphylococcus)
What is conjugative plasmid transfer?
Plasmids spread DNA among different bacteria
What happens to Gram- species in conjugative plasmid transfer?
ds plasmid DNA cleaved at oriT site by relaxase protein - covalently binds to origin of transfer (oriT) DNA
Resultant DNA-protein complex is transported to recipient cell by T4SS
ssDNA is transferred into recipient cell by T4CP
What 2 methods can Gram+ bacteria use to transfer plasmids?
1) A ss of plasmid DNA is transported via T4SS
2) Plasmids of the order Actinomycetales have conjugative systems similar to segregation of chromosomal DNA during bacetrial cell division + sporulation. Translocation of dsDNA to recipient DNA mediated by FtsK-homologous protein
