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Module: BIOM – 1009

Lecturer: Dr Bonab

Date: 17/11/16

Microbial Genetic Function
o

Bacteria are able to shuffle their genes
...
They will then go
on to start another cycle with another bacterium
 Lysogenic cycle
o In this cycle, after the phage has injected the host bacteria, the DNA does
combine with the new DNA
 This makes the new genome a prophage
o The bacteria will continue to divide normally by binary fission
 It will also replicate the prophage
o Occasionally the prophage my excise from the chromosome, entering
the lytic cycle



Transduction can also be sorted into two types:
 Generalised
o After the phage infects the bacterium an enzyme, DNase, cleaves the DNA
contained in the phage so it can be properly enclosed in viral particles
o Most of the time, the new phages are non-transducing
 Occasionally, the new phage may pick up some/all of the host
genome and so will infect another bacterium with the host
chromosomes
 Specialised
o The DNA from both the host and virus gets incorporated together into a
prophage
 This is usually placed at a precise location on the chromosome
o When the viral DNA becomes excised, it usually excises part of the
bacterial genome with it
o When the new phage infects a bacterium, it will contain part of the host
genome (this could be antibiotic resistance)



Conjugation
 Conjugation requires direct contact between the donor and recipient cells
 It is an important mechanism in both Gram-positive and Gram-negative bacteria
o In Gram-positive bacteria, the cell walls of each cell stick together using a
conjugation pilus (located on the F plasmid)
o In Gram-negative bacteria, the process is much more complicated
 The process is as follows (see below):
 The donor bacterium produces a pilus and attaches to the recipient bacterium
 DNA helicase then unzips one strand of the plasmid which travels across the
pilus to the recipient
o This begins at a specific site known as the origin of transfer
o The information on this plasmid contains the information for pili
synthesis
 Both the donor and recipient will then synthesise a complementary strand to the
plasmid, allowing each organism to have one full copy
 The recipient can now become a donor, and so can conjugate with other cells
 Plasmids are the most common vectors used in genetic transformation, they contain
three key elements (see bottom):
 The origin of replication
 A selectable marker gene
o Such as antibiotic resistance
 A cloning site
o An area within the plasmid where new DNA is inserted



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