Horizontal Gene Transfer Flashcards
External genetic information is exchanged when
homologous gene recombination occurs, plasmid or bacteriophages take up residence in a new cell
Acinetobacter baumannii
is extremely prone to picking up foreign DNA, has a resistance island (cluster of drug resistant genes)
Transformation is the uptake of
naked DNA fragments from an autolysed cell
what types of cells can acquire naked DNA through transformation
naturally competent cells or forced competent cells
naturally competent cells
their genome encodes the genes for the acquisition of extracellular DNA
forced competent cells
chemical or physical treatments “force” the bacterial cell to acquire extracellular DNA (heat –>ice bath)
Transformation mechanism
naked DNA is accumulated and taken up. RecA replaces homologous sequences of donor DNA with recipient. failure to fit into a replicon (plasmid or chromosome) results in degradation
Organisms that can be transformed
H.flu, Neisseria, Staphylococcus, Streptococcus
Conjugation
horizontal transfer of a plasmid or conjugative transposon by a mechanism which it encodes for
Conjugation and transfer of R factors
mating or establishment of a sexi pili (b/w gram negative cells) followed by ssDNA of R factor is transferred through membrane pore to recipient where is it changed to dsDNA
Transduction
exchange of genetic material mediated by bacteriophages
Two types of bacteriophages
lytic phage and temperate phage
Lytic phage mechanism
generate new virion particles by: binding cell, inserting NA, replication of NA with host machinery, self assembly of gene products into virion, release of virion by lysis or slow release without lysis
Temperate phage mechanism
can act as a lytic phage OR become latent; latency is characterized by repression of lytic genes while residing as a plasmid or within the chromosome
How does latent temperate phage become active?
redepression of genes results in increased expression of genes –> lyssi
lysogenized
bacterial strains with prophage DNA
How does a temperate phage replicate?
replication is in sync with chromosomal DNA replication
How does the bacteria cell lyse when it is time?
the virion particle may encode for a cell wall hydrolase
Generalized (abortive) transduction
occurs with defective phage particles made from sheared donor DNA or plasmid (no VIRAL genome), the donor DNA can be a plasmid, chromosomal fragment that shares homology (RecA), plasmid fragment that shares homology (RecA)
DNA introduced via HGT that is not capable of replication
will be degraded and consumed
Can phages in generalized (abortive) transduction replicate?
NO, there is no viral genome present for viral replication
Lysogenic conversion transduction is mediated by
TEMPERATE BACTERIOPHAGES only
Lysogenic conversion is
acquisition of a new phenotypic trait due to a latent temperate prophage
Lysogenic conversion __________ require activation of the temperate virus genome
DOES NOT
Lysogenic conversion is the introduction of a gene coding for
exotoxin, exotoxin gene expression is regulated separately from viral genes, does not affect latency, and can change the phenotype of the bacterial cell
Generalized transduction of drug resistance (genera)
staphylococcus, streptococcus, others
Lysogenic conversion transduction of exotoxin production (genera)
corynebacterium diphtheria, streptococcus pyrogenes, clostridium botulinum, staphylococcus aureus
Phage typing
classifying bacteria based on which strains of bacteriophages are capable of infecting them
1 bacteria may be infected by ______ phages
many
1 phage may infect _________ bacteria
1 strain of
