18. Microbial Genetics II Flashcards
generalized transduction:
bacteria chromosome is accidently packaged into a viral capsid
- any gene of the host bacterium can be transferred to recipient and doesn’t require lysogeny
specialized transduction:
specific genes near the attachment sites of a lysogenic phage in the host chromosome are transferred
-depends on initial development of lysogeny followed by inaccurate excision
abortive transduction:
the transferred DNA is not integrated but often is able to temporarily survive and express
CRISPR
clustered regularly interspaced short palindromic repeats- a bacterial immune response to phages, like a DNA antibody
describe the two processes of bacterial conjugation
- a pilus forms and perhaps transfers DNA or brings the two cells in close contact with one another to enable transfer
- a chemoattractant gradient brings to the two cells into close proximity
incompatibility groups
plasmids are selected based on these groups such that only one version exists in a population
-this is often used for taxonomy purposes
the __ is the plasmid origin used in transfer, the __ is the plasmid origin used in normal replication
oriT, oriV
how does a plasmid get integrated into the bacterial chromosome?
insertion sequences on the plasmid has counterparts on the bacterial chromosome, leading to homologous recombination
Hfr plasmid
a plasmid + bacterial chromosome
H’ plasmid
the splicing of the integrated plasmid is sloppy, leading to the formation of a new plasmid
how does plasmid integration result in the transfer of a different sequence of bacterial chromosome?
a portion of the plasmid begins as the lead sequence, but bacterial DNA is transferred behind it (instead of the plasma portion)
what are the mechanisms of plasmid specified resistance?
- efflux pumps
- degrade enzyme
- modify enzyme
- modification of the antibiotic target
- bypass (specifies a new enzyme that isn’t affected by the antibiotic but does the same thing)
what are the mechanisms of chromosomal mediated resistance?
-target alteration through mutation
how are transposable elements involved in the transfer of antibiotic resistance?
a transposable element carrying antibiotic resistant elements can pick up and move from the chromosome to a plasmid
what is a method that a plasmid can maintain itself in a population?
some plasmids produce a toxin and an anti-toxin-if a bacteria tries to lose a plasmid, the anti-toxin has a shorter half life, allowing the toxin to kill the cell
insertion sequences
don’t specify any gene product, just the transposase
-contains inverted repeats at the ends
composite transposon
a central sequence bounded by an insertion sequence
TnA like elements
not bound to an associated insertion sequence, encodes resistance to penicillin and similar antibiotics (beta lactamase)
gene cassettes
a gene and a counterpart att site, confers antibiotic resistance
-free in the environment
integron structure
contain an integrase and an att site, as well as a promoter
how do chromosomal integrons work?
- during normal conditions, there is neutral drift because mutations don’t affect the cell function
- when a stress occurs, it turns on the integrase leading to a shuffling of the genes and promoters of the cassettes such that you might get something useful to the bacteria
transposons must be associated with a:
replicon (a plasmid chromosome phage), they aren’t capable of self-replication within a cell
selective/developed resistance
all strains of an organism are initially sensitive to the challenge, over time a percentage of the strains develop resistance
what are the two types of resistance and what is the significance?
plasmid and chromosomal
- plasmid resistance can be transferred horizontally (rapid spread)
- chromosomal resistance is slower and only transferred to offspring
