Adaptation And Response Flashcards
Bact with 2 chromosomes
Brucella
Vibrio
Bact with linear chrom
Bordetella
Genes on bact chrom encode for
Factors req for metabolism
Produce virulence factors
(Virulence determinant genes)
Normal bact chrom appearance
Single circular not enclosed by mem.
Tightly packed in supercoiled state when not repl ir transcribed
Smallest bact chrom
Mycoplasmas approx 1Mb
Larger bact genome
Salm typh
Mycobact bovis both approx 4.5Mb
Burkholderia cepacia approx 9Mb
Intermediate chrom size
Staph and strep approx 2.5 Mb
Larger genome size allow
More complex lifestyle and/or produce more complex structures eg mycobact CW which req more genetic info
Smaller genome size mean
Must rely on many host cell fxs
What allows variation between chromosome size and sequence even within a species?
Mosaic nature of chromosome with large ‘islands’ that arise from bacteriophage integration or uptake and integration of other bact DNA
Pathogenicity islands
Islands encoding numerous virulence-associated factors
What allows easier IDing of aquired regions following sequencing
Altered DNA content especially G/C ratio
Plasmids
Circulat DNA elements 5-100 genes
Replicate autonomously
Products can be important in bact disease eg those encoding virulence factors and antibio res
Potential Phage infection advantages
Phage may carry genes from other bact that confer growth advantage to current host bact. Esp of the genes integrate into the bact chrom
Some are known to carry viruence factors - many toxins transferred via phages
Most pathogenecity islands probably moved between bact by phages
What is success of bact a conseq of
Their capacity to adapt and respond to change
How do they gen variation to survive
By changes made to DNA eg mutations that can be selected for or against (adaptation)
And by having regulation that allows a variety of responses to one stimuli (regulation)
Adaptive genetic changes include
Point mutation (silent/missense/nonsense substitutions)
Deletion/insertion (frame shift)
Inversion, duplication (rearrangement)
Acquisition of new genetic material
Genome alterations induced by
Chem reagents
UV radiation
EC genomic elements
Mechanisms to acquire foreign genes
Transformation
Conjugation
Transduction
Transformation
Uptake of naked EC DNA that may be incorporated into the chrom by recombination or replic independently eg plasmid
Most DNA digested by endonucleases a D against bacteriophages
Conjugation
Some plasmids encode transfer factors which direct conjugation. Filamentous pili prod by donor which adhere to recipient plasmid is duplicated and one strand is transferred via pili to recipient (many antibio res plasmids are conjugative)
Transduction
Process of bact genome transfer via phages
Generalised transduction
Phages randomly acquire and transfer bact genomic sequences
Specialised transduction
Integration (lysogeny) of phage into bact chrom after which adjacent bact sequences to integration site may be packeted by phage to transfer to new host bact following phage induced bact lysis
How can phage sequence become permanent feature in that bact strain
If mutation occurs in key phage replic genes integrated into bact genome but infection by another active phage could rescue defective phage
What drives phage and host bact evolution
Mixing of genetic info between phages to generate multiple variants
What level does regulation occur at
Transcription
Translational
Post-translational
Sensing mechanisms of bact
Activation or repression of gene dep on availability of nutrients
Component signal transduction systems
Quorum sensing
Act/repr of gene sensing mech Fe eg
Fe needed for bact growth so levels closely monitored - low level cause expression of factors to obtain Fe from host (some kill host cell)
How bact sense that they’re in a spec niche
Ion, carbon, nitrogen, O2 tension and temp etc montioring
Component signal transduction
Pass info through bact cell wall and mem following external factor detection.
How is signal in component signal transduction passed
By a phopho-relay system leading to changes in the activity of a DNA binding pro either act or repr certain genes
Quorum sensing
Capacity of bact to monitor particular compounds released by other bact and alter gene expression based on bact cell density.
Quorum sensing uses
When high bact numbers needed to break through barrier
Signal bact presence in spec enviro eg large intestine of GIT cont large no of bact
Molecular koch’s postulates measure
Interrogate Significance of bact genes (suspected as being key in virulence/infection) in the dis process
Molecular koch’s pistukates
Phenotype/genotype investigated should be assoc with pathogenic members of a genus
Spec inact of gene/s assoc with suspected virulence trait should cause measurable pathogenicity/virulence loss
Reversion/allelic replacement of mutated gene should cause restoration of pathogenicity (complementation)
New pacifying method to treat infection
Compounds that combat the expr or act of virulence factors, pacifying pathogen and aiding natural hist D removal
