Adaptation And Response Flashcards
(37 cards)
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