Evolution is a gradual process in which something transforms into a better/more complex form. In biology, it’s survival of the fittest. The more efficient a cell is within its environment, the greater it’s chance of survival. The importance of finely-tuned functioning biochemical networks, regulatory mechanisms, and cellular components is immense for all living organisms’ survival. As new adverse environments inevitably arise, cells must overcome them with as little alteration to their pre-existing successful metabolic systems as possible, in order to facilitate evolution. Many notable studies suggest the most efficient process to continually evolve and overcome stressful conditions is to induce specific feedback mechanisms that mutate the genes derepressed by starvation or other environmental stressors. Specifically, stress-directed mutagenesis (SDM) results in an increase in mutation rates in genes that must mutate in order to lessen the stress. The resulting advantageous mutants provide appropriate variants which can be selected for without causing excessive or irreparable damage to the genome.A very common lab study involves cells incorporated into an environment lacking glucose. Under such severe conditions numerous genes are derepressed and activated, for example, two E.coli genes that function in metabolism of guanosine 5',3'-polyphosphates (ppGpp), relA and spotT. This instigates a cascade of derepression of starvation-responsive genes such as those involved with protecting cells from additional stressors like heat and oxidative damage. In addition to the widespread gene-activation, a 30-fold increase in mutation rate also transpires, to potentially provide beneficial mutations and increased fitness. The target genes for this SDM are those derepressed under stress. That's feedback!
Ashleigh Lazzarini – 41206654
Further Information & related articles:
Selection, adaptation, and bacterial operons [click here]
Stationary phase mutagenesis: mechanisms that accelerate adaptation of microbial populations under environmental stress. [click here]
Primary reference;
Wright,B. 2004, ‘Stress-directed adaptive mutations and evolution.’ MicroReview. Molecular Microbiology 52 (3), 643–650. [click here]
Seconday reference;
Functional analysis of a relA/spoT gene homolog from Streptococcus equisimilis. [click here]
