Part B - What role does quorum sensing play in toxin secretion? One possible exp
ID: 32688 • Letter: P
Question
Part B - What role does quorum sensing play in toxin secretion?
One possible explanation for the sudden threshold effect for toxin secretion seen in S. aureus cultures is that this bacteria regulates toxin secretion by quorum sensing. Quorum sensing is a way that bacteria can sense when their population size reaches a particular density, and then do something different in response. In other words, quorum sensing allows an entire population of bacteria to carry out coordinated activity.
Individual bacteria secrete signaling molecules that other individuals can detect. As the population grows, the concentration of the signaling molecule in the environment increases. Once the concentration of the signaling molecule reaches a threshold level, as detected by receptors on the bacterias surface, signal transduction pathways in the bacteria are triggered that induce expression of a target gene. The target gene may code for a protein involved in bioluminescence, the formation of a biofilm, or toxin production. Quorum sensing ensures that individual bacteria dont express a gene until every individual in the population simultaneously expresses that same gene.
To test the hypothesis that toxin secretion in S. aureus is dependent on quorum sensing, you examine mutants that are known to block two separate quorum-sensing pathways: the agr pathway and the TRAP pathway. You use completely normal (wild-type) cells as a control. You also decide to examine the ztr- mutant as an additional control, since this mutant is known not to be involved in quorum sensing, and you wish to test for an effect specific to quorum-sensing mutations. For each mutant, you grow cultures to a standardized high density, measure the amount of toxin they produce, and compare them to the wild-type control cells.
From these data, you propose a model of how S. aureus changes from a harmless bacterium on the skin to a serious pathogen inside a wound.
Arrange the steps in order to complete your model. Not all labels will be used. See Hint 1 for help getting started.
Explanation / Answer
1. S .aureus grow at low density on skin surface.
2. S .aureus enter tissue through a wound.
3. S .aureus grow to high density inside tissue.
4. S. aureus sense quorum through both the agr and TRAP pathways.
5. S .aureus secrete toxin.