Friday, May 19, 2006

Signals - Red, Amber, and Green.

A practice long assessment question.

Take about 30 minutes to give an answer, devoting about equal time to each part.

Specialised signaling compounds are very important in enabling bacterial cells to adapt and survive in different environments, and to coordinate cell responses.

Such bacterially made chemicals include compounds that can be involved in either inter-cellular communication outside the cell, or intra-cellular communication within the cell.

  1. Give examples of two structurally distinct intercellular (ie extra-cellular) signaling chemicals used by bacteria, and explain what you know about their functional roles and mechanisms of action.
  2. Give examples of two structurally distinct intracellular signaling chemicals used by bacteria, and explain what you know about their functional roles and mechanisms of action.
  3. Explain how a signaling pathway can activate expression of a set of unlinked genes, and give one specific example of a set of bacterial genes whose activity is triggered by an extra-cellular signal.


Anonymous microbialcells said...

There were two I recall
Nature. 2000 Oct 12;407(6805):762-4.
Quorum-sensing signals indicate that cystic fibrosis lungs are infected with
bacterial biofilms.
Singh PK, Schaefer AL, Parsek MR, Moninger TO, Welsh MJ, Greenberg EP.

The bacterium Pseudomonas aeruginosa permanently colonizes cystic fibrosis lungs
despite aggressive antibiotic treatment. This suggests that P. aeruginosa might
exist as biofilms--structured communities of bacteria encased in a self-produced
polymeric matrix--in the cystic fibrosis lung. Consistent with this hypothesis,
microscopy of cystic fibrosis sputum shows that P. aeruginosa are in
biofilm-like structures. P. aeruginosa uses extracellular quorum-sensing signals
(extracellular chemical signals that cue cell-density-dependent gene expression)
to coordinate biofilm formation. Here we found that cystic fibrosis sputum
produces the two principal P. aeruginosa quorum-sensing signals; however, the
relative abundance of these signals was opposite to that of the standard P.
aeruginosa strain PAO1 in laboratory broth culture. When P. aeruginosa sputum
isolates were grown in broth, some showed quorum-sensing signal ratios like
those of the laboratory strain. When we grew these isolates and PAO1 in a
laboratory biofilm model, the signal ratios were like those in cystic fibrosis
sputum. Our data support the hypothesis that P. aeruginosa are in a biofilm in
cystic fibrosis sputum. Moreover, quorum-sensing signal profiling of specific P.
aeruginosa strains may serve as a biomarker in screens to identify agents that
interfere with biofilm development.

Science. 2006 Feb 24;311(5764):1113-6.
Bacterial small-molecule signaling pathways.
Camilli A, Bassler BL.

Bacteria use diverse small molecules for extra- and intracellular signaling.
They scan small-molecule mixtures to access information about both their
extracellular environment and their intracellular physiological status, and
based on this information, they continuously interpret their circumstances and
react rapidly to changes. Bacteria must integrate extra- and intracellular
signaling information to mount appropriate responses to changes in their
environment. We review recent research into two fundamental bacterial
small-molecule signaling pathways: extracellular quorum-sensing signaling and
intracellular cyclic dinucleotide signaling. We suggest how these two pathways
may converge to control complex processes including multicellularity, biofilm
formation, and virulence. We also outline new questions that have arisen from
recent studies in these fields.

May 21, 2006 10:33 pm  

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