Discussion
Which one of the following molecules is the master regulator of the planktonic-surface transition in Pseudomonas aeruginosa during biofilm formation?
Answer: B
The master regulator is cyclic dimeric guanosine monophosphate (c-di-GMP).
In Pseudomonas aeruginosa c-di-GMP is made by diguanylate cyclases and broken down by phosphodiesterases. A high level switches the cell from swimming (planktonic) to the sessile state: flagellar motility is turned down and the production of exopolysaccharides such as Pel and Psl, which build the biofilm matrix, is turned up. A low level favours dispersal.
Cyclic thiolactone peptides are quorum-sensing signals of Gram-positive staphylococci, cyclic triadenylate is a second messenger of bacterial antiphage defence systems, and cycloheximide is an antibiotic that blocks eukaryotic protein synthesis. None controls this transition.
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