Editors' ChoiceBiofilms

Polyamines determine dispersal

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Science Signaling  04 May 2021:
Vol. 14, Issue 681, eabj2318
DOI: 10.1126/scisignal.abj2318

Monitoring of environmental polyamines controls the dispersal of Vibrio cholerae biofilms.

Although living in biofilms enables bacteria to collectively exploit resources and resist existential threats, cells must be able to leave biofilms and disperse to new locations. Bridges and Bassler identified polyamines as one of the cues that controls dispersal from Vibrio cholerae biofilms. Mutations in the polyamine sensor MbaA or the polyamine importer PotD1 reduced dispersal and increased cytoplasmic c-di-GMP, a second messenger that promotes biofilm formation and suppresses motility. The polyamine spermidine reduced c-di-GMP and promoted dispersal, whereas norspermidine, an unusual polyamine produced by Vibrio species, increased c-di-GMP and inhibited dispersal. MbaA is a transmembrane protein with a periplasmic polyamine sensor domain and cytoplasmic diguanylate cyclase and phosphodiesterase domains, indicating that it has the potential to both synthesize and degrade c-di-GMP in response to polyamines. Both catalytic domains were required for polyamine-mediated control of dispersal, with high periplasmic norspermidine favoring c-di-GMP biosynthesis and the presence of spermidine or low amounts of norspermidine favoring c-di-GMP degradation. Although the amounts of spermidine and norspermidine in the cytoplasm did not affect dispersal, cells released large amounts of norspermidine into the environment at high cell density. PotD1 contributed to dispersal by controlling the equilibrium between norspermidine release and reimport from the periplasm. Why environmental polyamines are important for the decision to remain in the biofilm or disperse is not clear, but it may be that the presence of norspermidine promotes biofilm maintenance when conditions are generally favorable for Vibrio, whereas large amounts of spermidine, which is produced by all bacterial species, promotes dispersal to reduce competition.

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