Synthetic analogs of rhamnolipids modulate structured biofilms formed by rhamnolipid-nonproducing mutant of Pseudomonas aeruginosa.

Rhamnolipids secreted by Pseudomonas aeruginosa are required for the bacteria to form biofilm efficiently and form biofilm with internal structures including pores and channels. In this work, we explore the effect of a class of synthetic analogs of rhamnolipids at controlling (promoting and inhibiting) the biofilm formation activities of a non-rhamnolipid-producing strain - rhlA - of P. aeruginosa. This class of rhamnolipid analogs is known to modulate the swarming motilities of wild-type PAO1 and rhlA mutant, but its effect on biofilm formation of rhlA mutant is unknown. We show that small structural details of these molecules are important for the bioactivities, but do not affect the general physical properties of the molecules. The bioactive synthetic analogs of rhamnolipids promote biofilm formation by rhlA mutant at low concentrations, but inhibit the biofilm formation at high concentrations. To explore the internal structures formed by the biofilms, we first demonstrate that wild-type biofilms are formed with substantial topography (hills and valleys) when the sample is under shaking conditions. Using this observation as a comparison, we found that synthetic analogs of rhamnolipids promoted structured (porous) biofilm of rhlA mutant, at intermediate concentrations between the low ones that promoted biofilm formation and the high ones that inhibited biofilm formation. This study suggests a potential chemical signaling approach to control multiple bacterial activities.