Exploration of Ligand-Receptor Binding and Mechanisms for Alginate Reduction and Phenotype Reversion by Mucoid Pseudomonas aeruginosa.

Burns, Felicia N; Alila, Mercy A; Zheng, Hewen; Patil, Pankaj D; Ibanez, Arizza Chiara S; Luk, Yan-Yeung

Bacteria in general can develop a wide range of phenotypes under different conditions and external stresses. The phenotypes that reside in biofilm, overproduce exopolymers, and show increased motility often exhibit drug-tolerance and drug-persistence. In this work, we describe a class of small molecules that delay and inhibit the overproduction of alginate by a non-swarming mucoid Pseudomonas aeruginosa . Among these molecules, selected benzophenone-derived alkyl disaccharides cause the mucoid bacteria to swarm on hydrated soft agar gel and revert the mucoid to non-mucoid phenotype. The sessile (biofilm) and motile (swarming) phenotypes are controlled by opposing signaling pathways with high and low intracellular levels of bis-(3',5')-cyclic diguanosine monophosphate (cdG), respectively. As our molecules control multiple of these phenotypes, we hypothesized and explored a protein receptor, pilin of the pili appendages, that are consistent with controlling these bioactivities and signaling pathways. To test this binding hypothesis, we developed a bacterial motility enabled binding assay that utilizes the interfacial properties of hydrated gels and bacterial motility to conduct label-free ligand-receptor binding studies. The structure activity correlation and the receptor identification reveal a plausible mechanism for reverting mucoid to nonmucoid phenotypes by binding pili appendages with ligands capable of sequestering and neutralizing reactive oxygen species.