Effect of adding exogenous acyl homoserine lactone signal to Pseudomonas aeruginosa premature culture and prediction of signal binding domain in Rhamnolipids RhlA enzyme

The hierarchy of the quorum-sensing system plays a crucial role in Pseudomonas (P.) aeruginosa virulence and the production of important industrial bacterial products like rhamnolipids and proteases. In this study, the effect of adding exogenous acyl-homoserine lactone synthetic signal to the premature culture of P. aeruginosa on the production of protease and rhamnolipids was investigated. At the early exponential phase, induction of rhamnolipid production showed a more rapid response than protease production. Prediction of the 3D structure of the acyltransferase RhlA enzyme, which is the first key enzyme in rhamnolipid synthesis, was then done using the I-Tasser program to investigate the possible protein structure that might influence the response to N-acyl-homoserine lactone (AHL) presence. With a good C-score, 3D modeling showed RhlA to have AHL binding pocket where ten ligand binding site residues were elucidated in the protein. Multiple sequence alignment revealed low homology with LuxR proteins. Although conserved residues were depicted from the alignment, they were different from the ligand-binding residues suggesting that AHL binds to RhlA with a different mechanism than LuxR proteins. After further bioinformatics analysis, we found that RhlA binds to AHL in a mechanism similar to the lactonase enzyme. In conclusion, the in silico domain and protein alignment analysis revealed an AHL binding site in the RhlA enzyme protein structure.