RESUMEN
Quorum sensing (QS) is a signaling mechanism governed by bacteria used to converse at inter- and intra-species levels through small self-produced chemicals called N-acylhomoserine lactones (AHLs). Through QS, bacteria regulate and organize the virulence factors' production, including biofilm formation. AHLs can be degraded by an action called quorum quenching (QQ) and hence QQ strategy can effectively be employed to combat biofilm-associated bacterial pathogenesis. The present study aimed to identify novel bacterial species with QQ potential. Screening of Palk Bay marine sediment bacteria for QQ activity ended up with the identification of marine bacterial isolate 28 (MSB-28), which exhibited a profound QQ activity against QS biomarker strain Chromobacterium violaceum ATCC 12472. The isolate MSB-28 was identified as Psychrobacter sp. through 16S-rRNA sequencing. Psychrobacter sp. also demonstrated a pronounced activity in controlling the biofilm formation in different bacteria and biofilm-associated virulence factors' production in P. aeruginosa PAO1. Solvent extraction, heat inactivation, and proteinase K treatment assays clearly evidence the enzymatic nature of the bioactive lead. Furthermore, AHL's lactone ring cleavage was confirmed with experiments including ring closure assay and chromatographic analysis, and thus the AHL-lactonase enzyme production in Psychrobacter sp. To conclude, this is the first report stating the AHL-lactonase mediated QQ activity from marine sediment bacteria Psychrobacter sp. Future work deals with the characterization, purification, and mass cultivation of the purified protein and should pave the way to assessing the feasibility of the identified protein in controlling QS and biofilm-mediated multidrug resistant bacterial infections in mono or multi-species conditions.
RESUMEN
The development of biofilms by microorganisms is conventionally attributed to microbially induced corrosion on stainless steel surfaces and leads to severe consequences in industrial and environmental settings. Since bacterial biofilm formation is regulated by the signal mediated quorum sensing (QS) system, targeting biofilms through QS inhibitors will possibly control biologically induced corrosion on the metal surface. In this study, biofilm formation on 316L stainless steel (SS 316L) immersed in a natural pond water system was effectively inhibited in the presence of the QS inhibitor methyl eugenol, as evidenced through epifluorescence microscopy, confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) analyses. The exopolysaccharide (EPS) and protein extracted from the biofilm formed on the metal surface were found to be reduced by 64% and 60%, respectively, upon exposure to methyl eugenol. In addition, applied electrode potential (open circuit and cathodic) measurements indicated reduced oxygen reduction current at the metal surface that was exposed to methyl eugenol. This inhibitor also enhanced the polarization resistance (Rp) of the SS 316L as indicated by electrochemical impedance spectroscopic (EIS) study.