Flavonoids Suppress Pseudomonas aeruginosa Virulence through Allosteric Inhibition of Quorum-sensing Receptors

Abstract

Quorum sensing is a process of cell-cell communication that bacteria use to regulate collective behaviors. Quorum sensing depends on the production, detection, and group-wide response to extracellular signal molecules called autoinducers. In many bacterial species, quorum sensing controls virulence factor production. Thus, disrupting quorum sensing is considered a promising strategy to combat bacterial pathogenicity. Several members of a family of naturally produced plant metabolites called flavonoids inhibit biofilm formation by an unknown mechanism. Here, we explore this family of molecules further, and we demonstrate that flavonoids specifically inhibit quorum sensing via antagonism of the autoinducer-binding receptors, LasR and RhlR. Structure-activity relationship analyses demonstrate that the presence of two hydroxyl moieties in the flavone A-ring backbone are essential for potent inhibition of LasR/RhlR. Biochemical analyses reveal that the flavonoids function non-competitively to prevent LasR/RhlR DNA binding. Administration of the flavonoids to alters transcription of quorum sensing-controlled target promoters and suppresses virulence factor production, confirming their potential as anti-infectives that do not function by traditional bacteriocidal or bacteriostatic mechanisms.

Inhibitors of Bacterial Swarming Behavior

“…Flavonoids were found to be allosteric inhibitors of these quorum‐sensing receptors and prevented their binding as transcription factors to DNA. Two of the most active compounds, phloretin ( 9 ) and 7,8‐dihydroxyflavone were finally tested on quorum‐sensing‐controlled behaviors of P. aeruginosa and completely abrogated swarming at 100 μ m . The flavonoid quercetin ( 8 ) considerably reduced swarming motility of P. aeruginosa and Yersinia enterocolitica at 132 μ m .…”

“…Twoo ft he most active compounds, phloretin (9)a nd 7,8-dihydroxyflavone weref inally tested on quorum-sensing-controlled behaviors of P. aeruginosa and completely abrogated swarming at 100 mm. [41] The flavonoid quercetin (8)c onsiderably reduceds warming motility of P. aeruginosa and Yersinia enterocolitica at 132 mm. [42] In Proteusv ulgaris,5 0mm of quercetin (8)n ot only inhibited the production of N-octanoyl-l-homoserine lactone (C8-HSL) by 81 %a nd caused an almost equal reduction in swarming area,b ut also supposedly interfered withs warming by binding to the sigma factor FliA which regulates flagellar operons (Figure 2, left).…”

Mechanism underlying autoinducer recognition in theVibrio choleraeDPO-VqmA quorum-sensing pathway

“…For each system being tested, ∆tdh E. coli harboring one plasmid encoding the arabinose-inducible receptor-transcription factor (VqmA, LasR, or VqmAPhage) and a second plasmid containing the cognate target promoter (PvqmR, PlasB, or Pqtip, respectively) fused to lux (10,38) was used. In parallel, a control strain for each system was used that carried the reporter plasmid alone (PvqmR-lux, PlasB-lux, or Pqtiplux).…”

Effect of Capsicum Frutescens Extract, Capsaicin, and Luteolin on Quorum Sensing Regulated Phenotypes

“…Paczkowski et al. () elucidated the QS inhibition mechanism of nine flavonoids, showing an allosteric interaction over LasR and RhlR in P. aeruginosa . These authors did not test luteolin.…”

“…Violacein, a purple pigment produced by Chromobacterium violaceum , is also regulated by QS. These two bacteria are used as model organisms in many studies (Morohoshi, Kato, Fukamachi, Kato, & Ikeda, ; Paczkowski et al., ; Rasamiravaka, Labtani, Duez, & El Jaziri, ).…”