Production of acylated homoserine lactone by a novel marine strain of Proteus vulgaris and inhibition of its swarming by phytochemicals

Abstract

A marine strain of Proteus vulgaris capable of activating multiple acylated homoserine lactone (AHL)-based reporter cultures was isolated. The cognate signal molecule was characterized as octanoyl homoserine lactone (OHL) and its production was observed to be growth dependent, with maximum production (5.675 mg l "1 ) at 24 h growth. The strain exhibited swarming, but its motility was not affected upon addition of pure OHL or culture supernatant. Phytochemicals such as quercitin and berberine chloride inhibited OHL production and reduced swarming. FliA, the predominantly upregulated protein during swarming, was considered as a possible target for these inhibitors, and docking of the two most active and two least active inhibitors to this protein suggested preferential binding of the former set of compounds. Apart from adding new evidence to AHL production in Proteus vulgaris, active inhibitors shortlisted from this study could help in identifying lead compounds to act against this opportunistic pathogen of the respiratory and gastrointestinal tract.

Inhibitors of Bacterial Swarming Behavior

“…[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). [43] Av irtual docking-approach against the AHL receptor LasR identified salicylic acid and chlorzoxazonea sp otential quorum-sensing inhibitors of P. aeruginosa which was confirmed biochemically through LasR and additionally RhlR and resultedi ni nhibition of swarming of S. liquefaciens in the millimolar range. [44] Also complex natural-product mixtures and ex-tracts have been found to exhibit quorum-sensingi nhibiting activities affecting swarming behavior.F or example, propolisbee glue-antagonized AHL-based quorum-sensing signaling in RhlR-and LasR-dependent reporter strains and reduced swarming activity of P. aeruginosa.…”

“…The flavonoid quercetin ( 8 ) considerably reduced swarming motility of P. aeruginosa and Yersinia enterocolitica at 132 μ m . In Proteus vulgaris , 50 μ m of quercetin ( 8 ) not only inhibited the production of N ‐octanoyl‐ l ‐homoserine lactone (C8‐HSL) by 81 % and caused an almost equal reduction in swarming area, but also supposedly interfered with swarming by binding to the sigma factor FliA which regulates flagellar operons (Figure , left) . A virtual docking‐approach against the AHL receptor LasR identified salicylic acid and chlorzoxazone as potential quorum‐sensing inhibitors of P. aeruginosa which was confirmed biochemically through LasR and additionally RhlR and resulted in inhibition of swarming of S. liquefaciens in the millimolar range .…”