The LuxR family protein SpnR functions as a negative regulator of N‐acylhomoserine lactone‐dependent quorum sensing in Serratia marcescens

Abstract

SummarySerratia marcescens SS-1 produces at least four N -acylhomoserine lactones (AHLs) which were identified using high-resolution mass spectrometry and chemical synthesis, as N-(3-oxohexanoyl) homoserine lactone (3-oxo-C6-HSL), N -hexanoyl-(C6-HSL), N -heptanoyl (C7-HSL) and N -octanoyl-(C8-HSL) homoserine lactone. These AHLs are synthesized via the LuxI homologue SpnI, and regulate via the LuxR homologue SpnR, the production of the red pigment, prodigiosin, the nuclease, NucA, and a biosurfactant which facilitates surface translocation. spnR overexpression and spnR gene deletion show that SpnR, in contrast to most LuxR homologues, acts as a negative regulator. spnI overexpression, the provision of exogenous AHLs and spnI gene deletion suggest that SpnR is de-repressed by 3-oxo-C6-HSL. In addition, long chain AHLs antagonize the biosurfactantmediated surface translocation of S. marcescens SS-1. Upstream of spnI there is a gene which we have termed spnT . spnI and spnT form an operon and although database searches failed to reveal any spnT homologues, overexpression of this novel gene negatively affected both sliding motility and prodigiosin production.

Potential Emergence of Multi-quorum Sensing Inhibitor Resistant (MQSIR) Bacteria

“…SpnI/SpnR C6 HSL, C7HSL, C8HSL, 3OC6HSL Sliding motility, biosurfactant production; prodigiosin and nuclease production [170] Serratia plymuthica…”

“…In AI-2 dependent multispecies biofilm communities, suppression of luxS gene expression is expected to lead to variation in interspecies behavior [170][171][172].…”

The Serratia gene cluster encoding biosynthesis of the red antibiotic, prodigiosin, shows species- and strain-dependent genome context variation

“…No evidence of an AHL-dependent quorum-sensing system controlling pigment biosynthesis has been found in any of the other 22 S. marcescens strains tested, of which seven are pigmented (data not shown), implying that quorum-sensing control of prodigiosin production is both highly strain dependent and comparatively rare. Interestingly, a recent report has described a strain of S. marcescens in which pigment is affected by production of OHHL, another AHL (Horng et al, 2002). Where AHLs are made by S. marcescens strains, BHL is usually the molecule produced.…”

Quorum-sensing-directed protein expression in Serratia proteamaculans B5a

“…It has been suggested that EsaR represses the synthesis of extracellular polysaccharide at low cell density, and that the presence of its cognate signal molecule in micromolar amounts results in derepression (Beck von Bodman & Farrand, 1995;Beck von Bodman et al, 1998;Minogue et al, 2002). Other examples of R-proteins that have been proposed to function as repressors include SpnR of Serratia marcescens and YpsP of Yersinia pseudotuberculosis (Atkinson et al, 1999;Horng et al, 2002).The AHL-producing phenotype is widespread among members of the Enterobacteriaceae (e.g. Serratia liquefaciens, Enterobacter agglomerans, Erwinia carotovora, Hafnia alvei and Rahnella aquatilis) Swift et al, 1993Swift et al, , 1999.…”