N-Phenylacetanoyl-l-Homoserine Lactones Can Strongly Antagonize or Superagonize Quorum Sensing in Vibrio fischeri

Abstract

Bacteria monitor their population densities using low-molecular-weight ligands in a process known as quorum sensing. At sufficient cell densities, bacteria can change their mode of growth and behave as multicellular communities that play critical roles in both beneficial symbioses and the pathogenesis of infectious disease. The development of non-native ligands that can block quorum-sensing signals has emerged as a promising new strategy to attenuate these divergent outcomes. Here, we report that N-phenylacetanoyl-L-homoserine lactones are capable of either inhibiting or, in some cases, strongly inducing quorum sensing in the bacterial symbiont Vibrio fischeri. Moreover, simple structural modifications to these ligands have remarkable effects on activity. These studies have revealed one of the first synthetic superagonists of quorum sensing, N-(3-nitro-phenylacetanoyl)-L-homoserine lactone. Together, these ligands represent a powerful new class of chemical probes with the potential to significantly expand the current understanding of quorum sensing and its role in host/bacteria interactions.Bacteria can assess their local population densities using low-molecular-weight molecules (auto-inducers) and alter gene expression at high cell number to behave as a group. This process, termed quorum sensing, is widely used by bacteria to initiate group behaviors that have direct and often devastating impacts on human health and the environment (1,2). For example, numerous bacterial pathogens use quorum sensing to initiate infection (3,4). In contrast, symbiotic bacteria use these pathways to commence mutually beneficial relationships with their hosts (2,5,6). Because these important processes are controlled by chemical signals, there is intense and growing interest in the development of non-native ligands that can intercept these signals and attenuate or mimic quorum-sensing outcomes (7).Quorum sensing is best characterized in Gram-negative proteobacteria, which use diffusible N-acylated-L-homoserine lactones (AHLs) and their cognate receptors (R proteins) for intercellular communication (Figure 1, panel a) (2,8). Considerable research efforts have focused on the synthesis of ligands that can disrupt AHL-R protein binding and inhibit quorum sensing (9, 10), yet potent and general R protein antagonists remain scarce. Likewise, compounds exhibiting heightened activities relative to native AHLs (i.e., superagonists of quorum sensing) are also of significant interest, because they could potentially initiate bacterial group behaviors at lower cell numbers than those required in natural environments. For example, superagonists could be used to determine whether beneficial symbioses could be initiated earlier during colonization by a symbiont or whether a pathogen could be forced to *Corresponding author, blackwell@chem.wisc.edu. Note added after print publication: Because of a production error, the DOI was incorrectly listed. This error does not affect the scientific integrity of the article. This paper was originally po...

Comparative Analyses of N‐Acylated Homoserine Lactones Reveal Unique Structural Features that Dictate Their Ability to Activate or Inhibit Quorum Sensing

“…[9][10][11][12][13][14][15][16][17][18][19] Structural modifications to the lactone ring, including inversion of stereochemistry, [20] and replacement of the lactone with different carbo-or heterocycles [9][10][11]17,[21][22][23] have been examined to a lesser degree. Four of the most effective AHL-derived antagonists of TraR, LasR, or LuxR reported to date are shown in Scheme 1: the C 7 AHL 4 active against TraR, [13] the 3-oxo-phenylbutanoyl-and phenylbutanoyl HLs (5 and 6) active against LuxR, [14] and the 2-aminophenol analogue of OdDHL 7 active against LasR.…”

Making Bacteria Behave: New Agonists and Antagonists of Quorum Sensing

“…Their use of a luxR Ϫ control strain establishes that the most active agonists require the LuxR protein for their activity, an indication of its specificity for interaction of the analogue with LuxR and not at any other point in the quorum-sensing pathway. Geske et al (4) are able to draw some conclusions about structure-activity relationships with the set of molecules and the "remarkable and varied" activities that they present in this paper. Interestingly, the original N-(4-bromophenylacetyl-)-L-homoserine lactone (1a) structure upon which all of the AHL analogues in this paper are designed was initially identified as an antagonist of quorum-sensing activity in A. tumefaciens and P. aeruginosa, and it is now being shown to be a strong inhibitor of V. fischeri as well (4).…”

“…Geske et al (4) are able to draw some conclusions about structure-activity relationships with the set of molecules and the "remarkable and varied" activities that they present in this paper. Interestingly, the original N-(4-bromophenylacetyl-)-L-homoserine lactone (1a) structure upon which all of the AHL analogues in this paper are designed was initially identified as an antagonist of quorum-sensing activity in A. tumefaciens and P. aeruginosa, and it is now being shown to be a strong inhibitor of V. fischeri as well (4). This is surprising, because the well-established specificity of bacteria toward their own AHL suggests that each individual R protein has evolved exquisite specificity toward its own native ligand.…”

“…The strong and opposing activity of 1b containing the same basic framework as 1a but differing in the substitution on the aryl group emphasizes that only a very uncertain line can be drawn to differentiate agonist from antagonist structures. Geske et al (4) report that preliminary in silico docking studies suggest that the 3-substituted aryl analogues are accommodated better than the 4-substituted analogues in the binding site of TraR; full understanding will require more analysis of this sort.…”

A structural perspective on the mechanisms of quorum sensing activation in bacteria

“…Several clinically-relevant bacteria regulate virulence factor production by QS systems, and multidrug resistance is characteristic of these infections (Hentzer et al 2003, Clatworthy et al 2007, Geske et al 2007, Kievit and Iglewski 2000. Thus, the development of antimicrobials that target QS pathways represents an important therapeutic strategy, since QS disturbance attenuates the bacteria pathogenicity without being lethal (Wu et al 2004, Rasmussen andGivskov 2006a).…”