Attenuation of Virulence in Pathogenic Bacteria Using Synthetic Quorum-Sensing Modulators under Native Conditions on Plant Hosts

Abstract

Quorum sensing (QS) is often critical in both pathogenic and mutualistic relationships between bacteria and their eukaryotic hosts. Gram-negative bacteria typically use N-acylated L-homoserine lactone (AHL) signals for QS. We have identified a number of synthetic AHL analogues that are able to strongly modulate QS in culture-based, reporter gene assays. While informative, these assays represent idealized systems and their relevance to QS under native conditions is often unclear. As one of our goals is to utilize synthetic QS modulators to study bacterial communication under native conditions, identifying robust host-bacteria model systems for their evaluation is crucial. We reasoned that the host-pathogen interaction between Solanum tuberosum (potato) and the Gram-negative pathogen Pectobacterium carotovora would be ideal for such studies as we have identified several potent, synthetic QS modulators for this pathogen, and infection assays in potato are facile. Herein, we report on our development of this host-pathogen system, and another in Phaseolus vulgaris (green bean), as a means for monitoring the ability of abiotic AHLs to modulate QS-regulated virulence in host infection assays. Our assays confirmed that QS modulators previously identified through culture-based assays largely retained their activity profiles when introduced into the plant host. However, inhibition of virulence in wild-type infections was highly dependent on the timing of compound dosing. This study is the first to demonstrate that our AHL analogs are active in wild-type bacteria in their native eukaryotic hosts, and provides compelling evidence for the application of these molecules as probes to study QS in a range of organisms and environments.

Exploiting Quorum Sensing To Confuse Bacterial Pathogens

“…5) (198). Other studies from the Blackwell lab have demonstrated the applicability of various compounds against the pathogenic actions of E. carotovora on Solanum tuberosum (potato) and of P. syringae on Phaseolus vulgaris (green bean), and several compounds showed promising results modulating quorum sensing in both bacteria, though the timing and dosage of treatments, especially in the potato model, were critical (199,201). In another example of cross-inhibition, a high-throughput chemical screen of approximately 35,000 compounds led to the identification of 15 small molecules that inhibited the LuxN/AI-1 QS circuit in V. harveyi (129).…”

Selection of Appropriate Autoinducer Analogues for the Modulation of Quorum Sensing at the Host–Bacterium Interface

“…The utility of synthetic AHL analogues (SAHLAs) as modulators of QS under native conditions (i.e., whilst the bacteria colonizes its natural host) has also been validated in several systems, including: (i) inhibiting virulence factor production by P. carotovorum in infections of Solanum tuberosum (potato) 33 , (ii) enhancing QS-mediated nodulation between strains of Sinorhizobium meliloti and its legume host Medicago truncatula 34 , and (iii) altering V. fischeri bioluminescence in the light organ of Euprymna scolopes , the bobtail squid 36 . The success of these trials is establishing both the concentration and dosing times required for effectively regulating QS signaling in situ .…”

Efficient Biostimulation of Native and Introduced Quorum-Quenching Rhodococcus erythropolis Populations Is Revealed by a Combination of Analytical Chemistry, Microbiology, and Pyrosequencing

“…While B. thuringiensis expresses a unique lactonase, AiiA (13), R. erythropolis expresses three QQ activities, a lactonase (QsdA), an acylase, and a reductase (28,33,34). Aside from the use of biocontrol agents (13,32), QQ molecules (24,27), and QQ transgenic plants (12,16), a biostimulation approach was recently proposed (6,7). It consists of the application of a biodegradable agent, gamma-caprolactone (GCL), to stimulate in the rhizosphere of Solanum tuberosum the growth of endogenous AHL-degrading bacteria (hence the name "biostimulation" to describe this technique).…”