N-hexanoyl-l-homoserine lactone, a mediator of bacterial quorum-sensing regulation, exhibits plant-dependent stability and may be inactivated by germinating Lotus corniculatus seedlings

Abstract

The half-life of N-hexanoyl-l-homoserine lactone (C6-HSL) was determined under various pH and temperature conditions, and in several plant environments. C6-HSL was sensitive to alkaline pH, a process that was also temperature-dependent. In addition, C6-HSL disappeared from plant environments, i.e. axenic monocot and dicot plants cultivated under gnotobiotic, hydroponic conditions, albeit with variable kinetics. The disappearance was rapid at the root system of legume plants such as clover or Lotus, and slow or non-existent at the root system of monocots such as wheat or corn. These variable kinetics were not dependent upon pH changes that may have affected the growth media of the plants. Furthermore, C6-HSL did not accumulate in the plant, and the plant did not produce inhibitors of the C6-HSL signal. HPLC analyses revealed that C6-HSL disappeared from the media, and hence, Lotus exhibited a natural C6-HSL inactivating ability. This ability was not specific for C6-HSL and allowed the degradation of other N-acyl-homoserine lactones such as 3-oxo-C6-HSL, 3-oxo-octanoyl-HSL and 3-oxo-decanoyl-HSL. Preliminary investigation revealed that the inactivating ability is temperature-dependant and possibly of enzymatic origin.

Microbial interactions associated with biofilms attached to Trichodesmium spp. and detrital particles in the ocean

“…The effect of pH on the abiotic degradation of AHLs in aqueous media (LB media, organic buffers or pure water) is well established: AHLs degrade more rapidly at higher pH , Delalande et al 2005. In seawater, with an average pH of 8.2, AHLs are expected to degrade quite rapidly.…”

“…It has been shown that AHLs are very short-lived in aqueous media with pH in the range of seawater . Furthermore, it appears that AHLs are also degraded enzymatically in natural systems (Delalande et al 2005, Wang & Leadbetter 2005, a process that has been termed "quorum quenching".…”

“…Multiple AHLs may be used by the same organism to regulate independent processes (Gonzalez & Marketon 2003 and refs therein). Importantly, the rate of both abiotic degradation and quorum quenching also appears to be affected by these aforementioned variations in AHL structure , Delalande et al 2005, Wang & Leadbetter 2005. It is likely, although not demonstrated, that organisms will produce a particular suite of AHLs based on each molecule's stability in a given environment.…”

Quorum sensing, communication and cross-kingdom signalling in the bacterial world

“…In airway epithelia, PON2 appears to be the most efficient degrader of 3-oxo-C12-HSL and consequently is considered likely to contribute to host defences against bacteria such as P. aeruginosa (Stoltz et al, 2007). Germinating seedlings of the leguminous plant Lotus corniculatus have also been shown to be capable of enzymically inactivating a wide range of AHLs, although the mechanism involved has yet to be established (Delalande et al, 2005).…”

l-Canavanine Made byMedicago sativaInterferes with Quorum Sensing inSinorhizobium meliloti

“…Teplitski et al have shown that various species of higher plants, including pea seedlings, secrete a series of unidentified signals that are capable of interfering with the quorum-sensing behavior of several bacterial reporter strains (49). This would suggest that plants may have evolved mechanisms to interfere with or respond to bacterial quorum sensing and thereby have the potential to manipulate the behavior of the associated bacteria to their advantage (8,20,34,49).…”