Quorum sensing activity of Mesorhizobium sp. F7 isolated from potable water.

Pei-Ling Yong,Kok-Gan Chan

doi:10.1155/2014/874764

Abstract

We isolated a bacterial isolate (F7) from potable water. The strain was identified as Mesorhizobium sp. by 16S rDNA gene phylogenetic analysis and screened for N-acyl homoserine lactone (AHL) production by an AHL biosensor. The AHL profile of the isolate was further analyzed using high resolution triple quadrupole liquid chromatography mass spectrometry (LC/MS) which confirmed the production of multiple AHLs, namely, N-3-oxo-octanoyl-L-homoserine lactone (3-oxo-C8-HSL) and N-3-oxo-decanoyl-L-homoserine lactone (3-oxo-C10-HSL). These findings will open the perspective to study the function of these AHLs in plant-microbe interactions.

Highlights

Bacterial cell-cell communication, termed quorum sensing (QS), occurs when the cell density has reached a threshold level that could regulate gene expressions via signalling molecules [1, 2]
Acyl-homoserine lactones (AHLs) molecules which are responsible for QS activity are synthesized by acyl homoserine lactone (AHL) synthase (LuxI homologue) whereby AHL will bind to its cognate receptor (LuxR homologue) to form a AHL-LuxR complex which in turn modulates a battery of QSmediated gene expression [3, 4]
The various functions regulated by AHLs of Rhizobium and Sinorhizobium range from exopolysaccharide production [13], rhizosphere-related gene expression [14], and the conjugal transfer of pSym plasmids [15]

Summary

Introduction

Bacterial cell-cell communication, termed quorum sensing (QS), occurs when the cell density has reached a threshold level that could regulate gene expressions via signalling molecules [1, 2]. Rhizobia which include the genera Rhizobium, Sinorhizobium, Mesorhizobium, Azorhizobium, and Bradyrhizobium exhibit nitrogen fixing properties in root nodules of legumes which can only be achieved when bacteria carry large selftransmissible genetic elements, either plasmids or integrating conjugative elements that include symbiotic genes [9]. The various functions regulated by AHLs of Rhizobium and Sinorhizobium range from exopolysaccharide production [13], rhizosphere-related gene expression [14], and the conjugal transfer of pSym plasmids [15]. Strain NGR234, it was found that the production of 3-oxo-C8-HSL led to activation of the transcriptional regulator TraR which significantly decreased the growth rate of NGR234 [15]. It was shown that the regulatory gene TraI of Rhizobium etli CFN42 controls synthesis of 3-oxo-C8-HSL and conjugative plasmid transfer [17]. F7 which was isolated from potable water We showed that this strain produces two AHLs, 3-oxo-C8-HSL and 3-oxoC10-HSL

Experimental Section

Results and Discussion

Conflict of Interests