The biocontrol strain Pseudomonas fluorescens F113 produces the Rhizobium small bacteriocin, N-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone, via HdtS, a putative novel N-acylhomoserine lactone synthase The GenBank accession number for the sequence determined in this work is AF286536.

Abstract

Several different species of Pseudomonas produce N-acylhomoserine lactones (AHLs), quorum-sensing signal molecules which are involved in the cell-densitydependent control of secondary metabolite and virulence gene expression. When Pseudomonas fluorescens F113 was cross-streaked against AHL biosensors capable of sensitively detecting either short (C 4 -C 8 ) or long (C 10 -C 14 ) acyl chain AHLs, no activity was detectable. However, by extracting cell-free stationary-phase culture supernatants with dichloromethane followed by reverse-phase HPLC, three distinct fractions were obtained capable of activating the AHL biosensors. Three AHLs were subsequently characterized using high-resolution MS and chemical synthesis. These were (i) N-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone (3OH,C 14 :1 -HSL), a molecule previously known as the Rhizobium leguminosarum small bacteriocin as a consequence of its growth inhibitory properties, (ii) N-decanoylhomoserine lactone (C 10 -HSL) and (iii) N-hexanoylhomoserine lactone (C 6 -HSL). A gene (hdtS) capable of directing synthesis of all three P. fluorescens AHLs in Escherichia coli was cloned and sequenced. In vitro transcription/translation of hdtS yielded a protein of approximately 33 kDa capable of directing the synthesis of 3OH,C 14 :1 -HSL, C 10 -HSL and C 6 -HSL in E. coli. HdtS does not belong to either of the known AHL synthase families (LuxI or LuxM) and is related to the lysophosphatidic acid acyltransferase family. HdtS may therefore constitute a member of a third protein family capable of AHL biosynthesis.

Cell Density-Dependent Gene Contributes to Efficient Seed Colonization by Pseudomonas putida KT2440

“…As a preliminary characterization of the nature of the signaling molecule(s) involved, culture supernatant of KT2440 was subjected to different treatments prior to its addition to KT2440(pME510) cells. An increase in ␤-galactosidase activity similar to that observed with the untreated supernatant was observed after 15 min at 100°C or treatment with 10 g of proteinase K/ml for 1 h. Although bioassays with reporter strains that respond to different AHLs produced negative results (data not shown), it seemed possible that KT2440 produced an AHL molecule that was not recognized by these reporters, a phenomenon that is not uncommon (27). Since AHL-type molecules suffer hydrolization of the lactone ring at high pH and are stable at low pH, we decided to test the effects of raising or lowering the pH of conditioned medium (to 9.5 or 4.5, respectively).…”

“…We have done a search in the genome sequence of KT2440 that has revealed the absence of genetic loci homologous to those involved in the synthesis of quorum-sensing signals in other organisms. The only exception is a gene similar to hdtS, which in P. fluorescens F113 has been proposed to participate in the synthesis of certain AHLs (27). The role of this gene in P. putida KT2440, and its potential involvement in signal synthesis and/or ddcA expression, remains to be elucidated.…”

Comparison of the complete genome sequences of Pseudomonas syringae pv. syringae B728a and pv. tomato DC3000

“…N-AHL synthase AhlI and the regulator AhlR were identified in Pss B728a (22) (AhlI-AhlR, Psyr1621-1622), and the single predominant AHL produced by this strain has been shown to comigrate on a chromatogram with a N-3-oxo-hexanoyl-L-homoserine lactone standard (23). Another potential AHL synthase similar to acyltransferases of the PlsC family is encoded by Psyr0009, which has 82% sequence identity with the HdtS protein of P. fluorescens F113 (24). HdtS is capable of producing three AHLs, including N-(3-hydroxy-7-cis-tetradecenoyl) homoserine lactone, a molecule also known as the Rhizobium leguminosarum small bacteriocin as a consequence of its growth-inhibiting properties.…”

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

“…In Pseudomonas chlororaphis and P. fluorescens, multiple QSS (PhzI/R; CsaI/R, MpuI/R, and HdytS) regulate the biosynthesis of phenazine and pyrrolnitrin, and play an active role in rhizosphere colonization through signal molecules ranging from C4HSL to C10HSL, and others like hydroxy-and oxo-substitutions, and DKPs ( Table 2) [70][71][72][73].…”