scholarly journals Induction and Loss of Ti Plasmid Conjugative Competence in Response to the Acyl-Homoserine Lactone Quorum-Sensing Signal

2008 ◽  
Vol 190 (13) ◽  
pp. 4398-4407 ◽  
Author(s):  
Shengchang Su ◽  
Sharik R. Khan ◽  
Stephen K. Farrand
Keyword(s):  
Quorum Sensing ◽  
Homoserine Lactone ◽  
Maximum Activity ◽  
Ti Plasmid ◽  
Conjugative Transfer ◽  
Acyl Homoserine Lactone ◽  
Sensing System ◽  
Ti Plasmids ◽  
Crown Gall Tumors ◽  
Kinetics Of

ABSTRACT Conjugative transfer of the Ti plasmids of Agrobacterium tumefaciens is controlled by a quorum-sensing system composed of TraR and its signal N-(3-oxo-octanoyl)-l-homoserine lactone. This system is, in turn, controlled by the conjugative opines produced by crown gall tumors induced on plants by the bacteria. Using nonpolar traI mutants, we examined the kinetics of induction of conjugative transfer in response to exogenous acyl-homoserine lactone. In the absence of the antiactivator TraM, onset of induction of transfer requires about 30 min, 15 to 20 min of which is needed for expression and construction of the conjugative apparatus. TraM delays the onset of conjugation by 30 min. While the rate of development of conjugative competence was not significantly affected by levels of TraR, maximum efficiencies of transfer were correlated with amounts of the activator in the donors. Donors harboring Ti plasmids lacking TraM were fully induced by the quormone at concentrations as low as 100 pM. TraM raised the concentration of signal required for maximum activity to 1 nM. Donors grown in batch culture retained conjugative competence following signal removal, even when in stationary phase. However, donors kept in balanced growth rapidly lost transfer ability following signal removal. Loss of transfer was mirrored by a decrease in levels of active TraR. Decreases in TraR activity and conjugative competence could be accounted for by dilution associated with cell division, suggesting that while induction of Ti plasmid conjugation is an active process, the cells lack a mechanism for disassembling the conjugative apparatus when signals become limiting.

scholarly journals The BlcC (AttM) Lactonase of Agrobacterium tumefaciens Does Not Quench the Quorum-Sensing System That Regulates Ti Plasmid Conjugative Transfer

2008 ◽  
Vol 191 (4) ◽  
pp. 1320-1329 ◽  
Author(s):  
Sharik R. Khan ◽  
Stephen K. Farrand
Keyword(s):  
Agrobacterium Tumefaciens ◽  
Quorum Sensing ◽  
Homoserine Lactone ◽  
Ti Plasmid ◽  
Mutation Induction ◽  
Conjugative Transfer ◽  
Wild Type ◽  
In Planta ◽  
Sensing System ◽  
Quorum Sensing System

ABSTRACT The conjugative transfer of Agrobacterium plasmids is controlled by a quorum-sensing system consisting of TraR and its acyl-homoserine lactone (HSL) ligand. The acyl-HSL is essential for the TraR-mediated activation of the Ti plasmid Tra genes. Strains A6 and C58 of Agrobacterium tumefaciens produce a lactonase, BlcC (AttM), that can degrade the quormone, leading some to conclude that the enzyme quenches the quorum-sensing system. We tested this hypothesis by examining the effects of the mutation, induction, or mutational derepression of blcC on the accumulation of acyl-HSL and on the conjugative competence of strain C58. The induction of blc resulted in an 8- to 10-fold decrease in levels of extracellular acyl-HSL but in only a twofold decrease in intracellular quormone levels, a measure of the amount of active intracellular TraR. The induction or mutational derepression of blc as well as a null mutation in blcC had no significant effect on the induction of or continued transfer of pTiC58 from donors in any stage of growth, including stationary phase. In matings performed in developing tumors, wild-type C58 transferred the Ti plasmid to recipients, yielding transconjugants by 14 to 21 days following infection. blcC-null donors yielded transconjugants 1 week earlier, but by the following week, transconjugants were recovered at numbers indistinguishable from those of the wild type. Donors mutationally derepressed for blcC yielded transconjugants in planta at numbers 10-fold lower than those for the wild type at weeks 2 and 3, but by week 4, the two donors showed no difference in recoverable transconjugants. We conclude that BlcC has no biologically significant effect on Ti plasmid transfer or its regulatory system.

scholarly journals Co-Dependent and Interdigitated: Dual Quorum Sensing Systems Regulate Conjugative Transfer of the Ti Plasmid and the At Megaplasmid in Agrobacterium tumefaciens 15955

2020 ◽  
Author(s):  
Ian S Barton ◽  
Justin L Eagan ◽  
Priscila A Nieves-Otero ◽  
Ian P Reynolds ◽  
Thomas G Patt ◽  
...  
Keyword(s):  
Agrobacterium Tumefaciens ◽  
Quorum Sensing ◽  
Homoserine Lactone ◽  
Ti Plasmid ◽  
Conjugative Transfer ◽  
Gene Promoters ◽  
Transcription Activator ◽  
Conjugation System ◽  
Direct Production ◽  
Sensing Systems

Members of the Rhizobiaceae, often carry multiple secondary replicons in addition to the primary chromosome with compatible repABC-based replication systems. Unlike secondary chromosomes and chromids, repABC-based megaplasmids and plasmids can undergo copy number fluctuations and are capable of conjugative transfer in response to environmental signals. Several Agrobacterium tumefaciens lineages harbor three secondary repABC-based replicons, including a secondary chromosome (often linear), the Ti (tumor-inducing) plasmid and the At megaplasmid. The Ti plasmid is required for virulence and encodes a conjugative transfer (tra) system that is strictly regulated by a subset of plant-tumor released opines and a well-described acyl-homoserine lactone (AHL)-based quorum-sensing mechanism. At plasmids are generally not required for virulence, but carry genes that enhance rhizosphere survival, and these plasmids are often conjugatively proficient. We report that the At megaplasmid of the octopine-type strain A. tumefaciens 15955 encodes a quorum-controlled conjugation system that directly interacts with the paralogous quorum sensing system on the co-resident Ti plasmid. Both the pAt15955 and pTi15955 plasmids carry homologues of a TraI-type AHL synthase, a TraR-type AHL-responsive transcription activator, and a TraM-type anti-activator. The traI genes from both pTi15955 and pAt15955 can direct production of the inducing AHL (3-octanoyl-L-homoserine lactone) and together contribute to the overall AHL pool. The TraR protein encoded on each plasmid activates AHL-responsive transcription of target tra gene promoters. The pAt15955 TraR can cross-activate tra genes on the Ti plasmid as strongly as its cognate tra genes, whereas the pTi15955 TraR preferentially biased towards its own tra genes. Putative tra box elements are located upstream of target promoters, and comparing between plasmids, they are in similar locations and share an inverted repeat structure, but have distinct consensus sequences. The two AHL quorum sensing systems have a combinatorial effect on conjugative transfer of both plasmids. Overall, the interactions described here have implications for the horizontal transfer and evolutionary stability of both plasmids and, in a broad sense, are consistent with other repABC systems that often have multiple quorum-sensing controlled secondary replicons.

scholarly journals Two Opines Control Conjugal Transfer of an Agrobacterium Plasmid by Regulating Expression of Separate Copies of the Quorum-Sensing Activator Gene traR

2002 ◽  
Vol 184 (4) ◽  
pp. 1121-1131 ◽  
Author(s):  
Philippe Oger ◽  
Stephen K. Farrand
Keyword(s):  
Quorum Sensing ◽  
Regulatory System ◽  
Homoserine Lactone ◽  
Conjugal Transfer ◽  
Environmental Cues ◽  
Upstream Gene ◽  
Catabolic Plasmid ◽  
Ti Plasmids ◽  
Control Transfer ◽  
Crown Gall Tumors

ABSTRACT Conjugal transfer of Ti plasmids from Agrobacterium spp. is controlled by a hierarchical regulatory system designed to sense two environmental cues. One signal, a subset of the opines produced by crown gall tumors initiated on plants by the pathogen, serves to induce production of the second, an acyl-homoserine lactone quorum-sensing signal, the quormone, produced by the bacterium itself. This second signal activates TraR, and this transcriptional activator induces expression of the tra regulon. Opines control transfer because the traR gene is a member of an operon the expression of which is regulated by the conjugal opine. Among the Ti plasmid systems studied to date, only one of the two or more opine families produced by the associated tumor induces transfer. However, two chemically dissimilar opines, nopaline and agrocinopines A and B, induce transfer of the opine catabolic plasmid pAtK84b found in the nonpathogenic Agrobacterium radiobacter isolate K84. In this study we showed that this plasmid contains two copies of traR, and each is associated with a different opine-regulated operon. One copy, traR noc, is the last gene of the nox operon and was induced by nopaline but not by agrocinopines A and B. Mutating traR noc abolished induction of transfer by nopaline but not by the agrocinopines. A mutation in ocd, an upstream gene of the nox operon, abolished utilization of nopaline and also induction of transfer by this opine. The second copy, traR acc, is located in an operon of four genes and was induced by agrocinopines A and B but not by nopaline. Genetic analysis indicated that this gene is required for induction of transfer by agrocinopines A and B but not by nopaline. pAtK84b with mutations in both traR genes was not induced for transfer by either opine. However, expression of a traR gene in trans to this plasmid resulted in opine-independent transfer. The association of traR noc with nox is unique, but the operon containing traR acc is related to the arc operons of pTiC58 and pTiChry5, two Ti plasmids inducible for transfer by agrocinopines A-B and C-D, respectively. We conclude that pAtK84b codes for two independently functioning copies of traR, each regulated by a different opine, thus accounting for the activation of the transfer system of this plasmid by the two opine types.

scholarly journals Quorum Sensing but Not Autoinduction of Ti Plasmid Conjugal Transfer Requires Control by the Opine Regulon and the Antiactivator TraM

2000 ◽  
Vol 182 (4) ◽  
pp. 1080-1088 ◽  
Author(s):  
Kevin R. Piper ◽  
Stephen K. Farrand
Keyword(s):  
Quorum Sensing ◽  
Control Process ◽  
Population Level ◽  
Homoserine Lactone ◽  
Ti Plasmid ◽  
Conjugal Transfer ◽  
Population Densities ◽  
Independent Manner ◽  
Ti Plasmids ◽  
Donor Population

ABSTRACT Conjugal transfer of the Ti plasmids from Agrobacterium tumefaciens is controlled by autoinduction via the transcriptional activator TraR and the acyl-homoserine lactone ligand,Agrobacterium autoinducer (AAI). This control process is itself regulated by opines, which are small carbon compounds produced by the crown gall tumors that are induced by the bacteria. Opines control autoinduction by regulating the expression of traR. Transfer of pTiC58 from donors grown with agrocinopines A and B, the conjugal opines for this Ti plasmid, was detected only after the donors had reached a population level of 107 cells per cm2. Donors incubated with the opines and AAI transferred their Ti plasmids at population levels about 10-fold lower than those incubated with opines only. Transcription of the traregulon, as assessed by monitoring atraA::lacZ reporter, showed a similar dependence on the density of the donor population. However, even in cultures at low population densities that were induced with opines and AAI, there was a temporal lag of between 15 and 20 h in the development of conjugal competence. Moreover, even after this latent period, maximal transfer frequencies required several hours to develop. This lag period was independent of the population density of the donors but could be reduced somewhat by addition of exogenous AAI. Quorum-dependent development of conjugal competence required control by the opine regulon; donors harboring a mutant of pTiC58 deleted for the master opine responsive repressor accR transferred the Ti plasmid at maximum frequencies at very low population densities. Similarly, an otherwise wild-type derivative of pTiC58 lackingtraM, which codes for an antiactivator that inhibits TraR activity, transferred at high frequency in a population-independent manner in the absence of the conjugal opines. Thus, while quorum sensing is dependent upon autoinduction, the two phenomena are not synonymous. We conclude that conjugal transfer of pTiC58 is regulated in a quorum-dependent fashion but that supercontrol of the TraR-AAI system by opines and by TraM results in a complex control process that requires not only the accumulation of AAI but also the expression of TraR and the synthesis of this protein at levels that overcome the inhibitory activity of TraM.

scholarly journals The Burkholderia mallei BmaR3-BmaI3 Quorum-Sensing System Produces and Responds to N-3-Hydroxy-Octanoyl Homoserine Lactone

2008 ◽  
Vol 190 (14) ◽  
pp. 5137-5141 ◽  
Author(s):  
Breck A. Duerkop ◽  
Jake P. Herman ◽  
Ricky L. Ulrich ◽  
Mair E. A. Churchill ◽  
E. Peter Greenberg
Keyword(s):  
Escherichia Coli ◽  
Quorum Sensing ◽  
Homoserine Lactone ◽  
Acyl Homoserine Lactone ◽  
Burkholderia Mallei ◽  
E Coli ◽  
Additional Signal ◽  
Sensing System ◽  
Quorum Sensing System ◽  
Signal Receptors

ABSTRACT Burkholderia mallei has two acyl-homoserine lactone (acyl-HSL) signal generator-receptor pairs and two additional signal receptors, all of which contribute to virulence. We show that B. mallei produces N-3-hydroxy-octanoyl HSL (3OHC8-HSL) but a bmaI3 mutant does not. Recombinant Escherichia coli expressing BmaI3 produces hydroxylated acyl-HSLs, with 3OHC8-HSL being the most abundant compound. In recombinant E. coli, BmaR3 responds to 3OHC8-HSL but not to other acyl-HSLs. These data indicate that the signal for BmaR3-BmaI3 quorum sensing is 3OHC8-HSL.

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