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Detection of other microbial species by Salmonella: expression of the SdiA regulon.

ABSTRACT: Salmonella, Escherichia, and Klebsiella do not encode any recognized type of N-acylhomoserine lactone (AHL) synthase, and consistent with this, they do not synthesize AHLs under any conditions tested. However, they do encode an AHL receptor of the LuxR family, named SdiA. MudJ fusions in four loci are known to respond to plasmid-encoded sdiA in Salmonella, but only the rck locus has been described. Here we report the location and sequence analysis of the remaining three loci. The srg-6::MudJ is within gtgA of the gifsy-2 prophage, and the srg-7::MudJ is within PSLT61 of the virulence plasmid. Both fusions are in the antisense orientation. The third fusion, srgE5::MudJ, is within a horizontally acquired gene of unknown function at 33.6 centisomes that we have named srgE. Previously, sdiA expressed from its natural position in the chromosome was demonstrated to activate a plasmid-based transcriptional fusion to the rck promoter in response to AHL production by other bacterial species. However, the MudJ fusions did not respond to chromosomal sdiA. Here we report that MudJ fusions to three of the four loci (not srg-6) are activated by AHL in an sdiA-dependent manner during growth in motility agar (0.25% agar) but not during growth in top agar (0.7% agar) or on agar plates (1.2% agar). In motility agar, the srgE promoter responds to sdiA at 30 degrees C and higher while the rck and srg-7 promoters respond only at 37 or 42 degrees C. Substantial AHL-independent SdiA activity was observed at 30 degrees C but not at 37 degrees C.

SUBMITTER: Smith JN

PROVIDER: S-EPMC142872 | biostudies-literature | 2003 Feb

REPOSITORIES: biostudies-literature

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Detection of other microbial species by Salmonella: expression of the SdiA regulon.

Smith Jenée N JN Ahmer Brian M M BM

Journal of bacteriology 20030201 4

Salmonella, Escherichia, and Klebsiella do not encode any recognized type of N-acylhomoserine lactone (AHL) synthase, and consistent with this, they do not synthesize AHLs under any conditions tested. However, they do encode an AHL receptor of the LuxR family, named SdiA. MudJ fusions in four loci are known to respond to plasmid-encoded sdiA in Salmonella, but only the rck locus has been described. Here we report the location and sequence analysis of the remaining three loci. The srg-6::MudJ is ...[more]

PMID: 12562806

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Project description:As a stationary phase signal, indole is secreted in large quantities into rich medium by Escherichia coli and has been shown to control several genes (e.g., astD, tnaB, gabT), multi-drug exporters, and the pathogenicity island of E. coli; however, its impact on biofilm formation has not been well-studied.Through a series of global transcriptome analyses, confocal microscopy, isogenic mutants, and dual-species biofilms, we show here that indole is a non-toxic signal that controls E. coli biofilms by repressing motility, inducing the sensor of the quorum sensing signal autoinducer-1 (SdiA), and influencing acid resistance (e.g., hdeABD, gadABCEX). Isogenic mutants showed these associated proteins are directly related to biofilm formation (e.g., the sdiA mutation increased biofilm formation 50-fold), and SdiA-mediated transcription was shown to be influenced by indole. The reduction in motility due to indole addition results in the biofilm architecture changing from scattered towers to flat colonies. Additionally, there are 12-fold more E. coli cells in dual-species biofilms grown in the presence of Pseudomonas cells engineered to express toluene o-monooxygenase (TOM, which converts indole to an insoluble indigoid) than in biofilms with pseudomonads that do not express TOM due to a 22-fold reduction in extracellular indole. Also, indole stimulates biofilm formation in pseudomonads. Further evidence that the indole effects are mediated by SdiA and homoserine lactone quorum sensing is that the addition of N-butyryl-, N-hexanoyl-, and N-octanoyl-L-homoserine lactones repress E. coli biofilm formation in the wild-type strain but not with the sdiA mutant.Indole is an interspecies signal that decreases E. coli biofilms through SdiA and increases those of pseudomonads. Indole may be manipulated to control biofilm formation by oxygenases of bacteria that do not synthesize it in a dual-species biofilm. Furthermore, E. coli changes its biofilm in response to signals it cannot synthesize (homoserine lactones), and pseudomonads respond to signals they do not synthesize (indole).

Dataset Information

Detection of other microbial species by Salmonella: expression of the SdiA regulon.

Publications

Detection of other microbial species by Salmonella: expression of the SdiA regulon.

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