Quorum sensing in Escherichia coli, Salmonella typhimurium, and Vibrio harveyi: a new family of genes responsible for autoinducer production - PubMed (original) (raw)

Quorum sensing in Escherichia coli, Salmonella typhimurium, and Vibrio harveyi: a new family of genes responsible for autoinducer production

M G Surette et al. Proc Natl Acad Sci U S A. 1999.

Abstract

In bacteria, the regulation of gene expression in response to changes in cell density is called quorum sensing. Quorum-sensing bacteria produce, release, and respond to hormone-like molecules (autoinducers) that accumulate in the external environment as the cell population grows. In the marine bacterium Vibrio harveyi two parallel quorum-sensing systems exist, and each is composed of a sensor-autoinducer pair. V. harveyi reporter strains capable of detecting only autoinducer 1 (AI-1) or autoinducer 2 (AI-2) have been constructed and used to show that many species of bacteria, including Escherichia coli MG1655, E. coli O157:H7, Salmonella typhimurium 14028, and S. typhimurium LT2 produce autoinducers similar or identical to the V. harveyi system 2 autoinducer AI-2. However, the domesticated laboratory strain E. coli DH5alpha does not produce this signal molecule. Here we report the identification and analysis of the gene responsible for AI-2 production in V. harveyi, S. typhimurium, and E. coli. The genes, which we have named luxSV.h., luxSS.t., and luxSE.c. respectively, are highly homologous to one another but not to any other identified gene. E. coli DH5alpha can be complemented to AI-2 production by the introduction of the luxS gene from V. harveyi or E. coli O157:H7. Analysis of the E. coli DH5alpha luxSE.c. gene shows that it contains a frameshift mutation resulting in premature truncation of the LuxSE.c. protein. Our results indicate that the luxS genes define a new family of autoinducer-production genes.

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Figures

Figure 1

Figure 1

The luxS and ygaG genes from V. harveyi and E. coli MG1655. (A) A restriction map of the V. harveyi luxS V.h. chromosomal region that was defined by Tn_5_ insertion. The sites of Tn_5_ insertions that disrupted the AI-2-production function and one control Tn_5_ insertion outside of the_luxS_V.h. locus are shown (triangles). (B) The ygaG region in the E. coli MG1655 chromosome. This ORF is flanked by the_emrB_ and gshA genes. The direction of transcription of each gene is indicated by horizontal arrows. The corresponding position of the MudJ insertion that eliminated AI-2 production in S. typhimurium LT2 is shown by a vertical arrow. H, R, P, and B denote _Hin_dIII,_Eco_RI, _Pst_I, and _Bam_HI restriction sites, respectively.

Figure 2

Figure 2

Autoinducer-production phenotypes of V. harveyi and S. typhimurium strains. Cell-free culture fluids from V. harveyi and S. typhimurium strains were prepared and tested for AI-2 activity in the V. harveyi BB170 bioassay. (A) AI-2 production phenotypes of the wild-type V. harveyi strain MM28, which contains a Tn_5_ insertion outside of_luxS_ V.h. (denoted WT) and the_luxS_ _V.h.∷Tn_5 mutant strain MM30 (denoted _luxS_−). (B) AI-2-production phenotypes of wild-type S. typhimurium LT2 (denoted WT) and the _ygaG_∷MudJ insertion mutant strain CS132 (denoted _ygaG_−). Activity is reported as fold-induction of luminescence expression of the V. harveyi BB170 reporter strain over that when sterile medium was added.

Figure 3

Figure 3

Complementation of AI-2 production in S. typhimurium CS132 and E. coli DH5α. Cell-free culture fluids from E. coli and S. typhimurium strains were tested for AI-2 activity in the bioassay. The activity present in these fluids was compared with that produced by wild-type V. harveyi BB120. The level of BB120 activity was normalized to 100%. (A) AI-2 activity in cell-free fluids from wild-type V. harveyi BB120,E. coli O157:H7, and S. typhimurium LT2. (B) Complementation of S. typhimurium CS132 (ygaG_∷MudJ). (C) Complementation of_E. coli DH5α. In B and_C_, the in trans AI-2 production genes are the following: vector control (“none”), E. coli O157:H7 ygaG, and V. harveyi BB120_luxS_ V.h.. E.c., E. coli; V.h., V. harveyi.

Figure 4

Figure 4

Alignment of LuxS and YgaG protein sequences. The translated protein sequences for the AI-2 production family of proteins are shown. We determined the sequences for the_luxS_ V.h. gene from V. harveyi BB120 and the ygaG genes from E. coli MG1655, E. coli O157:H7, and E. coli DH5α. The S. typhimurium LT2_ygaG_ partial sequence came from the S. typhimurium database. Amino acid residues that are not identical to the LuxS_V.h._ protein are underlined. The site of the frameshift mutation in the E. coli DH5α DNA sequence is denoted by ∗. The 20 altered amino acid residues that are translated after the frameshift are enclosed by the box.

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