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. 2001 Jul;183(14):4210-6.
doi: 10.1128/JB.183.14.4210-4216.2001.

Indole can act as an extracellular signal in Escherichia coli

D Wang  1 , X Ding, P N Rather
Affiliations

Indole can act as an extracellular signal in Escherichia coli

D Wang et al. J Bacteriol. 2001 Jul.

Abstract

Previous work has shown that lacZ fusions to the cysK, astD, tnaB, and gabT genes in Escherichia coli are activated by self-produced extracellular signals. Using a combination of ethyl acetate extraction, reversed-phase C(18) chromatography, and thin-layer chromatography, we have purified an extracellular activating signal from E. coli supernatants. Mass spectrometry revealed a molecule with an m/z peak of 117, consistent with indole. Nuclear magnetic resonance analysis of the purified E. coli factor and synthetic indole revealed identical profiles. Using synthetic indole, a dose-dependent activation was observed with lacZ fusions to the gabT, astD, and tnaB genes. However, cysK::lacZ and several control fusions were not significantly activated by indole. Conditioned medium prepared from a tnaA (tryptophanase) mutant, deficient in indole production, supported 26 to 41% lower activation of the gabT and astD fusions. The residual level of activation may be due to a second activating signal. Activation of the tnaB::lacZ fusion was reduced by greater than 70% in conditioned medium from a tnaA mutant.

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Figures

FIG. 1
FIG. 1
Electron impact mass spectra of the activating fraction (A) and of synthetic indole (B). The m/z peaks were 117.0584 (C8H7N; calculated, 117.0578) and 90.04767 (C7H6-CHN+).
FIG. 2
FIG. 2
1H NMR spectra of the activating factor and synthetic indole. The chemical shifts are reported in δ (ppm) relative to residual trimethyl silane. The 1H NMR spectra for the activating factor (A) and synthetic indole (B) were identical (see Materials and Methods).
FIG. 3
FIG. 3
Effects of indole on expression. The effects of synthetic indole on expression of lacZ fusions to cysK (MT9), atsD (MT48), tnaB (MT113), and gabT (MT114) were monitored by β-galactosidase expression (Miller units). Average results from duplicate experiments are shown. Standard deviations were less that 10% for each value. Duplicate experiments gave results similar to those shown.
FIG. 4
FIG. 4
Possible model for indole signaling in E. coli. The tnaAB operon is depicted and is activated by CRP-cAMP as nutrients are depleted. This results in indole production via the TnaA (tryptophanase) enzyme. The indole is secreted and acts as an extracellular signal. The components of the signal response pathway are unknown and are indicated by a question mark.
See this image and copyright information in PMC

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