![]() ![]() ![]() To assay indole in culture supernatants, a sample (1 ml) from a growing culture was removed, the OD 600 measured and cells harvested by centrifugation at 11337 x g for 15 seconds (Eppendorf Minispin microfuge). The “raw” assay underpinning the calculation is in the conventional, linear range for the assay. However, these are calculated cell-associated values. The cell associated indole concentrations presented in this report (to a maximum of 60 mM) are much higher than culture medium concentrations measured previously using the Kovacs assay. Kovacs assay is a commonly-used technique in the field which gives consistent results in different laboratories –. We speculate that it may prove to be of widespread significance. This first example of a “pulse signalling” mechanism expands the repertoire of indole effects on bacteria to include ionophore-mediated effects on cell division and growth. In each of these cases the system is responding to relatively low (50 mM) concentration of indole and that this pulse is necessary for long-term stationary phase viability. It can also act as an interkingdom signal and has been shown to affect gene expression in human enterocytes and membrane potential in mitochondria. Indole has diverse signalling roles including modulation of biofilm formation, virulence and stress responses –. In LB medium free tryptophan can range between 0.5–1 mM, and supernatant concentrations of indole also typically reach 0.5–1 mM. The final concentration of indole in stationary phase culture depends upon the amount of tryptophan in the growth medium. However tryptophanase expression is strongly up-regulated by the stationary phase sigma factor RpoS, so indole production rises as cells approach stationary phase. coli makes very little indole during exponential growth. It is produced by the enzyme tryptophanase (TnaA) that converts tryptophan into indole, pyruvate, and ammonia. ![]() Indole is a signalling molecule secreted by over 85 species of bacteria including Escherichia coli. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. JC is also supported by an Internal Graduate Studentship from Trinity College, Cambridge. JC, SHA and UFK acknowledge support from an ERC starting grant,, grant number 261101 Passmembrane. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.įunding: HG was funded by a BBSRC DTG studentship,, grant number PCAG-EJNF. Received: NovemAccepted: FebruPublished: April 2, 2014Ĭopyright: © 2014 Gaimster et al. PLoS ONE 9(4):Įditor: Finbarr Hayes, University of Manchester, United Kingdom The unused resources are used to repair and maintain cells during the extended period of starvation.Ĭitation: Gaimster H, Cama J, Hernández-Ainsa S, Keyser UF, Summers DK (2014) The Indole Pulse: A New Perspective on Indole Signalling in Escherichia coli. We argue that this is sufficient to inhibit growth and division by an ionophore-based mechanism and causes the cells to enter stationary phase before resources are exhausted. During this pulse the cell-associated indole reaches a maximum of approximately 60 mM. We provide evidence that the pertinent signal in this case is not 1 mM indole in the culture supernatant but a transient pulse of intra-cellular indole at the transition from exponential growth to stationary phase. Significantly, the addition of 1 mM indole to the culture supernatant is insufficient to restore long-term survival to the mutant. A mutant that has lost the ability to produce indole demonstrates reduced survival under these conditions. coli cells during long-term stationary phase. Here we describe an alternative mode of indole signalling that promotes the survival of E. Changes are induced by indole concentrations of 0.5–1.0 mM, similar to those found in the supernatant of Escherichia coli stationary phase culture. Indole has diverse signalling roles, including modulation of biofilm formation, virulence and stress responses. ![]()
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