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BMC Systems Biology

, 5:153

Empirical systems biology


BackgroundOne of the puzzles in bacterial quorum sensing is understanding how an organism integrates the information gained from multiple input signals. The marine bacterium Vibrio fischeri regulates its bioluminescence through a quorum sensing mechanism that receives input from three pheromone signals, including two acyl homoserine lactone HSL signals. While the role of the 3-oxo-C6 homoserine lactone 3OC6HSL signal in activating the lux genes has been extensively studied and modeled, the role of the C8 homoserine lactone C8HSL is less obvious, as it can either activate luminescence or block its activation. It remains unclear how crosstalk between C8HSL and 3OC6HSL affects the information that the bacterium obtains through quorum sensing.

ResultsWe have used microfluidic methods to measure the response of individual V.fischeri cells to combinations of C8HSL and 3OC6HSL. By measuring the fluorescence of individual V.fischeri cells containing a chromosomal gfp-reporter for the lux genes, we study how combinations of exogenous HSLs affect both the population average and the cell-to-cell variability of lux activation levels. At the level of a population average, the crosstalk between the C8HSL and 3OC6HSL inputs is well-described by a competitive inhibition model. At the level of individual cells, the heterogeneity in the lux response depends only on the average degree of activation, so that the noise in the output is not reduced by the presence of the second HSL signal. Overall we find that the mutual information between the signal inputs and the lux output is less than one bit. A nonlinear correlation between fluorescence and bioluminescence outputs from lux leads to different noise properties for these reporters.

ConclusionsThe lux genes in V.fischeri do not appear to distinguish between the two HSL inputs, and even with two signal inputs the regulation of lux is extremely noisy. Hence the role of crosstalk from the C8HSL input may not be to improve sensing precision, but rather to suppress the sensitivity of the switch for as long as possible during colony growth.

List of AbbreviationsC8HSLC8 homoserine lactone, N-octanoyl-L-homoserine lactone

GFPgreen fluorescent protein

HSLhomoserine lactone

JB10Vibrio fischeri strain JB10

QSquorum sensing

3OC6HSL3-oxo-C6 homoserine lactone, N-3-oxohexanoyl homoserine lactone.

Electronic supplementary materialThe online version of this article doi:10.1186-1752-0509-5-153 contains supplementary material, which is available to authorized users.

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Autor: Pablo D Pérez - Joel T Weiss - Stephen J Hagen


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