Quorum Sensing in Bacteria: How a Picture can be Worth a Thousand Words

Increasingly, multimedia and video are being used in addition to traditional delivery methods to communicate scientific findings. Journals such as PLoS ONE, Cell, Nature and others often use video to either showcase particular articles, or offer authors the opportunity to include multimedia elements as part of their article. Some subjects lend themselves better to video delivery than others. Every so often a video report comes along that perfectly complements the content of the associated paper, illustrating the power of video to enhance communication of research findings.

In my opinion, the effective use of video to highlight results is beautifully illustrated by the report below, highlighting the publication “A synchronized quorum of genetic clocks” by Danino et al, which was published in Nature this week.

[youtube=http://www.youtube.com/watch?v=pnjdAr4EjI0]

Quorum sensing is used to coordinate gene expression by several bacterial species. The classic example being that of Vibrio fischeri, a symbiont that lives in the light-producing organ of the Hawaiian bobtailed squid. Free-living bacteria do not glow because the concentration of the luminescence inducer is too low. However, as bacterial concentration increases (in the light-producing organ of the squid), the concentration of the inducer increases sufficiently for luminescence to occur. Therefore, the expression of the luminescence genes is controlled by the local density of the bacterial population.

The Nature paper describes quorum sensing in an artificial system created using E. coli genetically engineered to contain the luxI gene from V. fischeri, the aiiA gene from Bacillus thuringiensis and a GFP fusion protein, all under the control of copies of the luxI promoter. LuxI activation leads to the production of a small molecule (AHL) that crosses the cell membrane and is the mediator of intracellular communication. It enters other cells and triggers a process that activates the luxI promoter, resulting (in this system) in the transcription of GFP and the associated fluorescence. AiiA negatively regulates the promoter by catalyzing the degradation of AHL.

Under normal circumstances, pulsed fluorescence would not occur, as the accumulated AHL within the colony would ultimately cause quenching. To generate the continuous and coordinated pulses observed in the video, the authors used a microfluidic device with a chamber containing a high concentration of bacterial cells that also allowed a continuous flow of media throughout the system.

At low cell density intracellular gene activation is decreased as the AHL diffuses across the cell membrane and out of the chamber. At higher cell densities, the increased production of AHL in each cell acts to mitigate the outward flow such that activation of the genes can occur in a rhythmic fashion, and the observed colony-wide oscillations occur.

The video helped–didn’t it?

Do you know of other publications that were effectively complemented by the use of multimedia?

ResearchBlogging.org
Danino, T., Mondragón-Palomino, O., Tsimring, L., & Hasty, J. (2010). A synchronized quorum of genetic clocks Nature, 463 (7279), 326-330 DOI: 10.1038/nature08753

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Isobel Maciver

Isobel is a graduate of the University of Edinburgh and of Aston University in Birmingham, U.K. She is a technical writer and editor, and is also manager of the Scientific Communications group at Promega. She enjoys writing about issues in science and communication.

One thought on “Quorum Sensing in Bacteria: How a Picture can be Worth a Thousand Words

  1. Quorum…..”its related to density!!” Quorum sensing is a type of signalling process by which bacteria sense their population density and communicate with each other using species specific signalling molecules. This explains the dynamic nature of gene expression, and also tells us how bacterial gene expression get started after detecting the presence of Signal molecules in their zone / quorum.

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