Article
- The EMBO Journal (2005) 24, 2034 - 2042
- doi:10.1038/sj.emboj.7600668
Published online: 5 May 2005
Subject Categories:
Sensing wetness: a new role for the bacterial flagellum
Qingfeng Wang1, Asaka Suzuki1, Susana Mariconda1, Steffen Porwollik2 and Rasika M Harshey1
- Section of Molecular Genetics and Microbiology & Institute of Cellular and Molecular Biology, University of Texas at Austin, Austin, TX, USA
- Sidney Kimmel Cancer Center, San Diego, CA, USA
Correspondence to:
Rasika M Harshey, Section of Molecular Genetics and Microbiology & Institute of Cellular and Molecular Biology, University of Texas at Austin, Austin, TX 78712, USA. Tel.: +1 512 471 6881; Fax: +1 512 471 7088; E-mail: rasika@uts.cc.utexas.edu
Received 10 February 2005; Accepted 11 April 2005
Abstract
We have uncovered a new role for the bacterial flagellum in sensing external wetness. An investigation into why mutants in the chemotaxis signaling pathway of Salmonella typhimurium exhibit fewer and shorter flagella than wild-type when propagated on a surface, first showed that the mutants downregulate only a small set of genes on swarm media—class 3 or 'late' motility genes, and genes associated with the pathogenicity island SPI-1 TTSS (type three secretion system). Based on observations that swarm colonies of the mutants appear less hydrated, we tested a model in which the flagellum itself is a sensor: suboptimal external hydration interferes with secretion of flagellin subunits, inhibiting filament growth and blocking normal export of the class 3 transcription inhibitor FlgM. We provide strong experimental support for the model. In addition, the data show that the flagellar and SPI-1 TTSS are coupled via regulatory proteins. These studies implicate the flagellum, a bacterial organ for motility, in sensing the external environment to modulate not only its own biogenesis but other physiological functions as well.
Keywords:
- chemotaxis signaling pathway,
- flagella biogenesis,
- flagellum as sensor,
- Salmonella pathogenicity island,
- swarming motility
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