Measurements of Free-swimming Speed of Motile Salmonella Cells in Liquid Media   

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Original research article

A brief version of this protocol appeared in:
PLOS Pathogens
Mar 2016


Bacteria such as Escherichia coli and Salmonella enterica swim in liquid media using the bacterial flagella. The flagellum consists of the basal body (rotary motor), the hook (universal joint) and the filament (helical screw). Since mutants with a defect in flagellar assembly and function cannot swim smoothly, motility assay is an easy way to characterize flagellar mutants. Here, we describe how to measure free-swimming speeds of Salmonella motile cells in liquid media. Free-swimming behavior under a microscope shows a significant variation among bacterial cells.

Keywords: Bacterial flagella, Motility, Motor, Optical microscopy, Proton motive force, Salmonella


The flagellar motor of E. coli and Salmonella is powered by downhill proton translocation along proton motive force (PMF) across the cytoplasmic membrane (Morimoto and Minamino, 2014; Minamino and Imada, 2015). The rotational speed of the proton-driven flagellar motor is proportional to total PMF (Gabel and Berg, 2003). Therefore, measurements of free-swimming speeds of motile cells allow us not only to analyze motor performance of various mutants but also to examine whether there is a significant difference in total PMF under experimental conditions (Minamino et al., 2016).

Copyright: © 2017 The Authors; exclusive licensee Bio-protocol LLC.
How to cite:  Readers should cite both the Bio-protocol article and the original research article where this protocol was used:
  1. Morimoto, Y. V., Namba, K. and Minamino, T. (2017). Measurements of Free-swimming Speed of Motile Salmonella Cells in Liquid Media. Bio-protocol 7(1): e2093. DOI: 10.21769/BioProtoc.2093.
  2. Minamino, T., Morimoto, Y. V., Hara, N., Aldridge, P.D. and Namba, K. (2016). The bacterial flagellar type III export gate complex is a dual fuel engine that can use both H+ and Na+ for flagellar protein export. PLoS Pathog 12(3): e1005495.

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