Variation in swimming speed of Escherichia coli in response to attractant
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ORIGINAL PAPER
Variation in swimming speed of Escherichia coli in response to attractant Deepti Deepika · Richa Karmakar · Mahesh S. Tirumkudulu · K. V. Venkatesh
Received: 23 July 2014 / Revised: 4 September 2014 / Accepted: 19 September 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract It is well known that Escherichia coli executes chemotactic motion in response to chemical cues by modulating the flagellar motor bias alone. However, previous studies have reported the possibility of variation in run speed in the presence of attractants although it is unclear whether bacteria can deliberately modulate their swimming speeds in response to environmental cues or if the motor speeds are hardwired. By studying the detailed motion of cells in a uniform concentration of glucose and its nonmetabolizable analogue, we show that changing concentrations may be accompanied by variation in the swimming speed. For a fixed run duration, cells exposed to the attractants achieved a higher peak-swimming speed after a tumble compared with that in plain motility buffer. Our experiments using the mutant strain lacking the Trg sensor show no change in swimming speed with varying concentrations of the non-metabolizable analogue, suggesting that sensing may play a role in the observed variation of swimming speed.
Communicated by Erko Stackebrandt. Deepti Deepika and Richa Karmakar have contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00203-014-1044-5) contains supplementary material, which is available to authorized users. D. Deepika · R. Karmakar · M. S. Tirumkudulu (*) · K. V. Venkatesh Department of Chemical Engineering, IIT Bombay, Mumbai 400076, India e-mail: [email protected] K. V. Venkatesh e-mail: [email protected]
Keywords Chemotaxis · Bacterial motility · Bacterial motor · Escherichia coli
Introduction It is well known that Escherichia coli achieves chemotaxis through a biased motion by changing the rotational direction of its individual flagellum (Adler 1966; Berg and Brown 1972; Macnab and Koshland 1972; Larsen et al. 1974; Eisenbach 2004; Berg 2004; Wadhams and Armitage 2004). A counterclockwise (CCW) rotation bundles the flagella to provide thrust and results in a run, while a clockwise (CW) rotation of one or more flagella unbundles the flagella to give a new random direction called a tumble. To achieve a net drift toward a favorable attractant or away from a repellent, the cell modulates the duration of the motor bias and therefore the duration of run and tumble via a well-characterized signaling pathway. Single cell studies have thus demonstrated that the drift velocity is achieved by modulating the motor bias alone while keeping the run speed constant (Larsen et al. 1974; Berg 2004). However, a few studies have reported the possibility of variation in run speed in the presence of attractants (Berg and Brown 1972; Gabel and Berg 2003; Ahmed and Stocker 2008; Vuppala et al. 2010). Therefore, it is unclear whether bacteria can deliberate
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