This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Khan, S. Articles by Trentham, D. R. Search for Related Content PubMed PubMed Citation Articles by Khan, S. Articles by Trentham, D. R.

The Fast Tumble Signal in Bacterial Chemotaxis

Shahid Khan ^*, Sanjay Jain , Gordon P. Reid  and David R. Trentham 

^* Molecular Biology Consortium, Chicago, Illinois; Department of Physics and Astrophysics, University of Delhi, Delhi, India; and National Institute for Medical Research, London, United Kingdom

Correspondence: Address reprint requests to Shahid Khan, Tel.: 312-829-4184; E-mail: kh01{at}tigger.uic.edu.

We have analyzed repellent signal processing in Escherichia coli by flash photorelease of leucine from photolabile precursors. We found that 1), response amplitudes of free-swimming cell populations increased with leucine jump concentration, with an apparent Hill coefficient of 1.3 and a half-maximal dose of 14.4 µM; 2), at a 0–0.5 mM leucine concentration jump sufficient to obtain a saturation motile response, the swimming cell response time of 0.05 s was several-fold more rapid than the motor response time of 0.39 ± 0.18 s measured by following the rotation of cells tethered by a single flagellum to quartz coverslips; and 3), the motor response time of individual cells was correlated with rotation bias but not cell size. These results provide information on amplification, rate-limiting step, and flagellar bundle mechanics during repellent signal processing. The difference between the half-maximal dose for the excitation response and the corresponding value reported for adaptation provides an estimate of the increase in the rate of formation of CheYP, the phosphorylated form of the signal protein CheY. The estimated increase gives a lower limit receptor kinase coupling ratio of 6.0. The magnitude and form of the motor response time distribution argue for it being determined by the poststimulus switching probability rather than CheYP turnover, diffusion, or binding. The temporal difference between the tethered and swimming cell response times to repellents can be quantitatively accounted for and suggests that one flagellum is sufficient to cause a measurable change of direction in which a bacterium swims.