Chemotactic signaling in filamentous cells of Escherichia coli

Abstract

Video techniques were used to record chemotactic responses of filamentous cells of Escherichia coli stimulated iontophoretically with aspartate. Long, nonseptate cells were produced from polyhook strains either by introducing a cell division mutation or by growth in the presence of cephalexin. Markers indicating rotation of flagellar motors were attached with anti-hook antibodies. Aspartate was applied by iontophoretic ejection from a micropipette, and the effects on the direction of rotation of the markers were measured. Motors near the pipette responded, whereas those sufficiently far away did not, even when the pipette was near the cell surface. The response of a given motor decreased as the pipette was moved away, but it did so less steeply when the pipette remained near the cell surface than when it was moved out into the external medium. This shows that there is an internal signal, but its range is short, only a few micrometers. These experiments rule out signaling by changes in membrane potential, by simple release or binding of a small molecule, or by diffusion of the receptor-attractant complex. A likely candidate for the signal is a protein or ligand that is activated by the receptor and inactivated as it diffuses through the cytoplasm. The range of the signal was found to be substantially longer in a cheZ mutant, suggesting that the product of the cheZ gene contributes to this inactivation.

In vitro Approach to Bacterial Chemotaxis

“…As a matter of fact, many of the CheY batches were never active. We do not known the cause of this lack or loss of activity, but it is in accordance with the observations of Segall et al (1985), who found that the signal molecule, possibly CheY, is quickly inactivated within the cell. It appears that there should be another substance in the cell for activation ofCheY.…”

Reaction‐Diffusion Systems in Intracellular Molecular Transport and Control

“…In contrast, binding of attractants to the receptor prevents autophosphorylation of CheA and activation of CheY-consequently, the bacterium swims straight toward the increasing concentration of attractant. In these processes, the response time of the flagella-that is, the time required for CheY to diffuse from the receptor site to the motor and to subsequently associate with this motor-has been measured experimentally to be 50-200 ms. [98,99] These values are close to the theoretical estimate of the characteristic time for the two-dimensional diffusion of t D~L 2 /D, which for the diffusion of a small protein such as CheY through the cytoplasm is 100 ms (assuming L = 1 mm and the diffusion coefficient D = 1 10 À7 cm 2 s À1 for CheY [72,100] ). The rate constant for the CheY-motor association is k % 3 10 6 m À1 s À1 [101,102] and the average concentration of CheY in the cell is approximately 3 mm, [103] which gives the characteristic reaction times (t R~1 /kc CheY for species reacting according to a second-order kinetics) for CheY-motor association also on the order of 100 ms.…”

The use of flash photolysis for a high‐resolution temporal and spatial analysis of bacterial chemotactic behaviour: CheZ is not always necessary for chemotaxis

“…4) but at a very slow rate. The long latency of cheZ null mutants' response (specifically an aspartate-induced reversal of flagellar rotation) was noted by Segall et al (1985). We interpret this sluggish response to reflect the rate of autodephosphorylation of CheY in the absence of CheZ.…”