Distinction between changes in membrane potential and surface charge upon chemotactic stimulation of Escherichia coli

Abstract

Galactose and other chemotactic attractants have been shown to trigger an apparent hyperpolarization in Escherichia coli (Eisenbach, M., 1982, Biochemistry, 21:6818-6825). The probe used to measure membrane potential in that study, tetraphenylphosphonium (TPP+), may respond also to surface-charge changes in the membrane. The distinction between true changes in membrane potential and changes in the surface charge of the membrane is crucial for the study of this phenomenon in bacterial chemotaxis. To distinguish between these parameters, we compared the response to galactose with different techniques: K+ distribution in the presence of valinomycin (measured with a K+-selective electrode), TPP+ distribution (measured with a TPP+-selective electrode) at different ionic strengths, absorbance changes of bis(3-phenyl-5-oxoisoxazol-4-yl)pentamethineoxonol (oxonol V), and fluorescence changes of three probes with different mechanisms of response. All the techniques revealed stimulation by galactose of transient hyperpolarization, of comparable magnitude. This indicates the involvement of ion currents rather than alterations of local surface properties.

Voltage clamp effects on bacterial chemotaxis

“…Since in the absence of K+ valinomycin does not affect the PMF (3,17,47) or the swimming behavior of the bacteria (Table 4), it was hoped that in the presence of only 2 mM K+ (lower than the presumed internal concentration [6]) valinomycin would clamp Atwithout dissipating it. This was the observed result (Table 4).…”

“…The statistical significance of the change in adaptation time in high-K+ buffer (Table 3) or with B. subtilis was, however, doubtful (P s 90%). Since the average change in adaptation time was only 24%, it seems to us that this change may be the consequence of a secondary or an indirect effect of A%s on one of the processes involved in adaptation, e.g., the chemotaxis-related hyperpolarization (12,13,15,17) (cf. Fig.…”

Role of proton motive force in phototactic and aerotactic responses of Rhodopseudomonas sphaeroides

“…itself, however, that causes the tactic signal but instead it is the consequent increase in pmf. The primary signal involved in the chemotactic response is still unknown, but there is some evidence that there is a change in pmf on binding of the chemoeffector to the receptor in some bacterial species (2,8,9), although the evidence is conflicting and the time course of the chemotactic response suggests an additional requirement (16,17). We currently are investigating the interaction of chemotaxis and the electron transport taxes to identify the mechanism of interaction.…”

Sexual hormones: Effects on cardiac and mitochondrial activity after ischemia–reperfusion in adult rats. Gender difference

“…To analyze changes in the transmembrane potential, we used tetraphenylphosphonium (TPP), as described by Eisenbach et al [15].…”