The interaction between electron transfer, proton motive force and solute transport in bacteria

Abstract

The properties of proton solute symport have been studied in Streptococcus cremoris, Rhodopseudomonas sphaeroides and Escherichia coli. In the homolactic fermentative organism S. cremoris the efflux of lactate is a membrane protein-mediated process, which can lead to the generation of a proton motive force. These observations support the energy-recycling model that postulates the generation of metabolic energy by end-product efflux. Studies with oxidants and reductants and specific dithiol reagents in E. coli membrane vesicles demonstrated the presence of two redox-sensitive dithiol-disulphide groups in the transport proteins of proline and lactose. The redox state of these groups is controlled by the redox potential of the environment and by the proton motive force. One redox-sensitive group is located at the inner surface, the other at the outer surface of the membrane. In Rps. sphaeroides and E. coli the activity of several transport proteins depends on the activity of the electron transfer systems. On the basis of these results a redox model for proton solute transport coupled in parallel to the electron transfer system is postulated.

Molecular mechanisms of inhibiting glucosyltransferases for biofilm formation in Streptococcus mutans

“…The proton motive force consists of two gradients: an electrical potential (Δψ, positive outside / negative inside ) and a chemical transmembrane gradient of protons (ΔpH, acidic outside /alkaline inside ). [89][90][91][92] Enzyme secretion by bacterial cells, in general, is coupled to the proton motive force. Some drugs can reduce the proton motive force by enhancing proton permeability and discharging ΔpH across the cell membrane; [93][94][95] thus, the side effects and selectivity are not defined.…”

Transport of Sugars

“…The first experimental evidence for proton cotransport-again with the lactose transport system (35)-was published in 1970 and, for the first eukaryotic cell, in 1973 (36,37). Subsequently, it rapidly became clear that H + symport or cotransport is a major transport mechanism for bacteria, fungi, and plants (38)(39)(40), whereas in animals, sodium is the cotransported ion (41,42). Responsible for maintaining the gradient are the H + -and Na + /K + -ATPases.…”

The death and lysis of microorganisms in environmental processes

“…More recently, Michels et al [120] have described an 'energy recycling model' which in essence is the reverse process of secondary transport of solutes, whereby the energy of an electrochemical product gradient is converted into the energy of an electrochemical proton gradient. Such systems have been detected in the homolactic fermentative Streptococcus cremoris and in Escherichia coli when the microbes are growing fermentatively and therefore have no means for proton extrusion by functional electron transport systems [121].…”