Mechanisms of Energy Coupling to the Transport of Amino Acids by Staphylococcus aureus

Abstract

Wc have studied the effect of artifically imposed transmembrane pH gradients on the uptake of amino acids by Staphylococcus aureus.I n high potassium medium, cells treated with valinomycin and tetrachlorosalicylanilide and at Donnan equilibrium, were found to accumulate glutamate.I n low potassium medium, addition of acid to the extracellular environment was found to stimulate the uptake of glutamate and aspartate, to induce partial lysine efflux, and to cause a small and transient isoleucine uptake.I n conjunction with earlier data from this laboratory (1973), it is concluded that the basic, neutral and acidic amino acids behave, respectively, as cationic, uncharged and anionic substrates, accumulating in Staphylococcus aureus in response to (a) the membrane potential, inside negative, (b) the total protonmotive force, and (c) the transmembrane pH gradient, inside alkaline.I n previous papers [1,2] we presented evidence in favour of the hypothesis that lysine is transported in Staphylococcus aureus by means of a uniport mechanism, the monovalent cation being translocated in response to the membrane potential, inside negative. By inducing potassium efflux on the addition of valinomycin [2], we further obtained data which allowed the conclusion to be drawn that the accumulation of glycine and isoleucine is dependent on the total protonmotive force, these amino acids being transported most likely by means of protoncoupled symporters which recognise the uncharged forms of these amino acids, Such valinomycin treatment was found to have no effect on the characteristics of glutamate uptake. This negative result was, howevcr, in keeping with the previous suggestion [l] that acidic amino acids may also be translocated by means of proton-coupled symporters displaying a stoichiometry of 1 : I with respect to proton and the monovalent amino-acid anions. According to this hypothesis, the translocation of acidic amino acids would be electroneutral and dependent only on the transmembrane pH gradient, inside alkaline.I n this present investigation we set out to test this hypothesis directly. Through altering the transmembrane pH gradient by experimental manipulation of' the extracellular ionic environment, we have examined the uptake of acidic, and additionally of neutral and basic amino acids, in response to this artificially imposed driving force. We have been able to confirm the proposed role of the transmembrane pH gradient in the uptake and accumulation of amino acids by Staph. aureus. MATERIALS AND METHODS Preparation of Cell XuspensionsSuspensions of endogenously reduced Staphylococcus aureus (Colworth bacterial culture collection 273) were routinely prepared as described previPotassium-depleted cells were prepared similarly, except in the final resuspension; cells from a 100 ml culture were resuspended in 75 ml 0.25 mM N-tris-(hydroxymethyl) -methyl -2 -aminoethane -sulphonic acid, 0.1 mM Tris, p H 7 .O. Tetrachlorosalicylanilide and valinomycin (in 36 p1 volumes of acetone) were added to 1.4 pM and 1.8 pM, respectivel...

Aminoglycoside-resistant mutants of Pseudomonas aeruginosa deficient in cytochrome d, nitrite reductase, and aerobic transport

“…This is consistent with PAO 2403's having a reduced electrical potential (,lP) component of the proton motive force (12). Transport of glutamic acid has been reported in some bacteria (11) to be driven mainly by the ApH component of the proton motive force, and its transport rate is normnal. This is fully consistent with previous data supporting the proposal that aminoglycosides act as polycations and their transport is driven by AA' (4).…”

A PBP 2 Mutant Devoid of the Transpeptidase Domain Abolishes Spermine–β-Lactam Synergy in Staphylococcus aureus Mu50

“…It is known that the transmembrane pH gradient is essential for the uptake of amino acids in S. aureus (24). The ability of MuM to adjust the transmembrane pH gradient may be reduced due to the PBP 2 mutation and concurrent cell wall anomaly, which could be a possible reason for its reduced growth rate when the pH is lower than 7.…”

Lysine uptake and exchange in Corynebacterium glutamicum

“…Thus, the most simple uptake mechanism for lysine in bacteria would be the uptake of this cationic amino acid driven by the membrane potential according to a uniport mechanism. This in fact takes place in several cases, for example in Staphylococcus aureus (19) and Escherichia coli (20). However, a variety of other transport mechanisms have also been described for lysine uptake in different bacteria.…”