The assimilation of amino-acids by bacteria; action of inhibitors on the accumulation of free glutamic acid in Staphylococcus aureus and Streptococcus faecalis.

Certain Gram-positive bacteria have the ability to concentrate certain amino-acids in the free state within the cell (Gale, 1947; Taylor, 1947). Aminoacids may pass across the cell wall either by a process of diffusion, as in the case of lysine which becomes concentrated within the cell by a form of Donnan effect (Najjar & Gale, 1950), or as a result of an active transfer which requires energy obtained from exergonic metabolism such as fermentation. Glutamic acid does not enter either Staphylococcus aureuw (Micrococcus pyogenes var. aureus) or Streptococcus faecalis unless these organisms are metabolizing glucose, but the mechanism of this 'energylinked' transfer across the cell wall is not yet known. Gale & Mitchell (1947) showed that the concentration of the free amino-acid within the cell is determined by the balance between the rate of passage into the cell and the rate of metabolism within the cell; thus a substance such as crystal violet which inhibits the internal metabolism of glutamic acid in Strep. faecalis increases the steady state concentration of free glutamic acid within the cell, while treatment of the cell with penicillin (Gale & Taylor, 1947) inhibits the passage of glutamic acid into Staph. aureus so that the internal concentration decreases until exhausted by internal metabolic processes. The passage of glutamic acid into Staph. aureus is also inhibited by 8-hydroxyquinoline which appears to act by chelation ofa metal essential to the process; deprivation experiments show that the transfer is activated by manganese, although this can be replaced by magnesium in higher concentration (Gale, 1949). Clifton (1946) has shown that oxidative assimilation ofcarbon substrates in Gram-negative organisms is inhibited by sodium azide or 2:4-dinitrophenol. These, together with arsenate, appear to act by uncoupling the generation of energy-rich phosphate bonds from oxidative processes (Needham & Pillai, 1937; Loomis & Lipmann, 1948; Cross, Taggart, Covo & Green, 1949). Spiegelman, Kamen & Sussman (1948) have shown that sodium azide prevents the transfer of inorganic phosphate to the organic fraction accompanying the coupled oxidation ofglyceraldehyde phosphate. The present communication reports the action of these inhibitors on the accumulation of free glutamic acid within Staph. aureu8 and Strep. faecalis. During the course of the work it became clear that the process involved in the passage of glutamic acid into Staph. aureus has properties and sensitivities to inhibitors different from those of the similar process in Strep. faecalis. This can be correlated with differences previously noted in the quantitative aspect of the internal metabolism of glutamic acid (Gale & Rodwell, 1949) and in the conditions controlling the diffusion of free glutamic acid out of the cells (Gale, 1948).