Glutamate excretion triggering mechanism: a reinvestigation of the surfactant-induced modification of cell lipids.

Lipid alterations induced by surfactants to trigger glutamate excretion were investigated with an industrial strain of Corynebacterium glutamicum. The lipid composition of this strain was determined for cultures in a synthetic medium and in a complex medium. A distribution of complex lipids between the cell wall and the cell membrane is proposed. Depending on growth conditions, 70-85% of the cell fatty acids had saturated chains in cells grown with surfactants. In the synthetic medium up to 80% of the straight-chain fatty acids may have come from the acylated surfactant added to the induce excretion. In industrial fermentation, the maximal excretion rate corresponded to the highest saturated fatty acid content of cells. It was shown by radioactive labelling in the synthetic medium that the addition of the acylated surfactant induced the degradation of more than 50% of the phospholipids. Some phospholipid synthesis occurred at that time using the surfactant (saturated) fatty acids, but the membrane did nor recover its previous phospholipid content. A model is proposed to explain the mechanism of glutamate excretion triggering by surfactants.