Function of teichoic acids and effect of novobiocin on control of Mg2+ at the bacterial membrane.

Abstract

ALTHOUGH the occurrence of both wall and membrane teichoic acids in Gram-positive bacteria has been known for a considerable time and it is believed that they are essential for normal cellular activity, their main function has been somewhat obscure. Confirmatory evidence for the proposal1 that teichoic acids participate in ion-exchange in the outer regions of the bacterial cell has been described recently2. It has been shown that the phosphate groups of the wall teichoic acid are responsible for the capacity of isolated walls to bind magnesium ions; but whole cells of Gram-positive bacteria also invariably contain a poly-glycerol phosphate-teichoic acid located in the region between the wall and the cytoplasmic membrane3 and it is believed that this must be able to bind Mg2+ as does the wall polymer. These two regions of anionic polymer might thus constitute an integrated cation-exchange system between the exterior of the cell and the cytoplasmic membrane, where relatively high concentrations of Mg2+ are required for a variety of processes. We report here experiments with a membrane-bound enzyme system that requires Mg2+, obtained from a broken cell preparation and in which the close contact between the outer layers of the cell is preserved. In this preparation the enzyme system displays maximum activity in the presence of Mg2+ bound to the endogenous teichoic acid and is insensitive to changes in the concentration of added Mg2+, in marked contrast to the behaviour of the enzyme system in isolated cytoplasmic membrane. These results provide the first direct demonstration of the function of teichoic acids in concentrating Mg2+at the cytoplasmic membrane. They lead to the conclusion that failure of teichoic acid biosynthesis in the whole cell would cause inhibition of membrane function through magnesium starvation. In view of this the effect of novobiocin, an antibiotic shown to inhibit teichoic acid biosynthesis in vitro4–6, is discussed.