X-ray Photoelectron Studies of Magnesium Ions bound to the Cell Walls of Gram-positive Bacteria

Abstract

TEICHOIC acids are strongly acidic polymers containing phosphate, which are present in all Gram-positive bacteria¹. They are found at two distinct locations in the cell envelope: associated with a glycolipid on the outer surface of the cytoplasmic membrane^2,3 and covalently linked to the peptido-glycan of the cell wall³. The wall teichoic acid is responsible for the ability of the cell walls of Gram-positive bacteria to bind divalent cations⁴ and the membrane teichoic acid mediates an interaction between magnesium ions, bound to the wall, and the cytoplasmic membrane, thus maintaining the optimum cation environment for the activity of magnesium-dependent biosynthetic enzymes in the membrane^5,6. It is therefore important to identify the interactions involved in binding magnesium to teichoic acids in the bacterial envelope; although electrostatic interaction between the cations and negatively charged phosphate groups is a prominent feature, interactions with other components of the envelope cannot be ruled out. For example, the amount of D-alanine esterified to the wall teichoic acid of Staphylococcus aureus H and Micrococcus sp. 24 influences the capacity of these walls to bind Mg²⁺ (ref. 4).