Sites of metal deposition in the cell wall of Bacillus subtilis

Amine and carboxyl groups of the cell wall of Bacillus subtilis were chemically modified individually to neutralize their electrochemical charge for determination of their contribution to the metal uptake process. Mild alkali treatment removed ca. 94% of the constituent teichoic acid (expressed as inorganic phosphorus) and allowed estimation of metal interaction with phosphodiester bonds. Chemical modifications of amine functions did not reduce the metal uptake values as compared to native walls, whereas extraction of teichoic acid caused a stoichiometric reduction in levels. In contrast, alteration of carboxyl groups severely limited metal deposition of most of the metals tested. X-ray diffraction and electron microscopy suggested, in this case, that the form and structure of the metal deposit could be different from that found in native walls. The observations suggest that carboxyl groups provide the major site of metal deposition in the B. subtilis wall.