Major sites of metal binding in Bacillus licheniformis walls

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Abstract
Isolated and purified walls of B. licheniformis NCTC 6346 his contained peptidoglycan, teichoic acid and teichuronic acid (0.36 .mu.mol of diaminopimelic acid, 0.85 .mu.mol of organic P and 0.43 .mu.mol of glucuronic acid/mg [dry weight] of walls, respectively). The walls also contained 0.208 .mu.mol of metal/mg. When these walls were subjected to metal-binding conditions for 9 metals [Na, K, Mg, Ca, Mn, Fe(III), Ni, Au], the amount of bound metal above background ranged from 0.910 .mu.mol of Na to 0.031 .mu.mol of Au/mg of walls. Most were in the 0.500 .mu.mol mg-1 range. Electron-scattering profiles from unstained thin sections indicated that the metal was dispersed throughout the wall fabric. Mild alkali treatment extracted teichoic acid from the walls (97% based on P) but left the peptidoglycan and teichuronic acid intact. This treatment reduced their capacity for all metals but Au. Thin sections revealed that the wall thickness had been reduced by 1/3 but metal was still dispersed throughout the wall fabric. Trichloroacetic acid treatment of the teichoic acid-less walls removed 95% of the teichuronic acid (based on glucuronic acid) but left the peptidoglycan intact (based on sedimentable diaminopimelic acid). The thickness of these walls was not further reduced but little binding capacity remained (usually < 10% of the original binding). The staining of these walls with Au produced a 14.4-nm repeat frequency within the peptidoglycan fabric. Sedimentation velocity experiments with the extracted teichuronic acid in the presence of metal confirmed it to be a potent metal-complexing polymer. Thus, teichoic and teichuronic acids are the prime sites of metal binding in B. licheniformis walls.