Estimates of the porosity of Bacillus licheniformis and Bacillus subtilis cell walls.

The maximum porosity of Bacillus subtilis and Bacillus licheniformis cell walls was estimated by two independent and relatively simple methods. Peptidoglycan was isolated from Bacillus subtilis cell wall preparations and used as an insoluble support for exclusion chromatography of dextrans of known average molecular size. In an alternative approach the leakage of radioactively labelled proteins from Bacillus licheniformis cells incubated in butanol-saline mixtures was measured and their size estimated by exclusion chromatography on Sephadex G-100. Under these conditions the permeability barrier of the cytoplasmic membrane was destroyed with preservation of the structural integrity of the outer cell wall. The apparent exclusion threshold of the cell wall of either organism as determined by these means corresponded to molecules with a diffusional radius of not more than 2.5 nm.