Chemical and ultrastructural examination of lead-induced morphological convertants of Bacillus subtilis.

Actively-growing Bacillus subtilis 168 cells, exposed to lead nitrate, had only slightly decreased ability to bind the divalent cation magnesium. The nature and quantity of the major cell wall metal binding components, teichoic and teichuronic acids, and the carbohydrate constituents of the peptidoglycan remained relatively constant. Purified cell walls, isolated from cells exposed to lead for 6 and 13 days, retained 9.9 micrograms Pb+2 and 3.5 micrograns Pb+2/mg cell wall, respectively. The occurrence of this lead in the isolated cell wall did not interfere with its Mg2+-binding capacity. While cationic binding properties, growth rate and cell yield indicated non-interference from lead, light and electron microscopic studies clearly demonstrated morphological alterations in approx. 30--50% of the lead treated cells. These alterations included the conversion to irregular spherical forms, some of which contained thickened cell walls. These anomalies are virtually identical to those reported for mutants of this bacterium derived via the introduction of classical mutagens. Protoplasts, similar to those produced by antibiotic and enzymatic treatments, were also present in the lead-treated cells. Although the most tenable explanation appeared to be cellular mutations, the morphological convertants appear to be derived from lead's interference with cell wall biosynthesis process and/or the assemblage of cell wall subunits.