Electrophoretic studies on bacteria. 3. The growth cycle of Bacillus megaterium, the behaviour of cells and the changes produced by lysozyme

Abstract

The changes in electro-phoretic behavior and susceptibility to lysozyme occurring during the growth cycle of B. megaterium in meat extract-peptone and in lactate-glucose media were studied. Parallel pH, electrical-conductivity and optical-density measurements were also made. Samples of vegetative cells were withdrawn from cultures of different ages; variations of the mobility with pH and the effect of lysozyme (which led to the production of protoplasts) were determined. The same pattern of electrophoretic change was observed during growth in both media. Little change in electrophoretic mobility occurred until the phase of rapid vegetative growth, when the mobility fell to a much lower value and thereafter remained constant up to and including the formation of spores, free of sporangia. After repeated washing, the spore behavior approximated that of the original spores. Lysozyme sensitivity was greatest for vegetative cells from young cultures and decreased with increasing age of the cultures. It was concluded that marked changes in surface composition occurred during the phase of rapid vegetative growth and that, whereas the composition of the cell walls remained constant thereafter, their thickness increased with age. From the variation of mobility with pH, the principal surface-charge group of vegetative cells appeared to be carboxyl, possibly associated with a hexosamine-peptide substance. The behavior of the protoplasts was consistent with that of a lipoprotein or protein surface.