Cell division in a species of Erwinia. XII. A study of nutritional influences in D-serine inhibition of growth and division of Erwinia sp., and of certain specific sites of D-serine action.

Abstract

D-Serine-induced inhibitions of growth and cell division of Erwinia sp. are greatly influenced by the pH and composition of the medium. In a glucose-aspartic medium, optimum elongation occurs at pH 6.8–7.2. In an aspartic acid medium, glucose, independently of pH, enhances division inhibition, but reduces growth inhibition. In ammonia media, a high toxicity is generally accompanied by poor inhibition of division. Division inhibition in ammonia media increases with decreasing ammonia concentration, and with increasing pantothenate concentration. Growth inhibition and division inhibition can, to a large extent, be varied independently of one another. Because of the nutritional dependence of division inhibition, it is proposed that the primary mechanism controlling the rate of division with respect to the rate of growth, and hence cell length, is at the metabolic level.D-Serine causes a marked accumulation of keto acids in most ammonia media as well as in a glucose – aspartic acid medium. This accumulation, decreased by added pantothenate, is the result of inhibition of pantothenate synthesis. D-Serine inhibits the entry of aspartic acid into the cell; this is a major factor in D-serine inhibition of growth. Filaments grown in the presence of D-serine show no decrease relative to normal cells in content of DNA, RNA, or protein.