The Catabolic Fate of Glucose in Bacillus subtilis

It has been shown by Gary and Bard (1) that the catabolic pathway of glucose in Bacillus subtilis changes with the cultural conditions, particularly the type of nitrogen source employed for the incubation. These authors reported that cells grown on tryptone-yeast extract-glucose medium (C-cells) rely heavily on the Embden-Meyerhof-Parnas pathway for glucose dissimilation, whereas cells grown on ammonium-salts-glucose medium (S-cells) utilize glucose predominantly via the hexose monophosphate pathway. The variation in catabolism has been explained by Gary, Klausmeier, and Bard (2) as due to the reduced levels of glyceraldehyde phosphate and lactate dehydrogenase present in S-cells and the absence of cytochrome oxidase in C-cells. The relative participation of catabolic pathways with respect to glucose utilization by B. subtilis cells grown on ammoniumsalts-glucose-yeast extract medium has subsequently been examined by Wang et al. (3). The results showed that under the described cultural conditions, glucose is catabolized mainly (65%) by way of the glycolytic pathway and to a limited extent (35%) via the hexose monophosphate pathway. Yet to be understood are several facets of the over-all catabolic mechanism. They are: (a) a quantitative evaluation of the variation in pathway participation as caused by changes in cultural conditions; (b) the fate of substrate glucose traversing the hexose monophosphate pathway, particularly with respect to the catabolic fate of fructose 6phosphate derived from substrate glucose. Better understanding of these facets is of great importance in evaluating the function of individual catabolic sequences with respect to respiration and synthesis and in elucidating the role played by the pentose cycle pathway in microbial catabolism. In this work, glucose and gluconate specifically labeled with Cl4 have been used as substrates for proliferating B. subtilis cells in a series of radiorespirometric studies. The findings provide much information with regard to the nature and function of the hexose monophosphate pathway in this organism. On the basis of an understanding reached in this study, the equations devised previously (3) for the estimation of glucose pathways in microorganisms have been modified.