Abstract
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.
Highlights
The catabolism of glucose and gluconate in Bacillus subtilis cells grown on different media has been studied by means of the radiorespirometric method
Regardless of the nature of the cultural medium, glucose appears to be catabolized by the concurrent operation of the glycolytic (Embden-Meyerhof-Parnas) and the hexose monophosphate (HMP) pathways
Fructose 6-phosphate is in turn catabolized in a manner identical with that of the substrate glucose, i.e. mainly by way of the glycolytic pathway and to a minor extent via the HMP pathway
Summary
Two types of cells were used: complex cells (C-cells) grown on a complex medium containing 1% Bacto yeast extract, 1% Bacto tryptone, 0.5% K2HP04, and 1% glucose; and simple cells (S-cells) grown on a simple medium containing (in grams): NH&I, 2.0; KHzP04, 0.9; K2HPOI, 4.65; MgS04.7Hz0, 0.2; NaCl, 0.01; FeS04.7Hz0, 0.01; MnS04. Cells were grown in either the complex medium or the simple medium at 37” under aerobic conditions. The cell crop was harvested by centrifugation and immediately resuspended in glucose-free medium, otherwise identical with the respective growth medium, to a concentration of 1 mg per ml for the radiorespirometric experiments. Glucose-l-, -2-, -3-, and &Cl4 were obtained from the National. Glucose-3,4-04 was prepared in this laboratory according to the method of Wood, Lifson, and Lorbes [4]. Gluconatel-U4 was obtained from Nuclear Chicago Corporation
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