A mathematical model for the growth process of the bacterium Bacillus subtilis is described. The model is a highly structured one. The driving motivation for development of the model and explicit accounting of major interactions of metabolic networks in the model is related to our eventual goal that the model will be used in the analysis of complex biological patterns. Bacillus subtilis was chosen in our study due to the interesting sporulation process that these cells undergo in response to adverse environmental conditions including nutrient limitation. Sporulation process in B. subtilis represents a primordial prototype of cellular differentiation in higher cellular systems. Thus a model for the B. subtilis growth process should prove extremely useful for understanding questions of developmental biology. The model is capable of simulating the transition between the exponential and stationary phase of growth in a batch culture. Since during the transition period the growth process and the metabolism become decoupled and many transient processes are taking place, such predictions are a severe test for the validity of any model. A strategy to examine the leading hypothesis on B. subtills sporulation implementing GTP as a component which signals sporulation initiation is described.
The effects of growth rate and substrate concentration on cellular metabolism of glucose was studied with cultures of B. subtilis 168. Application of chemostat culture techniques allowed for the observation of each growth condition independent of the other. The relative flux of carbon through biosynthetic and non‐biosynthetic pathways was determined by monitoring cell density and distribution of extracellular side products in active cultures. A metabolic shift of glucose utilization pathways was observed in cell cultures grown at dilution rates greater than 0.36 hr−1 or with glucose feed levels exceeding 10 gll. The predominant side products detected by HPLC analysis were acetic acid, formic acid, lactic acid, and acetoin. The patterns of side product formation were analyzed in relation to the applied growth conditions.
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