Growth phases in batch

The models just discussed have a number of serious deficiencies, despite their being able to provide reasonable descriptions of certain phenomena in a limited number of cases. A most notable deficiency is their inability to predict a lag phase in batch growth. Consideration of this led Ramkrishna (R3) to develop new models in which microbial cultures are endowed with a certain amount of biochemical structure although these models are distributed rather than segregated, so that phenomena associated with reproduction cannot be treated, the models do predict qualitatively a number of phenomena that cannot be touched by unstructured models. 

Secondary metabolism is a form of differentiation, but cells grown in vitro are rapidly dividing, undifferentiated cells. Only at the end of the growth phase of batch-cultured cells may some form of differentiation occur, connected with the production of secondary metabolites. A plant produces a wide variety of secondary metabolites, all with different, mostly unknown functions. In in vitro cultured cells those compounds which defend the plant against microorganisms, namely, phytoalexins, are often easily formed. For example. Cinchona cell cultures produce large amounts of anthraquinones, but the alkaloids of interest, the quinolines, are produced in trace amounts only. Similarly Papaver cell cultures produce sanguinarine and closely related alkaloids, but no morphinane alkaloids. 

Figure 20.6 Different phases of a cell s growth cycle in batch culture...

Batch fermentation is the most widely used method of amino add production. Here the fermentation is a dosed culture system which contains an initial, limited amount of nutrient. After the seed inoculum has been introduced the cells start to grow at the expense of the nutrients that are available. A short adaptation time is usually necessary (lag phase) before cells enter the logarithmic growth phase (exponential phase). Nutrients soon become limited and they enter the stationary phase in which growth has (almost) ceased. In amino add fermentations, production of the amino add normally starts in the early logarithmic phase and continues through the stationary phase. 

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