Nutrient-rich medium

The process of serum-free adaptation of cells currently grown in serum begins with selecting a serum batch that supports growth of the cells in low serum concentrations and selecting a rich nutrient medium that supports cell proliferation in low serum. 

The population size of bacteria and unicellular algae as a function of time in a growth culture is illustrated by Figure 11.12, which shows a population curve for a bacterial culture. Such a culture is started by inoculating a rich nutrient medium with a small number of bacterial cells. Bacteria multiply exponentially in the log phase. 

Nutritional Requirements. The nutrient requirements of mammalian cells are many, varied, and complex. In addition to typical metaboHc requirements such as sugars, amino acids (qv), vitamins (qv), and minerals, cells also need growth factors and other proteins. Some of the proteins are not consumed, but play a catalytic role in the cell growth process. Historically, fetal calf semm of 1—20 vol % of the medium has been used as a rich source of all these complex protein requirements. However, the composition of semm varies from lot to lot, introducing significant variabiUty in manufacture of products from the mammalian cells. 

Microbial insecticides are very complex materials in their final formulation, because they are produced by fermentation of a variety of natural products. For growth, the bacteria must be provided with a source of carbon, nitrogen, and mineral salts. Sufficient nutrient is provided to take the strain of choice through its life cycle to complete sporulation with concomitant parasporal body formation. Certain crystalliferous bacilli require sources of preformed vitamins and/or amino acids for growth. Media for growing these bacilli may vary from completely soluble, defined formulations, usable for bench scale work, to rich media containing insoluble constituents for production situations (10,27). Complex natural materials such as cottonseed, soybean, and fish meal are commonly used. In fact, one such commercial production method (25) is based on use of a semisolid medium, a bran, which becomes part of the final product. 

Several studies were performed on the optimization of expression levels of ELP proteins in E. coli. In a recent example, the expression protocol was optimized for an ELP fusion with green fluorescent protein (GFP). This fusion protein was expressed and purified in a yield of 1.6 g/L of bacterial culture, which finally yielded 400 mg GFP/L bacterial culture. This extremely high yield was found after uninduced expression in nutrient-rich medium supplemented with phosphate, glycerol and certain amino acids, such as proline and alanine [234]. The influence of fusion order was also examined and it was found that positioning the ELP at the C-terminus of target protein resulted in significantly higher expression levels [35]. 

Enzyme Production. P. sajor-caju, when grown in a nutrient-rich medium under aerated, agitated conditions, was able to mineralize partially 14C-DHP lignin, as shown in Figure 1 (25). 

To understand the special constraints of herbivorous fishes, it helps to first understand the carnivore digestive process.40412 Carnivorous fishes consume food in which nutrients are generally readily available and of high quality (protein rich). In these fishes, food is usually broken down in the stomach through a combination of muscular contractions of the stomach wall and enzymatic action in an acid medium. Breakdown products are expelled from the stomach through the pyloric sphincter into the intestine in a process called gastric evacuation. Digestion and food absorption are completed in the intestine.40412... 

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