In recent years, a market surge in biopharmaceuticals has warranted extensive research and development in advanced cell culturing techniques and subsequent methods of optimizing bioprocesses. Media development is one of the most critical stages in biopharmaceutical manufacturing. Indeed media components have such a strong impact, they can account for up to 30% of the total production cost.1 This area of development offers the potential to dramatically improve yield and quality of the expressed product.2The ideal cell culture medium, whether for use in mammalian or microbial systems, is one that provides process consistency, robustness, and batch-to-batch reproducibility. Essentially, a raw material must meet most, if not all, criteria listed below.3
For many years, economic constraints have dictated media composition. This has led to the widespread use of complex, readily available raw materials, making large-scale fermentations reliant on cheap sources of carbon and nitrogen, which are often by-products of other industries such as corn steep liquor from the corn-starch industry and beet molasses from the sugar industry. Combining such complex components with animal-derived hydrolysates has increased the scope of product manufacture, creating high yielding processes at minimal costs. The abundance of biosynthetic precursors and growth-promoting agents make complex media the composition of choice, primarily because they accelerate growth and enhance productivity. Complex raw materials usually are derived from animal-sourced processes, such as hydrolysed peptones and sera. They also may be non-animal–derived, such as the by-products beet molasses and corn steep liquor. They can contain numerous individual components, some of which are semi-characterized and many more are uncharacterized. In many cases, biomass yields are greater with complex and semi-defined media than with chemically defined media. However, data from physiological studies is more difficult to interpret and can be clouded or influenced by many intrinsic parameters.
Growth precursors found in such complex components may be channelled directly into anabolic pathways, thus saving metabolic energy.4 This offers an immediate advantage in terms of culture metabolism but ultimately makes process definition and development problematic.
Fermentations using complex media have worked successfully for many years, and strain selection is often based around current media and cultivation conditions. Media development, however, is largely empirical, with little research into defining such raw materials. For example, a modified strain of the yeast Saccharomyces cerevisiae, which had been labelled the ultimate solution to lignocellulose-derived xylose, was found to require yeast extract, additional hexose sugar, and oxygenation,5 thus making growth in a chemically defined media difficult without intensive investigation. Therefore, the final industrial environment must be considered to prevent unanticipated costs at later stages. Both S. cerevisiae and Escherichia coli have extensive biosynthetic capacity and can grow well in defined media. In contrast, the biosynthetic capacity of many lactic acid bacteria are limited and they require complex or extensively supplemented media for efficient growth.6
The quest for increased productivity combined with patient safety has encouraged biopharmaceutical companies to invest more time and money into their processes and for raw material suppliers to explore new chemically defined versions of media.