BIOLOGY Volume 2 - A Guide to General Biology - 2004

12. MICROBIOLOGY AND BIOTECHNOLOGY

12.11. Medical Products

One of the most successful and economically lucrative sectors of the microbiological industry is the manufacturing of Pharmaceuticals. These products are typically effective in relatively small quantities and command a high market value. Producing them in bioreactors helps to reduce production costs. The following sections examine the most efficient Methods for pharmaceutical production.

12.11.1. Penicillin Production

The production of the antibiotic penicillin serves as a classic example of fed-batch cultivation used for secondary metabolite synthesis.

12.9. WHAT IS A) an antibiotic, b) fed-batch cultivation, c) a secondary metabolite?

Since its discovery in 1928 (section 12.10.2), penicillin has saved arguably millions of lives. It was first deployed on a large scale during World War II, primarily to treat soldiers suffering from Gonorrhea, a sexually transmitted infection. As the antibiotic became more widely available, it was applied to more life-threatening conditions, such as Pneumonia. Prior to the advent of Antibiotics, mortality rates from pneumonia reached as high as 30%. The MECHANISM OF ACTION of penicillin involves inhibiting Introduction/37.html">Bacterial Cell wall synthesis, particularly in Gram-positive Bacteria (section 2.3.1, cell wall). Only actively growing Cells are destroyed. Some bacteria harbor Plasmids that confer resistance to penicillin (section 2.3.1, plasmids). To date, several hundred types of penicillin have been identified, sharing a common core Structure but varying in their side chains. Some are natural, some synthetic, and others semi-synthetic. They exhibit varying degrees of Specificity—in other words, differing in their efficacy against various bacterial strains. This provides a strong incentive to continually search for alternative forms of the antibiotic.

Targeted screening for a suitable strain of the fungus Penicillium—the source of penicillin—was first initiated during the early years of World War II in the United States, even though Fleming discovered penicillin in England (from Penicillium notatum). The search was organized by Oxford University scientist Sir Howard Florey, backed by the extensive resources of the United States. Cultures and soil samples from all over the world were tested, but the highest yield was ultimately obtained from a strain of Penicillium chrysogenum isolated from a moldy cantaloupe purchased at a local market. Since then, through the Selection of high-yielding mutant strains and advancements in cultivation, extraction, and purification techniques, penicillin production yields have increased approximately 2,000-fold.

The COMPOSITION OF THE Fermentation medium is of critical importance. Glucose is the preferred carbon source; while it Supports fungal growth, it represses the Enzymes required for penicillin synthesis. Consequently, standard practice is to promote rapid fungal growth During the first 30–40 hours, followed by The addition of low concentrations of glucose either continuously or in controlled doses (i.e., fed-batch cultivation). Inexpensive Proteins, such as soybean or fish meal, serve as the nitrogen source. Additionally, phosphates, calcium carbonate, and phenylacetic acid are added to the medium to boost product yield, as they are essential precursors for the penicillin molecule. Because penicillin is a secondary metabolite, it is synthesized only after the initial, rapid growth phase. Primary metabolites, which are produced during this initial growth phase, include respiratory by-products such as carbon dioxide and ethanol.

The inoculum is prepared from fungal spores. Inoculating a 50,000 dm³ bioreactor requires 3 to 5 tons of mycelium. Because penicillin is demanded in massive quantities, production vessels with capacities of up to 200,000 dm³ have been constructed, consuming approximately 500 kg of glucose daily. Penicillin yield is highly Temperature-sensitive—temperatures can rise by up to 2 °C per hour—so this parameter must be closely monitored. The pH level must also be strictly regulated and maintained between 6.5 and 7.0. The entire fermentation cycle lasts approximately 15 days.

Downstream Processing begins with the removal of the mycelium via filtration, leaving the penicillin dissolved in the liquid phase of the culture medium. It is then extracted using a series of Solvents. Each extraction step removes a fraction of the impurities, progressively purifying the penicillin until it is dissolved in pure Water. The water is subsequently removed by vacuum evaporation, and the penicillin is crystallized as a sodium or potassium salt (penicillin itself being a weak acid).