Biotechnology - Yu.O. Sazykin 2006

General Biotechnology
Main Stages of the Biotechnological Process
Biosynthesis Process. Classification by Technological Parameters

The central process of biotechnological manufacturing—Biosynthesis in a fermenter—is typically characterized using various criteria.

Most frequently, it is differentiated According to the material flow Organization principle into batch, semi-batch (or fed-batch), continuous, draw-and-fill, and multi-cycle processes.

Based on the cultivation pattern of the producer, the biosynthesis process is divided into surface and submerged fermentations.

According to the type of target product, biosynthesis yields biomass, high-molecular-weight individual substances (such as Enzymes, etc.), as well as low-molecular-weight Primary and secondary metabolites.

The batch process is relatively simple and quite commonly used; however, it cannot be considered optimal. In a batch process, all Components of the nutrient medium and the inoculum are loaded into the fermenter simultaneously. Once loaded, all peripheral piping elements of the fermenter are activated, and a complete Fermentation cycle takes place. Upon its completion, the culture liquid (along with the mycelium) is drained and sent to the chemical purification department to isolate the target product. Thus, no correction of biosynthesis conditions is performed during the fermentation cycle; there is neither constant Maintenance of the optimal ratio of carbon, nitrogen, and phosphorus sources, nor The addition of target product precursors at the right moment, nor the preservation of the optimal pH value, and so on. All of this affects fermentation productivity, resulting in a lower yield of the target product.

The semi-batch (fed-batch) process is more advanced compared to the batch process. It improves producer growth and target product biosynthesis, and provides the opportunity to correct the process when it deviates from optimal conditions.

The continuous fermentation process involves the continuous withdrawal of small portions of the culture liquid from the fermenter while simultaneously introducing an equal volume of nutrient medium. This creates a flow-through system. The Use of a continuous process is advisable, for instance, when the target product is the biomass of the cultivated microorganism itself.

The draw-and-fill fermentation process is intermediate between batch and continuous processes. The culture liquid is withdrawn in larger portions than in a continuous process.

The multi-cycle process is yet another variant of batch fermentation. Upon completion of a fermentation cycle, when draining the culture liquid, approximately 10% of it is left in the apparatus; then 90% (by volume) of fresh nutrient medium is added to the fermenter, and a new fermentation cycle begins. Consequently, this process requires neither the cultivation of a new inoculum nor the Preparation and Sterilization of the fermenter and pipelines, thereby saving both time and resources.

Based on the cultivation pattern of the producer in the nutrient medium, surface and submerged fermentations are distinguished. It must be emphasized that the majority of biological objects used as producers of biotechnological products are aerobes.

In surface fermentation, the biological object grows exclusively On the surface of a liquid nutrient medium. Although the target product (if Water-soluble) disperses throughout the entire volume of the medium, the biomass of its producer is located solely as a surface film in containers of any kind: flasks (including so-called microbiological Roux bottles), bottles, and finally, even in a fermenter, provided that the stirrer and sparging device are turned off—meaning there is neither mass transfer nor aeration. The resulting biomass is very small, and consequently, so is the target product yield.

In submerged fermentation, despite differences in fermenter designs, the producer Cells are driven throughout the entire volume of the nutrient medium by the action of an agitator or turbine mixing and the forced passage of air under pressure through the entire bulk of the medium. This makes the process highly economical. The fermenter creates conditions for the accumulation of a large amount of actively functioning producer biomass and, accordingly, the target product.

As an example from the History of Biotechnology, it can be noted that replacing surface fermentation (in flasks and bottles) with submerged fermentation (in fermentation apparatuses) made it possible to rapidly and dramatically increase The production of penicillin, which was acutely needed during World War II.

Finally, fermentation processes can also be technologically differentiated by the type of target product. The target product may be biomass; an individual high-molecular-weight substance (typically an enzyme, either constitutive or inducible); or a low-molecular-weight metabolite. The metabolite, in turn, can be primary or secondary. Thus, The Need for Inducers and precursors, as well as the timing of their Introduction into the medium, depends on the target product. Since The biosynthesis of secondary metabolites is characteristic of specific Developmental Stages of the producer culture and is stimulated under so-called stress conditions—such as the depletion of carbon, nitrogen, and phosphorus sources in the medium—the addition of inducers and precursors is mandatory when the primary objective of the fermentation process is a secondary metabolite.

The biomass accumulation curve generally coincides with the curve of primary metabolite accumulation and does not coincide with the accumulation curve of secondary metabolites. In particular, this applies to secondary metabolites such as Antibiotics, which accumulate most rapidly in the medium precisely when biomass growth has nearly plateaued.

During the Isolation and Purification of the target product, significant differences between biotechnological and chemical-technological manufacturing emerge only at the initial stage of operations. This is due to the specific feature of the biotechnological process—the necessity of separating the target product from the biomass (commonly referred to as "mycelium").

If the target product is water-soluble, it ends up in the culture liquid upon draining. The mycelium can be separated by filtration using various techniques (filter presses, etc.) or by centrifugation.

If the target product accumulates within the mycelium, the Solid and liquid phases are separated, after which the target product is extracted from the mycelium. To improve mycelial recovery from the culture liquid (when the target product is contained therein), preliminary coagulation is sometimes employed to facilitate the Separation of the mycelium.

Review Questions

1. What does the preliminary preparation of the fermentation process entail?

2. What is the main process, and which biosynthesis parameters are considered controllable?

3. What is meant by "fermenter piping and peripherals," and what is its significance?

4. How can active mass transfer be ensured in a fermenter, taking into account the Specifics of the cultivated biological objects?

5. What is the difference between submerged and surface fermentation? Which biological objects are used in each specific case?

6. What factors (physical, chemical, and biological) influence the fermentation process?

7. Describe The process of propagating seed material. What stages does it consist of?

8. How is sterility maintained throughout the biotechnological production process?

9. What criteria can be used to characterize the biosynthesis process?

10. WHAT IS A culture passport?