22.7 culturing microorganisms industrially

what are the advantages of using a continuous culture (4)

• Steady-State Growth: Continuous cultures maintain a constant exponential growth rate, ideal for the production of products such as antibiotics, enzymes, and biomass.

• Higher Yield: Since microorganisms are always in the exponential phase, a continuous culture can produce a larger quantity of biomass or product over time compared to batch cultures.

• Resource Efficiency: Nutrients and oxygen are added as needed, and waste is removed, leading to optimal growth conditions for microorganisms.

• Control over Environment: The conditions can be carefully controlled (e.g., temperature, pH, oxygen levels) to maintain optimal growth conditions, enhancing productivity and consistency for production of primary or secondary metabolites

what are the disadvantages of continuous cultures? (3)

• Complexity: Continuous cultures require sophisticated equipment (e.g., bioreactors) and constant monitoring of the system (e.g., nutrient levels, pH, temperature), making it more complex and expensive than batch cultures.

• Contamination Risk: Continuous systems can be more vulnerable to contamination by unwanted microorganisms, which can disrupt the culture and potentially ruin the product.

• Limited Product Formation: Some products may be more efficiently produced in batch cultures, especially those that require high cell density or specific conditions that are difficult to maintain continuously.

what is a continuous culture? (2)

In a continuous culture, microorganisms (e.g., bacteria, yeast) are cultured under conditions where nutrients are constantly provided, and waste products are removed at the same rate. This keeps the microorganisms in the log phase (exponential growth phase) for a prolonged period, resulting in a continuous, stable growth rate.

why is a mixing mechanism often found in bioreactors?

large volumes of liquid are in bioreactors and often that liquid is quite viscous due to the microorganisms growing, so oxygen and other nutrients are evenly distributed in the culutre

maintain constant temps, as some areas may otherwise be a lot cooler/hotter.

What are primary metabolites

Substances produced as an essential part of the normal functioning of a microorganism

When are primary metabolites usually formed^D

During the active growth phase

Examples of primary metabolites (3)

-Amino acids
-ethanol
-enzymes

What are secondary metabolites

Substances produced which are not essential for normal growth, but are still used by the cells (e.g. as a result of increased competition)

When are secondary metabolites usually formed

During the stationary phase, once the cell mass has reached its maximum

Examples of secondary metabolites

Penicillin antibiotics

What are the 2 different types of fermentation in bioprocessing

-Batch fermentation
-continuous culture

Outline the process of batch fermentation (4)

1. Microorganisms inoculated into a fixed volume of medium
2. As growth takes place, nutrients are used up and both new biomass and waste products build up
3. As the culture reaches the stationary phase, overall growth ceases, but during this phase, the microorganisms often carry out biochemical changes to form the desired products (e.g. antibiotics)
4. The process is stopped before the death phase, and the products harvested. The whole system is cleaned and then a new batch culture is started up

Outline continuous fermentation

1. Microorganisms are inoculated into sterile nutrient medium and start to grow
2. Sterile nutrient medium is added continually to the culture once it reaches the exponential point of growth
3. Culture broth is continually removed, the medium, waste products, microorganisms and product- keeping the culture volume in the bioreactor constant

Advantages of batch production (2)

-Easy to set up
-less of an impact if contaminated

Disadvantages of batch production (2)

-Slower growth rate as nutrient levels decrease with time
-less efficient as fermenter is not operating 24/7

why is it important to have aseptic conditons (4)

to avoid unwanted microbe

, entry / presence ; so no competition for nutrients ; so conditions remain unchanged ;

so no decrease in yield ; so no contamination of , batch / product / penicillin or batch is unusable

; to prevent escape of , microbes / fungus / Penicillium / spores

why secondary metabolites not produced initially? (3)

they are not essential to growth

-most secondary metabolites like pencillin require other more complex biological molecules and more atp to create, so the organism has to focus on establishing its primary metabolites first

idea that most penicillin produced after main growth phase ; after 24 h / when nutrients declining ; not needed for growth ;

why is a cooling system usually needed?

bacteria are always in there exponent phase, so there is large number of bacteria

heat is released through exothermic metabolic reactions e.g. respiration

increase in temp, could denature enzymes

how can you tell if a reactor is continuous?

Has an outlet for products, reactants and waste products so the process doesnt have to be stopped, as they are funneled into the reactor

why is ammonia and oxygen added to bioreactors?

bacteria may oxidise ammonia into nitrates, so they can absorb it easily to make amino acids and nucleic acids.