Culturing microorganisms

Question 1

What are the two forms of nutrient medium that provide food for bacteria?

Answer 1

broth (liquid form) and agar (solid form)

Question 2

What is inoculation?

Answer 2

the process of adding bacteria to a growth medium

Question 3

How is bacteria added to a broth?

Answer 3

1. make a suspension of the bacteria to be grown
2. mix a know volume with the sterile nutrient broth in the flask
3. stopper the flask with cotton wool to prevent contamination from air
4. incubate at suitable temperature, shaking regularly to aerate the broth providing O2 for bacteria

Question 4

How is bacteria added to agar?

Answer 4

1.wire inoculating loop must be sterilised in bunsen flame
2. dip sterilised loop in bacterial suspension
3. rub loop on agar, avoid digging into agar and spread evenly across the surface
4. hold lid down with tape not cutting off oxygen
5. incubate at suitable temperature

Question 5

What are the 4 phases of bacterial growth and what happens in each one?

Answer 5

lag phase - bacteria adapt to new environment
log phase - rate of reproduction is at theoretical maximum
stationary phase - growth rate is zero
death phase - reproduction has almost ceased and death rate of cells is increasing

Question 6

What are the several limiting factors preventing exponential growth of bacteria?

Answer 6

available nutrients, oxygen levels, temperature, build up of waste and pH change

Question 7

What is a primary metabolite?

Answer 7

substances that are produced which are essential for growth and reproduction

Question 8

What is a secondary metabolite?

Answer 8

substances produced that are not essential for growth or reproduction

Question 9

What are the two main ways of growing microorganisms?

Answer 9

Batch fermentation and continuous culture

Question 10

Explain how batch fermentation works?

Answer 10

microorganisms are inoculated into a fixed volume of nutrient medium and as growth takes place, nutrients are used up and new product and waste build up. As culture reaches stationary phase growth ceases and end product is formed. Process is stopped before death phase and product is harvested and whole system is cleaned and sterilised

Question 11

How does continuous culture work?

Answer 11

microorganisms are inoculated into sterile nutrient medium and start to grow. Nutrient medium is continuously added once log phase is reached. products, waste and medium is continually removed keeping a constant volume in the bioreactor

Question 12

What needs to be controlled in a bioreactor?

Answer 12

temperature, pH, nutrients, oxygen and asepsis