22.6 culturing microorganisms in the lab

what is the lag phase?

the lag phase is when the bacteria are adapting to their environment, they are growing and synthesising the enzymes needed

what is the exponential phase?

it is when the rate of bacterial reproduction is close to its theoretical maximum

what is the stationary phase?

occurs when the total growth rate of bacteria is zero, as the number of new cells forming is canceled out by the number of cells dying

what is the decline or death stage?

`comes when reproduction has almost ceased, and the rate of cell death is increasing

what are the limiting factors and explain why it prevents growth?

1. nutrients available- nutrient level becomes insufficient, so they won’t be able to carry out metabolic reactions that are essential for life

2. oxygen levels- as the population rises, more oxygen is used up

3. temperature- enzyme-controlled reactions within microorganisms are affected by the temp of the culture medium. For most bacteria, a low temp slows down growth and reproduction. if temps too high, enzymes denature

4. waste products like ethanol and lactic acid, ammonia

5. -changing in pH

why is it important to culture microorganisms in aseptic conditions?

there is a risk that a mutation taking place making a strain pathogenic

there may be contamination with pathogenic microorganisms from the environment

what is the food provided to the microorganisms called?

nutrient medium

why do we need to provide nutrients to some microorganisms? (2)

some microorganisms need a precise balance of nutrients

this allows for microorganisms to reproduce rapidly

how do you make an inoculating broth (4)

1. make a suspension of the bacteria to be grown

2. mix a known volume of sterile broth to the flask

3. stopper the flask with cotton wool to prevent contamination

4. incubate at a suitable temp, shaking regularly to aerate the broth providing oxygen and allowing for waste products to be removed

how do you make an inoculating broth? (5)

1. wire inoculating loop is first sterilized by holding it near a Bunsen burner flame

2. allow it to cool but do not let it touch any other surface

3. dip sterilized loop in the bacterial suspension

4. remove lid of petri dish and make a zig-zag streak across the surface of the agar. Do not dig into the agar

5. replace lid of Petri dish and seal it with tape, however, make sure it is not sealed completely so oxygen can get in which prevents the growth of anaerobic bacteria