Let 4 - Continuous Culture (pros/cons)

Question 1

Give the 5 advantages of using a continuous culture to determine growth rate parameters.

Answer 1

• can work out umax, Ks, qm and Yd
• growth rate is maintained and controlled indefinitely
• biomass is kept constant whilst D changes (can be useful for studying components eg RNAseq that require the same physiological conditions)
• used to apply selection pressure to select for a mutant under specific conditions
• growth limiting nutrient can be altered and effects of this on metabolic activity/cellular components can be observed

Question 2

Give the 2 disadvantages of continuous cultures

Answer 2

• aggregation of cells on wall/biofilm production can disrupt steady state growth & lead to increased biomass
• growth of mutants can overtake growth of original bacteria in culture

Question 3

What are enrichment cultures used for and give an example.

Answer 3

used to isolate/identify any bacteria that have specific attributes
eg identifying bacteria that have the ability to degrade toxic tetrachloroethene source

Question 4

Why do we need to isolate bacteria that can degrade tetrachloroethene ?

Answer 4

when tetra leaches into the soil it is toxic to the environment

Question 5

How do we identify and isolate bacteria that can break down tetrachloroethene using a chemostat?

Answer 5

• have a fully defined medium w/ the toxic compound (tetra) being the only C source
• any growth we see will be as a result of bacteria utilising this source
• in microcosm the culture @ the end will be able to breakdown and utilise tetra (however this batch culture method is v slow)
• in chemostat we pump in toxic C source @ low rates to allow initial growth
• when growth is seen we increase D to select for bacteria that are the quickest @ breaking down the polluted soil/water

Question 6

What are the problems that can arise with this method?

Answer 6

• partial degradation of the compound leading to a more toxic compound eg tetra partial degradation gives a chloride compound = v toxic
• no degradation at all - if this is the case add a 2nd C source that can be degraded which will hopefully kickstart the growth of mutants. mutants that can utilise both C sources will have a selective advantage over others