Lec 2 - Continuous Culture

Question 1

Why is it beneficial if fresh medium is added to the culture continuously/periodically?

Answer 1

• culture always receives fresh nutrients - dilution of autoinhibitory products

Question 2

What are the 2 types of apparatus used for continuous cultures.

Answer 2

Turbidostat Chemostat

Question 3

Draw diagrams of both a turbidostat and chemostat

Answer 3

Question 4

Describe the basic mode of operation of a turbidostat & chemostat

Answer 4

Turbidostat - spectrophotometer measures OD of culture. if OD / population becomes too high then Pump1 pumps in fresh medium. bacteria grow @ max growth rate Chemostat - fresh medium continuously pumped in. limiting nutrient exists in the culture - growth rate depends on this limiting nutrient. eventually growth rate = dilution rate. works to uncouple population density from growth rate

Question 5

Which 4 parameters are controlled in both a chemo/turbidostat and which parameter is additionally controlled in chemostats

Answer 5

chemo/turbidostat - pH, aeration & agitation, culture volume, anti foam chemicals chemostat - flow rate

Question 6

What is one problem that can occur when using turbidostats?

Answer 6

build up of organisms on sides of apparatus - including over the spectrophotometer -> false readings

Question 7

Give the 5 basic chemostat equations

Answer 7

D (h) = F (flow rate/ml h) / V (ml) Change in biomass (dx/dt) = x(u - D) (growth - washout) change in limiting sub. concn (ds/dt) = DSr - Ds - qx (sub conc in influent - effluent - growth rate of uptake of sub) rate of uptake of limiting nutrient (q) = u / Y (yield - grams of bacteria/mole substrate consumed) u = umax (s / Ks + s)

Question 8

What is Ks?

Answer 8

The subs conc @ half max growth rate. low Ks = bacteria good @ scavenging for nutrients

Question 9

Chemostats are used to examine the _____ of an organism at a range of _____ rates that are _____ of cell density

Answer 9

metabolism growth independent

Question 10

How would we measure the growth parameters using a chemostat?

Answer 10

• Decide on an Sr that would give suitable cell density. do not set D too high - allow for initial growth of cells - allow the system to reach a steady state (5 full washes of medium) - measure s, q, x - already know Sr and D - increase the D - new steady state & retake measurements - until we reach Dc

Question 11

What is the Dc?

Answer 11

critical dilution rate Dc = umax (cells cant grow any quicker) once Dc exceeds umax then the culture washes out