Lecture 6+11 (media comp. + control of BRs)

Question 1

Which different organisms are there in the category energy source?

Answer 1

Chemothrophs (lithotrophs and organotrophs)

and phototrophs

Question 2

Which different organisms are there in the category carbon source?

Answer 2

heterotroph (org. compound) and autotroph (CO2)

Question 3

What does the media selection affect?

Answer 3

pH variation, Foam formation, Redox potential, Morphology, Product recovery (cleaning before pure product) and Effluent treatment (waste wate)

Question 4

What defines a complex media?

Answer 4

nutrients in complex form - not well defined. batch variations, can be hard to sterilize, complicates product recovery. low price, high yield

Question 5

What defines a defined media?

Answer 5

defined nutrients, well-defined process, less problem in sterilization, clear solution, simple down stream process. media design is hard, expensive. Most often used when producing pharmaceutical proteins!

Question 6

Give some examples of nitrogen sources

Answer 6

Inorganic - ammonia gas, nitrates

Organic - amino acids, urea complex (soy bean hydrolysate, corn step liquor etc.)

Question 7

What can chelators be good for?

Answer 7

To avoid precipitation of salts/minerals

Question 8

What causes foaming?

Answer 8

caused by proteins or microbial activity. Can result in wash-out of cells, autolysis change mass balances etc.

Question 9

Why limit sugar uptake?

Answer 9

to avoid catabolite repression and overflow metabolism

Question 10

Whats the reason for overflow metabolism?

Answer 10

High glucose uptake rate, Limited respiratory capacity, Repression of respiratory genes (TCA, ETC) due to catabolite repression.
Enzyme kinetics favour fermentative pathways over TCA cycle at increased
pyruvate concentration
Typical products: Ethanol, acetate, other alcohols and organic acids

Question 11

How can overflow metabolism be avoided?

Answer 11

• Limit substrate
• continuous, fed-batch or perfusion culture
• measure the controlled variables
• adjust feed rate
• Use controller

Question 12

Where should the controller sit to control overflow metabolism in the culture?

Answer 12

It should be connected to the analyzer/detector after the sampling - and then connected to the pump to control the fed rate

Question 13

What is a PID contoller?

Answer 13

A PID controller calculates controller output u due to error e between
set point Ysp and actual value y at time t, to reduce the error e

Question 14

What does the PID give you? And what is it based on..

Answer 14

New feed rate (u(k)) = Old feed rate (u(k-1)) + Proportional change (Kp) + Integrative change (Ki) + derivative change (Kd).
The constants Kp-d are set by yourself

Question 15

Which metabolic pathway is favored when high vs. low glucose for S. cerevisae?

Answer 15

high: TCA cycle
low: ethanol and acetate production

Question 16

What is the critical dilution point? /crabtree effect

Answer 16

when the respiratory process in not enough to metabolize the excess glucose. - Start prod. ethanol. The point can be hard to know so u need a good resolution for measuring small ethanol conc.
Measure and calculate the RQ!

Question 17

What happens when E.Coli is grown aerobically at high glucose?

Answer 17

Produces acetate! Respiratory genes are repressed, competition of pyruvate. Increased acetate due to increased ATP requirement for plasmid and protein prod.