Lecture 1: Microbial Biotechnology, Microbial Growth, and Fermenter Techniques

Question 1

What are the requirements for a microbe to be used in biotechnological production

Answer 1

1. Organism: easily fermented, robust, stable, safe
2. Process: needed (supply & demand), ethical

Question 2

What are some common biotech organisms?

Answer 2

1. Escherichia Coli: Gram -, genetically traceable, used for recombinant protein production (e.g., insulin), cells require liaison
2. Bacillus subtilis: Gram +, genetically traceable, used for production of amylases, proteases etc, no lysis required
3. Aspergillus niger: Eukaryote, Filamentous fungi, used for prod of citric & glucuronic acid, Lignocellulosic degrading enzymes secreted so can be grown on solid media (e.g., straw)

4 Yeast: simplest eukaryote, prod of ethanol, biomass, and bread

5. Streptomyces: numerous antibiotic & antifungal compounds, used for prod and discovery of antibiotics

Question 3

What are the important ‘parameters’ (pieces of the ‘equation’) are there?

Answer 3

GROWTH RATE (u): change in biomass over time
SUBSTRATE RATE (rs): decrease in substrate over time
PRODUCT RATE (rp): increase in product over time

YIELD OF BIOMASS:
Ysx = u/rs units: g mol-1
YIELD OF PRODUCT:
Ysp = rp/rs units: mol mol-1

PRODUCTIVITY QUOTIENT qp = yield/time
units eg: mol mol-1hr-1

Question 4

How can we measure cell growth via cell mass?

Answer 4

1. Physical measurement: of dry weight, wet weight, or volume of cells after centrifuging
2. Chemical measurement: of some chemical component of the cells such as total N, protein, or DNA
3. Chemical activity: O2 prod or CO2 consumption
4. Turbidity measurements: ‘optical density’ of a suspension is directly related to cell number/mass

Question 5

How can we measure cell growth via cell number?

Answer 5

1. Direct microscopic counts: using counting chambers (only dense suspensions can be counted - 10^7 cells ml-1)
2. Electronic counting chambers: count no. and measure size distribution
3. Indirect viable cell counts: ‘plate counts’, counting the no of CFU’s
4. Turbidity measurements

Question 5

How can we measure cell growth via cell number?

Answer 5

1. Direct microscopic counts: using counting chambers (only dense suspensions can be counted - 10^7 cells ml-1)
2. Electronic counting chambers: count no. and measure size distribution
3. Indirect viable cell counts: ‘plate counts’, counting the no of CFU’s
4. Turbidity measurements

Question 6

What limits bacterial growth?

Answer 6

1. Nutrient availability/accessibility
2. Waste build-up
3. Quorum sensing

Question 7

What is the specific growth rate/relative growth rate?

Answer 7

U. The exponential growth phase.

It is a measure of change in biomass/cell count RELATIVE to the starting cell concentration/biomass

Question 8

What affects the growth yield?

Answer 8

1. Nature of C source
2. Pathways of substrate catabolism
3. E req. for assimilation of other nutrients
4. Physiological state and efficiency of the organism