Microbial Growth

Question 1

Methods for Measurement of Cell Mass? 1

Answer 1

Direct physical measurement of dry weight, wet weight, or volume of cells after centrifugation

Question 2

Methods for Measurement of Cell Mass? 2

Answer 2

Direct chemical measurement of some chemical component of the cells such as total N, total protein, or total DNA content

Question 3

Methods for Measurement of Cell Mass? 3

Answer 3

Indirect measurement of chemical activity such as rate of O2 production or consumption, CO2 production or consumption

Question 4

Methods for Measurement of Cell Mass? 4

Answer 4

Turbidity measurements employ a variety of instruments to determine the amount of light scattered by a suspension of cells

Question 5

Methods for Measurement of Cell Numbers? 1

Answer 5

Direct microscopic counts - using special slides known as counting chambers. Dead cells cannot be distinguished from living ones. Only dense suspensions can be counted

Question 6

Methods for Measurement of Cell Numbers? 2

Answer 6

Electronic counting chambers count numbers and measure size distribution of cells

Question 7

Methods for Measurement of Cell Numbers? 3

Answer 7

plating out (spreading) a sample of a culture on a nutrient agar surface. If plated on a suitable medium, each viable unit grows and forms a colony

Question 8

Advantages and disadvantages of 3

Answer 8

+ve:Sensitivity, and it allows for inspection and positive identification of the organism counted.
-ve: Only living cells develop colonies that are counted
Clumps or chains of cells develop into a single colony

Question 9

What are the four phases in microbial growth?

Answer 9

Lag, exponential, stationary and death

Question 10

What happens in each stage

Answer 10

microbes are adjusting to the new substrate (food source), synthesising enymes/rna and increasing m.a

microbes have acclimated to the conditions and cells divide at a constant rate by binary fission

limiting substrate or electron acceptor limits the growth rate: exhaustion of nutrients, accumulation of inhibitory metabolites, exhaustion of space

substrate supply has been exhausted

Question 11

Final population equation?

Answer 11

X=X0.2^N
lnX=lnX0+nln2
n=t/td
No of generations= total time/doubling time

Question 12

Growth rate equation

Answer 12

ln x = ln x0 + µt

X=X0.exp(µt)

Question 13

SPECIFIC GROWTH RATE µ

equation

Answer 13

µ = µmax . s/(Ks + s)

µmax is maximum specific growth rate which
occurs when s is large
Ks is substrate saturation constant
(µ to s at µmax/2).

Question 14

To calculate µmax and Ks

from Monod growth kinetics

Answer 14

Plot 1/µ vs 1/S (as in enzyme kinetics) –> straight line
y axis intercept –> 1/µmax
x axis intercept –> -1/Ks
Also slope = Ks/µmax so if µmax is known Ks can be calculated.

Question 15

What is continuous culture?

Answer 15

a system that is designed for long-term operation. Continuous culture = open system

Question 16

What does the feed contain?

Answer 16

nutrients and substrate, as well as a continuous drain of effluent solution that contains cells, metabolites, waste products, and any unused nutrients and substrate

Question 17

What is a chemostat

Answer 17

allows control of the rate of growth, which can be used to optimize the production of specific microbial products

Question 18

What parameters can be controlled

Answer 18

Dilution rate and influent substrate concentration

Question 19

What do these parameters do?

Answer 19

By controlling the dilution rate, can control the growth rate (µ) represented in this graph as doubling time
By controlling the influent substrate concentration, control the number of cells produced or the cell yield in the chemostat

Question 20

Problem of chemostats?

Answer 20

difficult to maintain sterile conditions over time.

Question 21

What is the equation for the change in biomass with time?

Answer 21

dX/dt=µX-DX

X is the cell mass (mass/volume), µ = specific growth rate (1/time), and D is the dilution rate (1/time).

Question 22

If µ is more than D?

Answer 22

Utilization of substrate will exceed the supply of substrate, causing the growth rate to slow until it is equal to the dilution rate

Question 23

if µ is less than D?

Answer 23

the amount of substrate added will exceed the amount utilized. Therefore the growth rate will increase until it is equal to the dilution rate

Question 24

Relationship of D and Dc?

Answer 24

dilution rates less than Dc , operation efficiency is not optimized, whereas if dilution rates exceed Dc , washout of cells will occur

Question 25

Equation of cell yield?

Answer 25

Cell yield coefficient is defined as the amount of cell mass produced per amount of substrate consumed.

Question 26

Applications of this?

Answer 26

• Wastewater treatment
• Production of high value microbial products (e.g., antibiotics , vitamins, therapeutic proteins)
• Remediation of contaminated sites.