Microbial Growth Flashcards
Methods for Measurement of Cell Mass? 1
Direct physical measurement of dry weight, wet weight, or volume of cells after centrifugation
Methods for Measurement of Cell Mass? 2
Direct chemical measurement of some chemical component of the cells such as total N, total protein, or total DNA content
Methods for Measurement of Cell Mass? 3
Indirect measurement of chemical activity such as rate of O2 production or consumption, CO2 production or consumption
Methods for Measurement of Cell Mass? 4
Turbidity measurements employ a variety of instruments to determine the amount of light scattered by a suspension of cells
Methods for Measurement of Cell Numbers? 1
Direct microscopic counts - using special slides known as counting chambers. Dead cells cannot be distinguished from living ones. Only dense suspensions can be counted
Methods for Measurement of Cell Numbers? 2
Electronic counting chambers count numbers and measure size distribution of cells
Methods for Measurement of Cell Numbers? 3
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
Advantages and disadvantages of 3
+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
What are the four phases in microbial growth?
Lag, exponential, stationary and death
What happens in each stage
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
Final population equation?
X=X0.2^N
lnX=lnX0+nln2
n=t/td
No of generations= total time/doubling time
Growth rate equation
ln x = ln x0 + µt
X=X0.exp(µt)
SPECIFIC GROWTH RATE µ
equation
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).
To calculate µmax and Ks
from Monod growth kinetics
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.
What is continuous culture?
a system that is designed for long-term operation. Continuous culture = open system
What does the feed contain?
nutrients and substrate, as well as a continuous drain of effluent solution that contains cells, metabolites, waste products, and any unused nutrients and substrate
What is a chemostat
allows control of the rate of growth, which can be used to optimize the production of specific microbial products
What parameters can be controlled
Dilution rate and influent substrate concentration
What do these parameters do?
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
Problem of chemostats?
difficult to maintain sterile conditions over time.
What is the equation for the change in biomass with time?
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).
If µ is more than D?
Utilization of substrate will exceed the supply of substrate, causing the growth rate to slow until it is equal to the dilution rate
if µ is less than D?
the amount of substrate added will exceed the amount utilized. Therefore the growth rate will increase until it is equal to the dilution rate
Relationship of D and Dc?
dilution rates less than Dc , operation efficiency is not optimized, whereas if dilution rates exceed Dc , washout of cells will occur
Equation of cell yield?
Cell yield coefficient is defined as the amount of cell mass produced per amount of substrate consumed.
Applications of this?
- Wastewater treatment
- Production of high value microbial products (e.g., antibiotics , vitamins, therapeutic proteins)
- Remediation of contaminated sites.
