Week 4 Lecture Kinetics and Monitoring Growth Flashcards
What is Kinetics of growth
Orderly increase in cellular components, resulting in cell enlargement and eventually leading to cell division
-Ideally growth kinetics is a homogeneous unicellular suspension culture
-We can use differential equations in continuum model
-Divisions produce identical daughter cells
-Generation vs. generation time
Why do we need good mixing in bioreactor for kinetics of growth?
-Biomass and number of cells will increase
-We need good mixing in bioreactor because we want to have an even heat transfer, even concentration of substrate, want it to be homogenous
-If there is no synchronous growth everything will be upside down, certain microbes in stationary phase and growth phase when they’re not supposed to be
-In stationary phase strictly control concentration of substrates so we don’t go to exponential phase too soon
What are the issues of Kinetics?
-Increase of biomass vs. increased number of cells due to division
-Asynchronous growth vs. synchronous
-Fermentation under different operating conditions (batch, fed-batch, continuous)
What happens if there is no synchronous growth?
-If there is no synchronized growth and homogenous conditions, microbes will all be in different phases, no correlation between biomass growth and increasing number of cells in bioreactor
-Growth rate in stationary phase slower than growth rate in exponential phase
What are the different growth phases?
-Lag
-Acceleration
-Exponential
-Deceleration
-Stationary
-Death phase
What is Lag phase?
-Intense metabolic activity
-Length of lag time depends on the age, -phase of growth microorganisms were taken from
-Chemical composition of fermentation media influences the length of lag time
-Physiological stress (inoculum moved from low osmotic to high osmotic pressure)
What is acceleration phase?
Cell division with increased rate until max growth rate umax is reached
What is the exponential phase?
-Growth begins cell number/biomass increase at a constant rate (x biomass, N number of cells)
-When a cell divides we say generation and time it takes is called mean generation time
-Mean generation time (doubling the number) td=t/n
-Division rate constant n/t
–Once substrates are consumed growth rate of microbes is going into deceleration phase
What is exponential growth?
Exponential growth begins when all nutrients are supplied in excess, then there is a relationship between # of cells and biomass then we have balanced growth
What is the Deceleration phase?
-Level of substrate decreases, becoming limiting and can not sustain max growth rate
-Limiting substrate is metabolized then growth is no longer sustainable
What is the Stationary phase?
-No net change in cell number; rate of divisions=rate of death of cells; but microorganisms are still metabolically active using intracellular storage compounds
What is Death phase?
-Cells die or can form spores to survive depending
What is Batch fermentation?
-Not steady state because: rate constant (u) changes, substrate concentration decreases, product-biomass concentration increases, pH changes, temperature might change (if we do not control the heat), and there is an accumulation of byproducts
-operations involve; charging water and substrates, sterilization, inoculation, production of products, harvesting, cleaning
Fed-batch (continuous process)?
-CSTR experiment is an example
What is the Kinetics growth equation?
xt=x0 * e^ut or ln xt= u*t + lnx0
x= grams of biomass
t=time
u= rate constant
