lecture notes-growth kinetics--growth phases.ppt

7/23/2019 lecture notes-growth kinetics--growth phases.ppt

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Cell Growth Kinetics

- Introduction

- Growth patterns and kinetics in batchculture

- growth phases

- effect of factors: oxygen supply

- heat generation

- Growth kinetics (Monod Euation!

- Growth in continuous culture (idealche"ostat!


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Growth Kinetics

Introduction- #utocatalytic reaction: $he rate of growth is directly related to

cell concentration

substrates % cells & extracellular products % "ore cells

' % ) & '* % n)

: substrate concentration (g+,! ): cell "ass concentration (g+,!

*: product concentration (g+,! n: increased nu"ber of bio"ass./et specific growth rate (0+ti"e!:

t: the ti"e dt

dX

X

1net


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Growth Kinetics

Introduction/et specific growth rate (0+ti"e!:

d

k

g

=

net:g Gross specific growth rate (0+ti"e!

:dk $he rate of loss of cell "ass due to cell death

or endogenous "etabolis"

Endogenous "etabolis": during the stationary phase1

the cell cataboli2es cellular reser3es for new building blocks and

for energy-producing "ono"ers.


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Growth Kinetics

Introduction/et specific replication rate (0+ti"e!:

dt

dN

N

1

R

:'R

Gross specific replication rate (0+ti"e!

:

dk

$he rate of cell death (0+ti"e!

R

dk= 'RR

/ : Cell nu"ber concentration (cell nu"ber +,!


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Growth Kinetics

Introduction- 4uantifying cell concentration:

- direct: no suspended solid and interference

co"pounds.

cell "ass concentration 5 preferred

dry weight1 optical density (turbidity! (677-877n"

9a3e ,ength!cell nu"ber density:

*etroff-ausser slide (he"ocyto"eter!1 plate counts1

etc.


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Growth Kinetics

- 4uantifying cell concentration:

- indirect: direct "ethod is inapplicable. ("old solid

state fer"entation!

Cell "ass can be deter"ined by "easure"ent

of protein1 ;/# or #$*. e.g. 0"g #$*+g dry weight

bacterial cell.

If 077 "g #$*+, is "easured1 then the cell "ass:

077 "g (#$*+,!+0 "g #$*+g dry cells


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Growth Kinetics

- Growth patterns and kinetics in batch culture

- growth phases

In batch culture:

- lag phase

- logrith"ic or exponential growth phase

- deceleration phase

- stationary phase

- death phase


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$ypical growth cur3e for a bacterial population


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Lag phase

# period of adaptation for the cells to their

new en3iron"ent

= /ew en2y"es are synthesi2ed.

= # slight increase in cell "ass and 3olu"e1 but no

increase in cell nu"ber

= *rolonged by low inoculu" 3olu"e1 poor

inoculu" condition (high > of dead cells!1 age of

inoculu"1 nutrient-poor "ediu"

=Multiple lag phases: (diauxic growth! "ediu"

contains "ore than one carbon source

?atch Growth Kinetics


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;iauxic growth


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Exponential growth phase

In this phase1 the cells ha3e ad@usted to

their new en3iron"ent and "ultiplyrapidly (exponentially!

= ?alanced growth 5all co"ponents of a cell

grow at the sa"e rate.= Growth rate is independent of nutrient

concentration1 as nutrients are in excess.


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0tandtat timeionsconcentratcellare0XandX

0or,0

ln

:yieldsequationabovetheofnIntegratio

00,

=

==

===

teXXtnet

X

X

tatXXXnetdt

dX

net



$he balance of cell "ass in a batch culture

gi3es:


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constant.isslopehe net


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!1"time#rategro$thspecificma%imumtheis

R

m

mnet ==



;oubling ti"e of cell "ass: the ti"e reuired to double

the "icrobial "ass:

netnetnet

&(.0)ln0"ln

===

XXd


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Deceleration growth phase

Aery short phase1 during which growth decelerates

due to either:= ;epletion of one or "ore essential nutrients

= $he accu"ulation of toxic by-products of growth

(e.g. Ethanol in yeast fer"entations!= *eriod of unbalanced growth: Cells undergo

internal restructuring to increase their chances ofsur3i3al


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Stationary Phase:9ith the exhaustion of nutrients (B7! and build-up

of waste and secondary "etabolic products

- $he growth rate euals the death rate.- $here is no net growth in the organis" population.

- Cells "ay ha3e acti3e "etabolis" to produce secondary"etabolites.

*ri"ary "etabolites are growth-related: ethanol by S.cerevisae.

econdary "etabolites are non-growth-related:antibiotics1 pig"ents.


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Kinetic *attern of Growth and

*roduct or"ation

Growth-associated /on growth-associatedMixed-growth-associated


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?atch Growth KineticsStationary phase

- Cell lysis "ay occur and 3iable cell "ass "ay drop.

# second growth phase "ay occur and cells "ay grow onlysis products of lysed cells (cryptic growth!

- Endogenous "etabolis" occurs by cataboli2ing cellularreser3es for new building blocks and energy-producing"ono"er ("aintenance energy!.

$he rate describing the con3ersion of cell "ass into

"aintenance energy or the loss of cell "ass due to celllysis:

.metabolismendogenousforconstantratetheisd

d

k

Xkdt

dX=


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Death Phase:$he li3ing organis" population decreases with ti"e1

due to a lack of nutrients and toxic "etabolic by-

products.

$he rate of death usually follows:

constant.ratedeathorder*firsttheis'

'

d

d

k

Nkdt

dN=


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Dield coefficients: defined based on the a"ount of

consu"ption of another "aterial.

)

:o%ygenofnconsumptioonbasedyield+ro$th

:yield,roduct

:yield+ro$th

)"

"

"

O

X

Y

SPY

S

XY

OX

SP

SX

energyemaintenancenergygro$th

product

lare%tracelluaninto

onassimilatibiomassinto

onassimilati SSSSS +++=


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Dield coefficients: defined based on the a"ount of

consu"ption of another "aterial.

or "ost bacteria and yeast:

Dx+s

lecture notes-growth kinetics--growth phases.ppt

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