Lecture 2

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22 Φεβ 2013 (πριν από 4 χρόνια και 7 μήνες)

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Microbial Growth Kinetics

Lecture 2


Tahir


Fermenters

Fermentation Process

Fermentation Technology

-
> Fermentation: from latin
-
> ”
fervere

-
> to boil (describing the
anaerobic process of yeast
producing CO
2

on fruit extracts)


-
> Nowadays: more broad meaning!!!!


The five major groups of commercially important fermentations:


-
> Process that produces
microbial cells (Biomass)
as a product

-
> Process that produces
microbial enzymes
as a product

-
> Process that produces
microbial metabolites (primary or secondary)
as a product

-
> Process that produces
recombinant products (enzymes or metabolite)
as a product

-
> Process that
modifies a compound that is added to the fermentation


transformation process

Growth: basic concepts

Anabolism

= biosynthesis

Catabolism

= reactions to
recover energy (often ATP)

Precursors

Regeneration of NAD
+

Fermentation

Respiration

No added terminal e
-
-
acceptor

Oxidant = terminal e
-
-
acceptor

ATP: substrate level phosphorylation

ATP: (e
-
-
transport) oxidative phosphoryl.

Glucose

2 Glyceraldehyde
-
3
-
P


2 ATP


2 NADH

2 Pyruvate

2
Lactate

+ 2
H
+

Acetaldehyde

+2
CO
2

2
Ethanol

Acetate

+ Formate

H
2

+
CO
2

Glucose


2 ATP


2 NADH

2 Pyruvate

2 Acetyl
-
CoA

CO
2

Citric acid

cycle


CO
2


GTP


NADH, FADH

Cytoplasmic membrane

out

in


ATP

H
+

H
+

H
+

H
+

H
+

H
+

O
2

H
2
O

1 Glucose


2 ATP

1 Glucose


38 ATP

Slow growth/low biomass yield

Fast growth/high biomass yield

Major functions of a fermentor

1) Provide operation free from contamination;

2) Maintain a specific temperature;

3) Provide adequate mixing and aeration;

4) Control the pH of the culture;

5) Allow monitoring and/or control of dissolved oxygen;

6) Allow feeding of nutrient solutions and reagents;

7) Provide access points for inoculation and sampling;

8) Minimize liquid loss from the vessel;

9) Facilitate the growth of a wide range of organisms.

(
Allman

A.R., 1999: Fermentation Microbiology and Biotechnology)

Microbial Growth Kinetics


Fermentation can be carried out as:

1.
Batch

2.
Continuous

3.
Fed
-
batch processes

Mode of operation is to a large extent dictated
by the type of product being produced.

Biotechnological processes of growing
microorganisms in a bioreactor

Batch Culture

Growth cycle of yeast
during beer
fermentation

From: Papazian C (1991), The New
Complete Joy of Home Brewing.

Alternate modes of energy generation

(H
2
S, H
2
, NH
3
)

(in autotrophs)

Fermentation

Fermentation

Fermentation Technology

-
> Process that produces
microbial cells (Biomass)
as a product




mainly for
-
> baking industry (yeast)


-
> human or animal food (microbial cells)


Fermentation Technology

Fermentation Technology


-
> Process that produces
microbial enzymes
as a product



mainly for
-
> food industry


Fermentation Technology

-
> Process that produces
microbial metabolites (primary or secondary)
as a
product





Fermentation Technology

-
> Process that produces
microbial metabolites (primary or secondary)
as a
product





Fermentation Technology

-
> Process that produces
microbial metabolites (primary or secondary)
as a
product





Fermentation Technology

-
> Process that produces
microbial metabolites (primary or secondary)
as a
product





Continuous cultures

Fed
-
Batch Culture

A
fed
-
batch

is a
biotechnological

batch

process which is based on feeding of a
growth limiting nutrient substrate to a
culture. The fed
-
batch strategy is
typically used in bio
-
industrial processes
to reach a high cell density in the
bioreactor
. Mostly the feed solution is
highly concentrated to avoid dilution of
the bioreactor. The controlled addition
of the nutrient directly affects the
growth rate of the culture and allows to
avoid
overflow metabolism

(formation
of side metabolites, such as
acetate

for
Escherichia coli
,
lactic acid

in cell
cultures,
ethanol

in
Saccharomyces

cerevisiae
), oxygen limitation
(
anaerobiosis
).

Batch culture versus continuous culture

Continuous systems: limited to single cell protein, ethanol productions, and
some forms of waste
-
water treatment processes.


Batch cultivation: the dominant form of industrial usage due to its many
advantages.


(Smith J.E, 1998: Biotechnology)

Advantages of batch culture versus
continuous culture

1)
Products may be required only in a small quantities at any given time.

2)
Market needs may be intermittent.

3)
Shelf
-
life of certain products is short.

4)
High product concentration is required in broth for optimizing downstream
processes.

5)
Some metabolic products are produced only during the stationary phase of the
growth cycle.

6)
Instability of some production strains require their regular renewal.

7)
Compared to continuous processes, the technical requirements for batch
culture is much easier.