oxidation results in formation of mineral compounds
(CO 2 , H 2 O, NH 3 , etc.). In this case, it is called a process
of mineralization of organic sources.
Products of oxidation may remain inside the cell or be
excreted out in the form of wastes. Thus, the chemoorganotrophic microorganisms are the decomposers of
organic matter and ensure the progressive mineralization
of organic matter, releasing mineral compounds in external environment (CO 2 , NH 3 , NO 3
À , PO 4
3À , SO 4
2À , HS
À
).
2. The
source
of
energy
can
be
inorganic
(chemolithotrophic microorganisms*), consisting of
reduced inorganic compounds such as dihydrogen, nitrogen or sulfur compounds, metals, etc.
3. The energy source can also be photonic (light) in the case
of photosynthetic* or phototrophic microorganisms*
which have pigments and photosynthetic systems able to
react under the light action, thus converting light energy
into chemical energy.
As sources of cellular constituents, the simple organic
molecules produced in the cell or from the external environment are used as the basis of biosynthetic activities:
1. For most microorganisms, carbon organic compounds are
required; these microorganisms are considered as
heterotrophs*. They can use of low-weight organic
molecules produced in energy reactions of degradation
or taken from the environment.
2. Other microorganisms use CO 2 as sole carbon source to
synthesize all their cellular components; these are autotrophic microorganisms* using a mineral source of
energy (chemolithotrophic microorganisms) or light
(phototrophic microorganisms).
In summary, several nutritional types are defined in
microorganisms:
1. The energy source is:
• Chemical: chemotrophic microorganisms using an
organic source (chemoorganotrophs*) or an inorganic source (chemolithotrophs*)
• Photonic: phototrophic microorganisms using an
organic compound (photoorganotrophs*) or a mineral compound (photolithotrophs*) as a source of
electrons
2. The carbon source is a compound:
• Organic: heterotrophs
• Mineral (CO 2 ): autotrophs
Cellular metabolism is formed by means of the redox
reactions in catabolism for energy production (energy
metabolism) and the reactions of biosynthesis necessary for
anabolism (production of cellular components) (Fig. 3.8). To
be functional and viable, a cell should maintain its internal
environment in a reduced state in order to ensure cohesion
and structure of macromolecules. For this, it must constantly
produce energy and reducing power* during chemical or
Cellular constituents
CYTOPLASM
OUTER ENVIRONMENT
Energy-rich
compounds
Small organic molecules,
products of mineralization
E n e r g y
p r o d u c ti o n
C a t a
b o l i s m
A n a b o li s m
B io s y n th e si s
Nutrients
(organic and
inorganic
compounds)
Organic or
mineral wastes
Fig. 3.7 Role of nutrients in cell metabolism (Drawing: M.-J. Bodiou)
34
R. Matheron and P. Caumette
(CO 2 , H 2 O, NH 3 , etc.). In this case, it is called a process
of mineralization of organic sources.
Products of oxidation may remain inside the cell or be
excreted out in the form of wastes. Thus, the chemoorganotrophic microorganisms are the decomposers of
organic matter and ensure the progressive mineralization
of organic matter, releasing mineral compounds in external environment (CO 2 , NH 3 , NO 3
À , PO 4
3À , SO 4
2À , HS
À
).
2. The
source
of
energy
can
be
inorganic
(chemolithotrophic microorganisms*), consisting of
reduced inorganic compounds such as dihydrogen, nitrogen or sulfur compounds, metals, etc.
3. The energy source can also be photonic (light) in the case
of photosynthetic* or phototrophic microorganisms*
which have pigments and photosynthetic systems able to
react under the light action, thus converting light energy
into chemical energy.
As sources of cellular constituents, the simple organic
molecules produced in the cell or from the external environment are used as the basis of biosynthetic activities:
1. For most microorganisms, carbon organic compounds are
required; these microorganisms are considered as
heterotrophs*. They can use of low-weight organic
molecules produced in energy reactions of degradation
or taken from the environment.
2. Other microorganisms use CO 2 as sole carbon source to
synthesize all their cellular components; these are autotrophic microorganisms* using a mineral source of
energy (chemolithotrophic microorganisms) or light
(phototrophic microorganisms).
In summary, several nutritional types are defined in
microorganisms:
1. The energy source is:
• Chemical: chemotrophic microorganisms using an
organic source (chemoorganotrophs*) or an inorganic source (chemolithotrophs*)
• Photonic: phototrophic microorganisms using an
organic compound (photoorganotrophs*) or a mineral compound (photolithotrophs*) as a source of
electrons
2. The carbon source is a compound:
• Organic: heterotrophs
• Mineral (CO 2 ): autotrophs
Cellular metabolism is formed by means of the redox
reactions in catabolism for energy production (energy
metabolism) and the reactions of biosynthesis necessary for
anabolism (production of cellular components) (Fig. 3.8). To
be functional and viable, a cell should maintain its internal
environment in a reduced state in order to ensure cohesion
and structure of macromolecules. For this, it must constantly
produce energy and reducing power* during chemical or
Cellular constituents
CYTOPLASM
OUTER ENVIRONMENT
Energy-rich
compounds
Small organic molecules,
products of mineralization
E n e r g y
p r o d u c ti o n
C a t a
b o l i s m
A n a b o li s m
B io s y n th e si s
Nutrients
(organic and
inorganic
compounds)
Organic or
mineral wastes
Fig. 3.7 Role of nutrients in cell metabolism (Drawing: M.-J. Bodiou)
34
R. Matheron and P. Caumette