352
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
much energy on a molar basis as the oxidation of carbohydrates. For
the complete aerobic oxidation of glucose to carbon dioxide,
C 6 H 12 0 6 + 60 2 = 6CO2 + 6H2O
the heat of combustion and the free energy change, respectively, are
—AH 298 ° = +673 kcal, and —AF° 298 ° = +694 kcal, per mole of
substrate.
2. Utilization of Energy for Biosynthesis: Free Energy Efficiency
a. Chemo-lithotrophic Bacteria. The chemo-lithotrophic way of life
is characterized by the twofold ability to utilize litho-oxidations as the
energy source and C0 2 as the sole carbon source; from this starting
material the organism, which can develop in a purely inorganic medium, carries out biosyntheses of all cell constituents. Carbon dioxide
fixation and assimilation is an endergonic process which requires at the
same time free energy and reducing systems, as shown schematically
by the equation
C0 2 + 4(H) + free energy = (CH 2 0) + 2 H 2 0
In this expression, where (H) indicates reducing capacity of any
origin, (CH 2 0) represents the organic matter which has been synthesized and corresponds to the fact that carbon in cell constituents is,
on the average, at the same degree of oxidation as it is in carbohydrates.
This classical representation obviously is approximative; according
to van Niel (9), the average degree of oxidation of the carbon
could be more exactly indicated by (C 2 H 3 0), at least in the photosynthetic bacteria of the family of Thiorhodaceae. From the point of
view of energetics, however, this comparison of the cell constituents
with the sugars is in satisfactory agreement with the experimental results. Baas-Becking and Parks (10) measured the heat of combustion
of several chemo-lithotrophic bacteria and found, on the average, 112
kcal, per gram-atom of carbon; this value is practically identical with
the heat of combustion of glucose calculated on the same basis, 113 kcal.
Similarly, Terroine and Wurmser (11) found 3480 cal. per gram of
mycelium in the heterotrophic mold Sterigmatocystis nigra, in close
agreement with the heat of combustion of a gram of glucose, 3700 cal.
The amount of energy incorporated in the cellular matter by chemoautotrophic bacteria may therefore be set at 113 kcal, per gram-atom of
carbon assimilated. From this value and the metabolic balance sheets of
the cultures, the energy efficiency can be calculated as follows:
Energy efficiency (%)
_
n
Carbon atoms assimilated X 113
Energy (kcal.) from amount of substrate oxidized
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
much energy on a molar basis as the oxidation of carbohydrates. For
the complete aerobic oxidation of glucose to carbon dioxide,
C 6 H 12 0 6 + 60 2 = 6CO2 + 6H2O
the heat of combustion and the free energy change, respectively, are
—AH 298 ° = +673 kcal, and —AF° 298 ° = +694 kcal, per mole of
substrate.
2. Utilization of Energy for Biosynthesis: Free Energy Efficiency
a. Chemo-lithotrophic Bacteria. The chemo-lithotrophic way of life
is characterized by the twofold ability to utilize litho-oxidations as the
energy source and C0 2 as the sole carbon source; from this starting
material the organism, which can develop in a purely inorganic medium, carries out biosyntheses of all cell constituents. Carbon dioxide
fixation and assimilation is an endergonic process which requires at the
same time free energy and reducing systems, as shown schematically
by the equation
C0 2 + 4(H) + free energy = (CH 2 0) + 2 H 2 0
In this expression, where (H) indicates reducing capacity of any
origin, (CH 2 0) represents the organic matter which has been synthesized and corresponds to the fact that carbon in cell constituents is,
on the average, at the same degree of oxidation as it is in carbohydrates.
This classical representation obviously is approximative; according
to van Niel (9), the average degree of oxidation of the carbon
could be more exactly indicated by (C 2 H 3 0), at least in the photosynthetic bacteria of the family of Thiorhodaceae. From the point of
view of energetics, however, this comparison of the cell constituents
with the sugars is in satisfactory agreement with the experimental results. Baas-Becking and Parks (10) measured the heat of combustion
of several chemo-lithotrophic bacteria and found, on the average, 112
kcal, per gram-atom of carbon; this value is practically identical with
the heat of combustion of glucose calculated on the same basis, 113 kcal.
Similarly, Terroine and Wurmser (11) found 3480 cal. per gram of
mycelium in the heterotrophic mold Sterigmatocystis nigra, in close
agreement with the heat of combustion of a gram of glucose, 3700 cal.
The amount of energy incorporated in the cellular matter by chemoautotrophic bacteria may therefore be set at 113 kcal, per gram-atom of
carbon assimilated. From this value and the metabolic balance sheets of
the cultures, the energy efficiency can be calculated as follows:
Energy efficiency (%)
_
n
Carbon atoms assimilated X 113
Energy (kcal.) from amount of substrate oxidized