366
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
In this connection it is of interest that Rittenberg and Grady (54), by
ultraviolet irradiation of a normal strain of Γ. thiooxidans, obtained
auxotrophic mutants which had lost a part of their biosynthetic capabilities and which grew only on a medium supplemented with thiamine
or yeast extract.
It has long been held that autotrophic and heterotrophic modes of
nutrition cannot coexist in facultative autotrophs. This opinion was
based on the observations of Niklevskii (55) and Ruhland (56) who
found that the presence of an utilizable organic substrate in the culture
medium completely suppresses the consumption of hydrogen by Hydrogenomonas. Kluyver and Manten (57) reported later that cells of H.
flava grown on organic media are effectively devoid of hydrogenase,
but that cells derived from cultures grown on inorganic media oxidize
lactate and H 2 simultaneously and in an additive fashion, indicating
that coexistence of the two modes of nutrition in the cell is indeed
possible. More recently, Wilson et al. (58) showed that if cultures are
maintained at a partial pressure of oxygen below 5%, the presence of
metabolizable organic substrates in the medium exerts no inhibition on
the formation of hydrogenase by cells of H. facilis; under these conditions, lactate and H 2 are consumed simultaneously.
II. Oxidation of Nitrogen Compounds
In theory, there ought to be numerous inorganic forms of nitrogen
which can be oxidized in biological systems and which could thus serve
as energy sources for growth of chemo-lithotrophic organisms. As
pointed out by Baas-Becking and Parks (JO), it might be expected a
priori that there are organisms which can utilize for their growth the
energy produced by the aerobic oxidation of N 2 to nitrate, or of NH 3 to
N 2 . But such biological systems have never been demonstrated and
their existence is very unlikely since these oxidations are not very exergonic and, with regard to the oxidation of N 2 , the required activation
of the biatomic gaseous molecule would entail a considerable expenditure of energy (225 kcal./mole).
In fact, the only known type of nitrogen litho-oxidation is the process of nitrification, i.e., the aerobic oxidation of an ammonium ion to
nitrite and nitrate.
A. NITRIFYING MICROORGANISMS
1. Chemo-lithotrophic Nitrifying Bacteria
The biological oxidation of ammonia in the soil was demonstrated
by Schloesing and Muntz (59) in 1877. However, it was some years
later, in 1890, that Winogradsky (60) isolated and described two of
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
In this connection it is of interest that Rittenberg and Grady (54), by
ultraviolet irradiation of a normal strain of Γ. thiooxidans, obtained
auxotrophic mutants which had lost a part of their biosynthetic capabilities and which grew only on a medium supplemented with thiamine
or yeast extract.
It has long been held that autotrophic and heterotrophic modes of
nutrition cannot coexist in facultative autotrophs. This opinion was
based on the observations of Niklevskii (55) and Ruhland (56) who
found that the presence of an utilizable organic substrate in the culture
medium completely suppresses the consumption of hydrogen by Hydrogenomonas. Kluyver and Manten (57) reported later that cells of H.
flava grown on organic media are effectively devoid of hydrogenase,
but that cells derived from cultures grown on inorganic media oxidize
lactate and H 2 simultaneously and in an additive fashion, indicating
that coexistence of the two modes of nutrition in the cell is indeed
possible. More recently, Wilson et al. (58) showed that if cultures are
maintained at a partial pressure of oxygen below 5%, the presence of
metabolizable organic substrates in the medium exerts no inhibition on
the formation of hydrogenase by cells of H. facilis; under these conditions, lactate and H 2 are consumed simultaneously.
II. Oxidation of Nitrogen Compounds
In theory, there ought to be numerous inorganic forms of nitrogen
which can be oxidized in biological systems and which could thus serve
as energy sources for growth of chemo-lithotrophic organisms. As
pointed out by Baas-Becking and Parks (JO), it might be expected a
priori that there are organisms which can utilize for their growth the
energy produced by the aerobic oxidation of N 2 to nitrate, or of NH 3 to
N 2 . But such biological systems have never been demonstrated and
their existence is very unlikely since these oxidations are not very exergonic and, with regard to the oxidation of N 2 , the required activation
of the biatomic gaseous molecule would entail a considerable expenditure of energy (225 kcal./mole).
In fact, the only known type of nitrogen litho-oxidation is the process of nitrification, i.e., the aerobic oxidation of an ammonium ion to
nitrite and nitrate.
A. NITRIFYING MICROORGANISMS
1. Chemo-lithotrophic Nitrifying Bacteria
The biological oxidation of ammonia in the soil was demonstrated
by Schloesing and Muntz (59) in 1877. However, it was some years
later, in 1890, that Winogradsky (60) isolated and described two of