364
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
A third molecule of ATP is consumed in the phosphorylation of ribulose5-phosphate to ribulose-l,5-diphosphate.
Aubert et al. (29) showed that in T. denitriftcans the synthesis of
ribulose diphosphate from ribulose monophosphate requires ATP, and
that the oxidation of thiosulfate is coupled to the formation of ATP.
The mechanism by which ATP is produced is unknown. Recent experiments of Vishniac and Santer (88) and Skarzynski and Ostrowski (39)
showed that during the oxidation of thiosulfate by T. thioparus intermediate compounds appear which contain both sulfur and phosphorus
but whose chemical nature is not yet known.
The transfer of electrons from the litho-oxidative reaction to the
biosynthetic pathway is probably mediated by a complex system involving cytochromes. As discussed below, several authors have demonstrated that thiobacilli contain cytochromes, some of which are of the
type c, which are reduced by thiosulfate in the presence of cell-free
bacterial extracts. The electrons needed for the reduction of 3-phosphoglyceric acid are doubtless transferred from these cytochromes to the
substrate by the pyridine nucleotides.
Although information is not yet available on the mechanism of C0 2
fixation in other autotrophic bacteria and particularly in nitrifying bacteria, it is likely that these organisms behave in a manner analogous or
identical to the thiobacilli and the hydrogen bacteria. The chemo-lithotrophic bacteria thus seem to be bridge organisms in which the biosynthetic systems of chlorophyll-containing plants and of higher animals are united. These facts are of great interest in comparative biochemistry since they demonstrate the remarkable similarity in the
processes of intermediary carbon metabolism and of energy transport
systems found in all living beings.
D. INTERRELATIONS BETWEEN THE CHEMO-LITHOTROPHIC
AND HETEROTROPHIC MODES OF NUTRITION
The chemo-lithotrophic bacteria fall into two groups with regard to
their behavior toward exogenous organic matter. The first group, comprising only the nitrifying bacteria and most of the thiobacilli, is that of
the strict or obligatory autotrophs, i.e., organisms incapable of using
any form of organic matter as either the source of energy or of carbon.
The second group, featuring particularly the hydrogen bacteria, is that
of the facultative autotrophs, which can grow either autotrophically on
a purely inorganic medium or heterotrophically on various organic
compounds.
Winogradsky and Omeliansky (40) observed that nitrifying bacteria
not only are unable to utilize organic substrates but are actually inhibited by low concentrations of glucose, peptone, asparagine, or so-
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
A third molecule of ATP is consumed in the phosphorylation of ribulose5-phosphate to ribulose-l,5-diphosphate.
Aubert et al. (29) showed that in T. denitriftcans the synthesis of
ribulose diphosphate from ribulose monophosphate requires ATP, and
that the oxidation of thiosulfate is coupled to the formation of ATP.
The mechanism by which ATP is produced is unknown. Recent experiments of Vishniac and Santer (88) and Skarzynski and Ostrowski (39)
showed that during the oxidation of thiosulfate by T. thioparus intermediate compounds appear which contain both sulfur and phosphorus
but whose chemical nature is not yet known.
The transfer of electrons from the litho-oxidative reaction to the
biosynthetic pathway is probably mediated by a complex system involving cytochromes. As discussed below, several authors have demonstrated that thiobacilli contain cytochromes, some of which are of the
type c, which are reduced by thiosulfate in the presence of cell-free
bacterial extracts. The electrons needed for the reduction of 3-phosphoglyceric acid are doubtless transferred from these cytochromes to the
substrate by the pyridine nucleotides.
Although information is not yet available on the mechanism of C0 2
fixation in other autotrophic bacteria and particularly in nitrifying bacteria, it is likely that these organisms behave in a manner analogous or
identical to the thiobacilli and the hydrogen bacteria. The chemo-lithotrophic bacteria thus seem to be bridge organisms in which the biosynthetic systems of chlorophyll-containing plants and of higher animals are united. These facts are of great interest in comparative biochemistry since they demonstrate the remarkable similarity in the
processes of intermediary carbon metabolism and of energy transport
systems found in all living beings.
D. INTERRELATIONS BETWEEN THE CHEMO-LITHOTROPHIC
AND HETEROTROPHIC MODES OF NUTRITION
The chemo-lithotrophic bacteria fall into two groups with regard to
their behavior toward exogenous organic matter. The first group, comprising only the nitrifying bacteria and most of the thiobacilli, is that of
the strict or obligatory autotrophs, i.e., organisms incapable of using
any form of organic matter as either the source of energy or of carbon.
The second group, featuring particularly the hydrogen bacteria, is that
of the facultative autotrophs, which can grow either autotrophically on
a purely inorganic medium or heterotrophically on various organic
compounds.
Winogradsky and Omeliansky (40) observed that nitrifying bacteria
not only are unable to utilize organic substrates but are actually inhibited by low concentrations of glucose, peptone, asparagine, or so-