374
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
When the sulfide initially present has disappeared from the medium,
the bacteria carry out the oxidation of S° to sulfate:
S° + 1.5 0 2 + H 2 0 = H 2 S0 4 + 118 kcal.
so that the intracellular sulfur granules may be considered to some
extent as nutritive and energy-yielding reserves.
According to Winogradsky (90), Beggiatoa is an autotroph which
uses sulfides and C0 2 as sole carbon and energy sources. This opinion
is also held by Keil (91) but rejected by others. Certain experiments of
Cataldi (92), in fact, suggest that at least some strains of Beggiatoa cannot grow in the complete absence of organic matter and are therefore
heterotrophic organisms.
3. Photosynthetic Sulfo-oxidizing Bacteria
The essential physiological characteristics of these organisms, which
include the purple sulfur bacteria (or Thiorhodaceae) and the green
sulfur bacteria (or Chlorobacteriaceae) were described in Section I of
this chapter. It was pointed out in particular that van Niel (17) and
Larsen (18) showed that these organisms use only inorganic sulfur
compounds as electron donors in their characteristic type of photosynthesis and that they cannot utilize the free energy produced by the oxidation of their inorganic substrates for biosynthetic reactions.
Each of the two families, the Thiorhodaceae and the Chlorobacteriaceae, comprise several genera and species whose morphological
characteristics and taxonomic relationships were analyzed by Bisset and
Grace (62). Most of the types which have been described are not well
known and in some instances it is even doubtful whether they exist at
all. Van Niel (17) showed that several forms thought to be distinct
species are in reality interconvertible if the developmental conditions are
modified and actually belong to a restricted number of different types.
Almost everything known about the metabolism of the photosynthetic sulfur bacteria concerns the genus Chromatium among the purple
bacteria and the genus Chlorobium among the green bacteria. Larsen
(93) isolated and described two species of the latter which were identical morphologically but behaved differently toward inorganic sulfur
compounds. The two species, C. UmicoL· and C. thiosulfatophilum, oxidize sulfides to elementary sulfur in the light under complete anaerobiosis at pH 7.5; the sulfur precipitates in the exocellular medium
light
C0 2 + 2H 2 S
► (CH 2 0) + 2S° + H 2 0
Then, in a second step, they carry out oxidation to sulfate
light
3C0 2 + 2S° + 5H 2 0
> 3(CH 2 0) + 2H 2 S0 4
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
When the sulfide initially present has disappeared from the medium,
the bacteria carry out the oxidation of S° to sulfate:
S° + 1.5 0 2 + H 2 0 = H 2 S0 4 + 118 kcal.
so that the intracellular sulfur granules may be considered to some
extent as nutritive and energy-yielding reserves.
According to Winogradsky (90), Beggiatoa is an autotroph which
uses sulfides and C0 2 as sole carbon and energy sources. This opinion
is also held by Keil (91) but rejected by others. Certain experiments of
Cataldi (92), in fact, suggest that at least some strains of Beggiatoa cannot grow in the complete absence of organic matter and are therefore
heterotrophic organisms.
3. Photosynthetic Sulfo-oxidizing Bacteria
The essential physiological characteristics of these organisms, which
include the purple sulfur bacteria (or Thiorhodaceae) and the green
sulfur bacteria (or Chlorobacteriaceae) were described in Section I of
this chapter. It was pointed out in particular that van Niel (17) and
Larsen (18) showed that these organisms use only inorganic sulfur
compounds as electron donors in their characteristic type of photosynthesis and that they cannot utilize the free energy produced by the oxidation of their inorganic substrates for biosynthetic reactions.
Each of the two families, the Thiorhodaceae and the Chlorobacteriaceae, comprise several genera and species whose morphological
characteristics and taxonomic relationships were analyzed by Bisset and
Grace (62). Most of the types which have been described are not well
known and in some instances it is even doubtful whether they exist at
all. Van Niel (17) showed that several forms thought to be distinct
species are in reality interconvertible if the developmental conditions are
modified and actually belong to a restricted number of different types.
Almost everything known about the metabolism of the photosynthetic sulfur bacteria concerns the genus Chromatium among the purple
bacteria and the genus Chlorobium among the green bacteria. Larsen
(93) isolated and described two species of the latter which were identical morphologically but behaved differently toward inorganic sulfur
compounds. The two species, C. UmicoL· and C. thiosulfatophilum, oxidize sulfides to elementary sulfur in the light under complete anaerobiosis at pH 7.5; the sulfur precipitates in the exocellular medium
light
C0 2 + 2H 2 S
► (CH 2 0) + 2S° + H 2 0
Then, in a second step, they carry out oxidation to sulfate
light
3C0 2 + 2S° + 5H 2 0
> 3(CH 2 0) + 2H 2 S0 4