398
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
gradually take on a brown-red color by incrustation of iron and manganese oxides. The filamentous ferrobacteria grow in sometimes considerable quantities in cold chalybeate springs or in water pipes where they
may completely seal off the opening with their characteristic sticky, reddish mass. Pringsheim (204) took up critically the investigation of the
many forms classified in distinct genera and species and showed that
most of them are morphological variants belonging to only two different species, Sphaerotilus discophorus and S. natans.
The organism which was described by Ehrenberg (198) as Gallionella and which retained this generic name belongs to the Caulobacteriales or stalk bacteria. They are short, immobile, Gram-negative,
curved inward like a comma or kidney bean. They attach themselves
to solid surfaces by means of a coiled stalk which is secreted by their
concave lateral edge and becomes impregnated progressively with a
brown-red precipitate of ferric hydroxide.
The nutrition of the ferrobacteria has long been the subject of a
controversy which continues to this day. Winogradsky (199) considered
them to be chemo-lithotrophs which use the oxidation of ferrous to
ferric iron as their sole energy source. However, Molisch (201) insisted
that they could grow on peptone media in the presence or absence of
iron, and classified them as heterotrophs in which the oxidation of iron
is conditional and plays no metabolic role. Lieske (202) returned to the
opinion of Winogradsky at least with regard to Gallionella and suggested that the development of this organism was based on the oxidation
of ferrous carbonate by the following reaction:
4FeC0 3 + 0 2 + 6H 2 0 = 4Fe(OH) 3 + 4C0 2
(-AF° 298 = 40 kcal.)
Several authors tried to provide experimental evidence for the
chemo-autotrophy of the ferrobacteria but these attempts, evaluated
critically by Pringsheim (204), Cataldi (206), and Starkey (207), were
not conclusive. In fact, most of the organisms were studied in impure
cultures and on nonsynthetic media. Since the ferrobacteria grow near
neutral pH levels and under these conditions iron is rapidly oxidized by
the oxygen of the air, the culture media routinely contained proteins or
humic acids, in order to stabilize ferrous iron, and it could not be excluded that growth was actually due to these organic components.
Moreover, Starkey (207), on the basis of the feebly exergonic nature of
the reaction, felt that the possibility of autotrophic development of the
ferrobacteria was slim and that if it really existed, one might expect a
500:1 ratio by weight between iron oxidized and cellular matter
synthesized.
However, Sartory and Mayer (208) have been able to isolate Galli-
CLAUDE FROMAGEOT AND JACQUES C. SENEZ
gradually take on a brown-red color by incrustation of iron and manganese oxides. The filamentous ferrobacteria grow in sometimes considerable quantities in cold chalybeate springs or in water pipes where they
may completely seal off the opening with their characteristic sticky, reddish mass. Pringsheim (204) took up critically the investigation of the
many forms classified in distinct genera and species and showed that
most of them are morphological variants belonging to only two different species, Sphaerotilus discophorus and S. natans.
The organism which was described by Ehrenberg (198) as Gallionella and which retained this generic name belongs to the Caulobacteriales or stalk bacteria. They are short, immobile, Gram-negative,
curved inward like a comma or kidney bean. They attach themselves
to solid surfaces by means of a coiled stalk which is secreted by their
concave lateral edge and becomes impregnated progressively with a
brown-red precipitate of ferric hydroxide.
The nutrition of the ferrobacteria has long been the subject of a
controversy which continues to this day. Winogradsky (199) considered
them to be chemo-lithotrophs which use the oxidation of ferrous to
ferric iron as their sole energy source. However, Molisch (201) insisted
that they could grow on peptone media in the presence or absence of
iron, and classified them as heterotrophs in which the oxidation of iron
is conditional and plays no metabolic role. Lieske (202) returned to the
opinion of Winogradsky at least with regard to Gallionella and suggested that the development of this organism was based on the oxidation
of ferrous carbonate by the following reaction:
4FeC0 3 + 0 2 + 6H 2 0 = 4Fe(OH) 3 + 4C0 2
(-AF° 298 = 40 kcal.)
Several authors tried to provide experimental evidence for the
chemo-autotrophy of the ferrobacteria but these attempts, evaluated
critically by Pringsheim (204), Cataldi (206), and Starkey (207), were
not conclusive. In fact, most of the organisms were studied in impure
cultures and on nonsynthetic media. Since the ferrobacteria grow near
neutral pH levels and under these conditions iron is rapidly oxidized by
the oxygen of the air, the culture media routinely contained proteins or
humic acids, in order to stabilize ferrous iron, and it could not be excluded that growth was actually due to these organic components.
Moreover, Starkey (207), on the basis of the feebly exergonic nature of
the reaction, felt that the possibility of autotrophic development of the
ferrobacteria was slim and that if it really existed, one might expect a
500:1 ratio by weight between iron oxidized and cellular matter
synthesized.
However, Sartory and Mayer (208) have been able to isolate Galli-