The physiology and morphology of iron- and manganese-depositing flagellates are investigated by means of cultural experiments, with special reference to
Anthophysa vegetans
Stein,
Siderodendron manganiferum
n.gen., n.sp.,
Siphomonas Fritschii
n.gen., n.sp. and
Bikosoeca
(
Poteriodendron
)
petiolata
(Stein) n.comb.
Anthophysa
multiplies in various liquid media containing small amounts of organic substances, hay decoction being specially favourable. Still better results are achieved with soil-water cultures, which afford the only successful cultures of
Siderodendron
and
Siphomonas
, while
Bikosoeca
also grows well in hay infusions. Addition of Fe" and Mn" is essential. The brown colour of biological iron deposits is shown to be due to admixture of manganese compounds, while mere ferric precipitates are in microscopical amounts almost colourless.
Anthophysa
and
Siderodendron
deposit more manganese than iron, so that their stalks appear brown, while those of
Siphomonas
are generally light brown. The envelopes of
Bikosoeca
are almost entirely composed of ferric compounds and appear colourless or faintly yellowish. All four organisms exhibit various modifications according to the habitat conditions. The formation of stalks and envelopes respectively depends on the availability of the relevant metals in the form of lower oxides, but the organisms here described can also exist without producing these structures. The oxidation of ferrous and manganese compounds is catalysed by the cells of these flagellates, although the role of this process in the cellular metabolism is not known. Nutrition is holozoic, chiefly by ingestion of bacteria. Like other holozoic flagellates these organisms cannot exist in the presence of an abundant bacterial vegetation owing to the resulting lack of oxygen. They thrive in quiet, well-aerated waters, with a small content of organic substances, above zones in which Fe and Mn compounds are reduced and from which ferrous and manganous compounds diffuse to the overlying oxidation zone, where these flagellates deposit Fe"' and Mn'" in a morphologically defined form. ‘Iron’ flagellates generally live in association and competition with iron bacteria of the
Leptothrix
group, the removal of which produces much better growth. A description of the relevant flagellates and of their appearance under various conditions, as well as diagnoses of
Siderodendron
and
Siphomonas
, are given.
On iron flagellates
