io8 
Iron-Bacteria. 
vital activity of the organism. As has been already mentioned, 
Winogradsky held the same view with regard to Leptothrix ochracea. 
He observed that the gelatinous sheath which surrounds the 
filaments in this form continued to accumulate iron only where it 
enclosed a living cell; and as his culture fluid contained only 
minute traces of organic substances it seemed unlikely that these 
would be sufficient for the organism apart from the energy obtained 
by active oxidation of iron. Lieske has repeated Winogradsky’s 
culture experiments and confirms his main results. As he found 
Leptothrix growing in nature in water in which he could detect no 
organic material he is inclined to the view that Leptothrix , like 
Spirophyllum, can live autotrophically, in absence of organic nutrient 
substances, by the oxidation of iron. On the other hand he was 
able, like Molisch, to cultivate the same species on peptone-gelatine 
media containing manganese, but no iron. Molisch succeeded 
further in cultivating it on organic media without either iron or 
manganese. This form thus differs from Spirophyllum in being 
able, apparently, to live either heterotrophically or autotrophically. 
How far Leptothrix makes use of its heterotrophic capabilities in 
nature is uncertain: Lieske never found either this or any other 
iron bacterium in iron springs with a high organic content. 
No evidence is available as to the precise way in which the 
oxidation of ferrous carbonate is effected or how the energy so 
liberated is utilised. Whether the carbon required for the growth 
of the organism is obtained direct from ferrous carbonate or as free 
C0. 2 can scarcely be determined. C0 2 could not be assimilated in 
absence of iron for want of the necessary energy; and it is 
impossible to supply ferrous carbonate without at the same time 
supplying free C0 2 , for ferrous carbonate in solution undergoes 
hydrolytic dissociation. Quantitative experiments, too, present 
difficulties which Lieske has not been able to overcome. 
Finally, Lieske’s observations and experiments throw an 
interesting light on the biology of iron-bacteria. The occurrence of 
the different forms is affected by temperature as well as by the 
presence of iron. Spirophyllum flourishes even at 0°C, in brooks 
partly covered with ice, and grows most luxuriantly at 6°. At 22° 
on the other hand little growth occurs, and at 27° it ceases 
altogether to develop. In consequence of this Lieske was unable 
to find any trace of Spirophyllum in the warm summer months. 
Leptothrix is to be found growing well at all seasons of the year, 
and temperature seems to affect its rate of growth but little; while 
other forms ( Clonothrix , Crenothrix) grow best when the water is 
warmest (18—25"C), disappearing altogether when the cooler 
weather approaches. D. T. 
LITERATURE. 
Winogradsky, Ueber Eisenbakterien. Rot. Zeit., 1888, p. 261. 
Molisch, Die Eisenbakterien. Jena, 1910. 
Lieske, Beitrage zur Kenntnis der Physiologie von Spirophyllum ferrugineum 
Ellis, einem typischen Eisenbakterium. Jahrb. f.vviss. Bot., 1911, 
p. 91. 
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