Bacteria and Iron 



801 



the oxidation of sulfurstted hydrogen 

 by the sulfur bacteria. The sulfur is 

 not used by the latter as a food, but 

 only as a fuel— a source of energy. Simi- 

 larly, in the case of the iron bacteria, 

 the iron which is made to take on 

 oxygen serves as a source of fuel. In 

 the one case, the final product is sul- 

 furic acid, which passes out of the bac- 

 terial cells. In the other, a soluble 

 compound, or compounds, of iron 

 passes into the outer sheath of the 

 microorganisms. 



The importance of iron bacteria. — 

 The iron bacteria, represented chiefly 

 by Cladothrix dichotoma and Crenothrix 

 Kiihniana, have played in the past and 

 are playing in the present a role of 

 considerable significance in the accumu- 

 lation and migration of iron compounds 

 in certain localities. This applies par- 

 ticularly to swamps, meadows and 

 marshes n which deposits of bog iron 

 are, at t mes, formed. Soluble com- 

 pounds of iron of a lower state of oxida- 

 tion are carried to such places and are 

 there made to combine with more oxy- 

 gen, partly through the activities of 

 iron bacteria. One of these soluble 

 compounds of iron, known as ferrous 

 sulfate, or copperas, is a substance quite 



v.. 



t) 



Fig. 57. Iron bacteria. 

 1. Bog iron. 2. 

 Psichohormium an- 

 tliarium, showing 

 masses of iron sur- 

 rounding the cell- 

 walls. 3. The same, 

 after treatment 

 with dilute acid; 

 X 600. (Mo-Hsh.) 



