244 Transformation of Mineral Substances 



Transformation of Other Elements 



In addition to the above elements, a variety of others either are 

 subject to transformation by microorganisms or play a part in their 

 metabolism. It is sufficient to mention hydrogen, oxygen, and silicon. 



Hydrogen enters into the composition of microbial cells in the 

 form of water. It forms an important part of the various organic 

 and inorganic constituents of the microbial cell. It is subject also 

 to characteristic oxidation reactions by specific bacteria, considerable 

 energy being liberated in this reaction: 



H2 + O = HoO 



Oxygen is highly important in all biological reactions, including 

 both anaerobic (fermentation) and aerobic (respiration) processes. 

 It is important in cell synthesis and in organic matter decomposition. 

 Without it, no life would exist. 



Silicon is present abundantly in the mineral framework of the 

 soil. It is found extensively in the cell substance of many soil organ- 

 isms, notably the diatoms, certain protozoa, fungi, and bacteria. 

 Silicon undergoes various transformations as a result of the direct 

 and indirect activities of microorganisms. When plant residues are 

 decomposed, silicon is liberated as silica and is allowed to accumu- 

 late. Silica may be rendered soluble through the action of carbon 

 dioxide and through the organic and inorganic acids produced by 

 microorganisms. This plays an essential role in rock weathering and 

 soil formation. 



The action of microorganisms on silica has been little studied, even 

 though a high silica content is found in the stems of various plants. 

 In the cereals the rigidity of the straw is largely due to silica. An 

 abundance of sodium nitrate added to the soil was found to depress 

 the silica content of straw. 



Selected Bibliograi)hy 



1. Fred, E. B., and Haas, A. R. C, The- ctcliing of inarhlr In roots in tlie pres- 

 ence'of bacteria, J. Gen. Physiol., 1:631-638, 1919. 



2. Gerretsen, F. C, Manganese deficiency of oats and its relation to soil bac- 

 ^ teria, Ann. Botamj, N.S., 1:207-230, 1937. 



