March, 1914.] Soil Bacteria. 277 



Action of Bacteria upon Potash and Other Minerals. 



As a result of various bacterial activities, there is a production 

 of carbon dioxide (CO2) which, on being absorbed by soil water, 

 fomis a weak carbonic acid solution; it thus increases the solvent 

 action of water, and in this manner aids in rendering plant food 

 in an available form. Silicates of potash, unavailable to plants, 

 may be decomposed by carbonated water and in the presence of 

 lime the potassium siHcate may be converted into potassium 

 carbonate, a fomi of potash that is available to the plant. 



Another action of bacteria in dissolving mineral within the 

 soil is by their production of organic acids in decomposing htmius. 



The bacteria acting upon iron are not true bacteria, but be- 

 long to a higher thread like form. They deposit in the sheaths of 

 their cells quantities of ferrous hydroxide or ferrous oxide. They 

 grow in water charged with iron carbonate and are known to 

 •develop to such an extent in water pipes as to clog them with 

 ferrous hydroxide. 



When decomposition of anJmal and vegetable remains goes 

 on under anoerobic conditions, iron occurs as the sulphide when 

 under aerobic conditions, it occurs as ferrous carbonate. 



It is doubtful whether these organisms are essential in^ main- 

 taining a circulation of iron in the soil. 



Action of Bacteria in Relation to Sulphur. 



Usually sulphates are present in sufficient amounts within the 

 soil. They are taken by plants and converted into protein ma- 

 terial. Plants either die and decompose or are eaten by animals. 

 In the former case, as a result of bacterial decomposition of pro- 

 teids, hydrogen sulphide is produced. A group of sulphur oxidiz- 

 ing bacteria (Beggiatoa), which are thread hke, oxidizes the 

 hydrogen sulphide (HoS) to furnish energy, and store up sulphur 

 in its cells. When the hydrogen sulphide becomes diminished, 

 these bacteria oxidize the sulphur, which then becomes sulphur 

 dioxide (SO,). They do this without the aid of light or any 

 pigment. Another colorless group of sulphur bacteria is Thiotrix. 



Other forms of sulphur bacteria are red pigmented, the red 

 pigment being analogous to the action of chlorophyll in plants. 

 These bacteria require light for growth. They occur abundantly 

 in sea water near the shore. The red color occasioned by the de- 

 velopment of bacteria has given the Red Sea its name. 



There probably are certain bacteria that act upon phosphorous. 

 In the decomposition of proteid material (of which phosphorous 

 is a component) there are two end products, under anaerobic 

 conditions the end product is phosphein (H3P) ; under aerobic 

 conditions the end product is phosphoric acid (P2O5). 



