PURE CULTURE STUDY OF SOIL BACTERIA 59 



II. Growth similar to the Eubacteria, but cells containing bacteriopurpurin 

 (and bacteriochlorin), being colored rose, red or violet. Order Rhodo- 



BACTERIA. 



III. Colorless bacteria accumulating sulfur within their cells. Order Thio- 



BACTERIA. 



IV. Alga-like bacteria. Order Phycobacteria. This order comprises the 



family Chlamydobacteriaceae which form sheaths; these include the 



iron bacteria. 17 

 V. Fungus-like bacteria, rod-shaped, rarely filamentous. Order Mycobacteria. 



The Actinomyces are frequently included in this genus. 

 VI. Bacterial cells enclosed in a slimy mass, forming a pseudoplasmodium-like 



aggregation before passing into a cyst-producing resting stage. Order 



Myxobacteria. 



Classification of soil bacteria based upon their physiological activities 1 * 



I. Autotrophic and facultative autotrophic bacteria, deriving their carbon 

 primarily from the C0 2 of the atmosphere and their energy from the 

 oxidation of inorganic substances or simple compounds of carbon. 



1. Bacteria using nitrogen compounds as sources of energy: 



(a) Nitrite forming bacteria. 



(b) Nitrate forming bacteria. 



2. Bacteria using sulfur and sulfur compounds as sources of energy. 



3. Bacteria using iron (and manganese) compounds as sources of energy. 



4. Bacteria using simple carbon compounds as sources of energy: 



(a) Bacteria oxidizing carbon monoxide. 



(b) Bacteria oxidizing methane. 



5. Bacteria using hydrogen as a source of energy. 



II. Heterotrophic bacteria deriving their carbon and energy from various 

 organic compounds: 

 1. Nitrogen-fixing bacteria, deriving their nitrogen from the atmosphere, 

 in the form of gaseous atmospheric nitrogen: 



a. Non-symbiotic nitrogen-fixing bacteria: 



(a) Anaerobic types: Butyric acid bacteria {Bac. amylobacler) , 



including species of Clostridium, Granulobacter, etc. 



(b) Aerobic types: Azotobacter, Radiobacter, Bad. aerogenes, 



Bad. pneumoniae, etc. 



b. Symbiotic nitrogen-fixing (nodule) bacteria. 



17 A detailed review of "The generic names of bacteria" is given by E. M. A. 

 Enlows. Hyg. Lab. Bui. 121. Washington, D. C, 1920; Buchanan, R. E. 

 Systematic bacteriology. 1925. 



18 A detailed system of bacteria based on biochemical relationships has been 

 proposed by Orla-Jensen— Die Hauptlinien des natiirlichen Bakteriensystems. 

 Centrbl. Eakt. II, 22: 305 346. 1909. 



