158 PRINCIPLES OF SOIL MICROBIOLOGY 



fying bacteria. 49 The nature of the medium was found 50 to have an 

 important influence upon the temperature optimum of the organism. 

 Two per cent of glucose is added to soil either alone or with 2 per 

 cent CaC0 3 ; this is then steamed at 100° for 20 minutes, to kill the 

 non-spore-forming organisms. Water is added to bring the moisture 

 to 16 per cent and the soils are incubated at 52°C. for 4 to 6 days, at 

 which time the bacteria are isolated. These bacteria grow in media 

 at 52°C, but not at 28° to 30°; when reinoculated into soil, they may 

 grow well even at 15° to 20° although not so abundantly. Miehe 

 assumed that these organisms can develop only in manure heaps where 

 a great deal of heat is generated. However, others 50 suggested that 

 they do not always lead a latent life in the soil, but find in summer a 

 suitable temperature for their development. 51 Among the activities 

 of the thermophilic bacteria, the decomposition of organic matter, 

 especially the decomposition of celluloses in manure, occupies the first 

 place. Many of the bacteria are strongly proteolytic. Most of them 

 are strictly aerobic and form spores. Some organisms are facultative 

 thermophilic, since they can grow at 20°, have their optimum at 50°C. 

 and maximum at about G0°C. 52 



Mycobacteria. The Mycobacteria are a group of organisms which 

 differ from true bacteria by the formation of more or less long mono- 

 podially branched threads under normal conditions of growth. They are 

 largely acid fast and represent botanically a well defined group of 

 organisms, standing midway between the true bacteria and the actino- 

 myces group, which should be already more properly classified with 

 the fungi. A number of these organisms were isolated from manure 53 

 and from soil. 5455 A selective development of these organisms will 

 take place upon agar plates, containing the necessary minerals, an 



49 Ambroz, A. Dinilrobacterium thermophilum spec, nova, ein Beitrag zur 

 Biologie der thermophilen Bakterien. Centrbl. Bakt. II, 37: 3-16. 1913. 



60 Koch, A., and Hoffmann, C. Uber die Verschiedenheit der Temperaturan- 

 spruche thermophiler Bakterien im Boden und in kunstlichen Nahrsubstraten. 

 Centrbl. Bakt. II, 31: 433^36. 1911. 



51 Krohn, V. Studien liber thermophile Schizomyceten. Ann. Acad. Sci. 

 Fennicae, Ser. A. 21: 1-125. 1923. Helsingfors. 



52 Bergey, D. H. Thermophilic bacteria. Jour. Bact. 4: 301-306. 1919. 



63 Moeller, A. Ein neuer saure- und alkoholfester Bacillus aus der Tuberkel- 

 bacillengruppe, welcher echte Verzweigungsformen bildet. Centrbl. Bakt. 25: 

 369-373. 1899. 



" Sohngen, 1913 (p. 204). 



" Vierling, K. Morphologische und physiologische Untersuchungen uber 

 bodenbewohnende Mykobakterien. Diss. Univ. Heidelberg. 1921. 



