Chapter XII 



SUMMARY 



Actinomycetes are among the most widely distributed groups of 

 microorganisms. Thev are of universal occurrence and they play an 

 active part in the cycle of life in nature. 



One of the early students of the group, Beijerinck, recognized that 

 they are omnivorous organisms and that they are capable of living both 

 in a nutrient-rich and in a very poor en\dronment. Water and air 

 were said to supply nutrients for the modest needs of these organisms. 



Actinomycetes are- able to utilize both inorganic and organic forms 

 of nitrogen. The extent of their growth upon artificial media is gov- 

 erned bv the available energy, the supply of oxygen, available nitrogen, 

 and certain other nutrient elements. One of the greatest contributions 

 to a better knowledge of these organisms was their cultivation on syn- 

 thetic media, upon which they form characteristic morphological struc- 

 tures and upon which thev develop a variety of specific biochemical 

 characteristics. 



Actinomycetes are capable of breaking down proteins to amino acids 

 and to ammonia; frequently, active proteolytic enzymes are produced. 

 They are able to utilize a large variety of organic compounds for nutri- 

 tive purposes and grow under various favorable and adverse conditions. 

 Manv actinomvcetes are strongly diastatic, and many are capable of at- 

 tacking various hemicelluloses. Some are able to utilize cellulose, some 

 attack lignins, paraffins, fats, and rubber-like materials. 



Manv actinomvcetes are able to reduce nitrate to nitrite, but not 

 to ammonia or atmospheric nitrogen. Beijerinck believed, however, 

 that under certain conditions this reduction may lead to losses of nitro- 

 gen through the interaction of nitrites with ammonium compounds. 



Actinomycetes are unable to fix atmospheric nitrogen, certain re- 

 ports to the contrary notwithstanding (32). These reports were based 

 upon the observation that many actinomyces colonies develop on media 

 to which no fixed form of nitrogen has been added. The limited 

 growth produced by such colonies can easily have obtained their nitro- 

 gen from various impurities in the medium or in the atmosphere. Ac- 

 tinomvcetes do not nitrify ammonium salts, although detection of small 

 amounts of nitrites has been reported (308) in media containing am- 

 monia; this may have been due to the sensitivity of nitrite reagents. 

 ^ Certain actinomycetes can develop at temperatures as high as 60° 



