Chapter V — 89 — Metabolism 



inated only about one-third as readily as J-alanine. Leucine, isoleucine, 

 and certain other amino acids were not deaminated at all or only in mere 

 traces. 



Utilization of comflex organic coinfounds.—\t has thus been estab- 

 lished that actinomycetes are able to utilize a great variety of organic 

 compounds as sources of both carbon and nitrogen. The nature of the 

 nutrient influences not only growth of the organism, but also its cultural 

 and physiological properties, such as pigmentation, as shown in Table 

 II. Unfortunately, no satisfactory methods have been developed for 

 measuring accurately some of the changes brought about in the decom- 

 position of complex compounds, such as lignins and humus. 



Actinomycetes are able to attack numerous other complex organic 

 compounds, such as salicylaldehyde (152), paraffin hydrocarbons (113, 

 521), rubber (405), and chitinous substances (398). 



Reduction of nitrates.— Niany actinomycetes possess the capacity of 

 reducing nitrates to nitrites. The importance of this process in the nu- 

 trition of the organisms has not been fully established, although a defi- 

 nite parallelism has been observed between growth of the organisms 

 and accumulation of nitrite in the medium. It has also been estab- 

 lished that nitrite can be utilized as a source of nitrogen by many actino- 

 mycetes, provided its concentration in the medium is not high enough 

 to make it toxic (443, 444). 



Nitrate is never reduced to atmospheric nitrogen or to ammonia. 

 Wherever these products have been reported, their formation was due 

 to secondary reactions rather than to direct reduction of the nitrate. 

 Gaseous nitrogen can be formed by interaction of nitrite and amino 

 acids in an acid medium (2NOo- -f 4NHo -> 3N2 + 4HoO), a 

 combination quite unlikely in cultures of actinomycetes. Ammonia 

 can be produced in a culture containing nitrate when the synthesized 

 cell material undergoes autolysis. 



Influence of environment on growth of actincnnycetes.— It is com- 

 monly assumed that actinomycetes prefer a neutral or slightly alkaline 

 reaction for their growth, and that they are especially sensitive to a high 

 acidity; many species are not able to grow at pH 4.8 (136, 445), as 

 brought out in Table 15. The inability of most actinomycetes to grow 

 under acid conditions has been used to advantage in the control of cer- 

 tain plant diseases in the soil, especially potato scab. 



The optimum temperature for growth of most of the actinomycetes 

 usually falls between 23° and 37 °C. Certain actinomycetes are able 

 to grow at temperatures lower than 20 °C. Some organisms prefer 

 temperatures of 20° to 23 °C. Still others are thermophilic in nature 

 and are able to grow at 50° to 65 °C. The more common forms, how- 

 ever, are readily destroved at the higher temperatures, the resistance of 

 the spores being onlv slightly greater than that of the mycelium. When 

 a pulture is kept for 10 minutes at 70° C, not only the mycelium but 

 even the spores lose their viability. 



