CHAPTER 6 



ACTINOMYCETES AS ANTAGONISTS 



AcTiNOMYCETES are found in large numbers in many natural sub- 

 strates. They occur abundantly in soils, composts, river and lake bot- 

 toms, in dust particles, and upon plant surfaces. Certain species are 

 capable of causing serious animal and plant diseases. 



Actinomycetes, like fungi, produce a mycelium, but they are largely 

 unicellular organisms of dimensions similar to those of bacteria. Some 

 of the constituent groups are closely related to the bacteria, others to 

 the fungi. On the basis of their morphology, the order Actinomycetales 

 has been divided into three families, Mycobacteriaceaey Actinomy- 

 cetaceaey and Streftomycetaceaey comprising the genera Mycobacte- 

 riuniy Actinomyces y NocardiUy StreftomyceSy and IVLicromonosfora. 

 These genera are represented in nature by many thousands of species, 

 of which several hundreds have been described. A few are shown in 

 Figure lO. 



Comparatively little is known of the physiology of actinomycetes. 

 Some produce certain organic acids from carbohydrates (287, 1002)^ 

 others prefer proteins and amino acids as sources of energy, many spe- 

 cies being strongly proteolytic. Some are able to attack starch, with the 

 production of dextrins and sugar, accompanied by the formation of 

 diastatic enzymes. Many reduce nitrates to nitrites. Some attack sucrose 

 and form the enzyme invertasej others, however, do not. Certain spe- 

 cies are able to utilize such resistant compounds as rubber and lignin. 

 Synthetic media are favorable for the production of a characteristic 

 growth and pigmentation. Among the pigments, the melanins have re- 

 ceived particular attention. They range from the characteristic brown 

 to various shades of black and deep green and are formed in protein- 

 containing and in some cases also in protein-free media. The other pig- 

 ments range from blue, yellow, and orange to various shades of grey. 



According to Beijerinck (43), the process of pigment production by 

 actinomycetes in gelatin media is associated with the formation of a 

 quinone, which turns brown at an alkaline reaction and in the presence 

 of oxygen. The action of quinone in the presence of iron was found to 



