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 A ctinomycetales 

 has been divided into three families, Mycohactenaceae^ Actinomy- 

 cetaceae^ and Streftomycetaceaey comprising the genera Mycobacte- 

 riumy Actinomyces y Nocardiay StreftomyceSy and Micromonosfora. 

 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 i^ known of the physiology of actinomycetes. 

 Some produce certain organic acids from carbohydrates j others prefer 

 proteins and amino acids as sources of energy, many species being 

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

 of dextrins and sugar, accompanied by the formation of diastatic en- 

 zymes. Many reduce nitrates to nitrites. Some attack sucrose and form 

 the enzyme invertasej others, however, do not. Certain species 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 received par- 

 ticular 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 pigments range 

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



According to Beijerinck (41), the process of pigment production by 

 actinomycetes in gelatin media is associated with the formation of a 



