ACTINOMYCETES AS ANTAGONISTS 103 



be similar to that of the enzyme tyrosinase. Since an excess of oxygen is 

 required for the formation of quinone, only limited amounts are found 

 in deep cultures. The quinone is believed to be formed from the pep- 

 tone in the medium j although good growth was produced on media 

 containing asparagine, KNO;., and ammonium sulfate as sources of ni- 

 trogen, only traces of quinone, if any, were found. The tyrosinase reac- 

 tion is not involved in the production of all black pigments by actinomy- 

 cetes (945) i some species produce such pigments in purely synthetic 

 media, in the complete absence of peptone. 



Actinomycetes grow in liquid media in the form of flakes or small 

 colonies, usually distributed either on the bottom and walls of the con- 

 tainer or throughout the liquid j often a ring is formed on the surface 

 of the medium around the wall of the vessel. In many cases, a full sur- 

 face pellicle is produced, which may be covered with aerial mycelium. 

 As a rule, the liquid medium does not become turbid, even in the pres- 

 ence of abundant growth. When grown on solid media, actinomycetes 

 form small, compact, soft to leathery colonies j a heavy lichen-shaped 

 mat is produced that may become covered by an aerial mycelium. The 

 addition of a small amount of agar (0.25 per cent) to a liquid medium is 

 highly favorable to growth, especially in large stationary containers. 



Actinomycetes can also be grown in liquid media in a submerged con- 

 dition, with suitable agitation and aeration in order to supply oxygen j 

 the medium may also be kept in shaken state (287, 926, lOOi, 1002). 

 Growth occurs in the form of a homogeneous suspension of discrete 

 colonies and mycelial fragments throughout the liquid. Responses in 

 growth and biochemical activities as a result of treatments may thus be 

 obtained under more homogeneous physiological conditions. 



Although most actinomycetes are aerobic, some are anaerobic, and 

 many can grow at a reduced oxygen tension. The aerobic actinomycetes 

 commonly found on grasses and in soil are said (490) never to have 

 been isolated from animal infections. Mixed infections consisting of 

 anaerobes growing at body temperature together with aerobes have 

 often been demonstrated. Certain aerobic species also are capable of 

 causing infections in man and other animals, and certain plant diseases 

 (potato scab, sweet potato pox) are caused by aerobic species of actino- 

 mycetes. 



