30 



THE ACTINOMYCETES, Vol. I 



they live and multiply; other substrates 

 represent only temporary habitats for ac- 

 tinomycetes, where they are distributed by 

 water and air movements. They are also 

 found in the far north and on high moun- 

 tains, in deep layers of soil, and in oil de- 

 posits. Some genera favor one habitat and 

 others favor another. Strcptomyces is most 

 commonly represented in soils and in com- 

 posts; Micromonospora species are abundant 

 in lake bottoms ; some members of the genera 

 Actinomyces and Nocardia are known to be 

 causative agents of human and animal dis- 

 eases; Thermoactinomyces and other ther- 

 mophilic genera grow abundantly in stable 

 manure and in high-temperature composts. 

 Enghusen (1956) explained the wide distri- 

 bution of Strcptomyces species by the small 

 size of their spore (1.0-1.5 by 0.5-0.8 ix) and 

 by their resistance to drying (for 3 years or 

 more) . 



On the basis of their actinomycete popu- 

 lations, from both a quantitative and a fiiial- 

 itative point of view, the following natural 

 substrates may be recognized: 



1 . Soils, comprising virgin and cultivated, 

 garden, field, and forest soils, as well as 

 drained peat bogs. 



2. Sea waters and sea bottoms. 



3. Fresh water basins, comprising lake 

 and river waters and bottoms. 



4. Manures and composts. 



5. The atmosphere. 



6. Food products, including milk. 



7. The bodies of plants: some find in and 

 upon the plant a temporary or permanent 

 habitat; others are able to cause diseases of 

 plants. 



8. The bodies of man and animals, espe- 

 cially the digestive system. 



9. Geological formations. 



Occurrence and Al)un<lance of Actino- 

 mycetes in the Soil 



The distribution of actinomycetes in \ari- 

 ous soil types began to receive attention soon 



after the recognition of their existence as a 

 separate group of microorganisms. The exact 

 enumeration of the large numbers of species 

 found in the soil was actually begun, how- 

 ever, during the first years of this century. 



For a time after the first designation and 

 description of an actinomycete by Cohn, but 

 little attention was paid to the occurrence of 

 actinomycetes in nature, aside from the ani- 

 mal pathogens. Globig was among the first 

 to draw attention, in 1888, to the occurrence 

 of actinomycetes in the soil. He isolated a 

 thermophilic organism, using potato as a 

 medium. Another form was soon isolated 

 from the air by Rossi-Doria (1891) and des- 

 ignated Streptothrix alba. In 1900, Beijerinck 

 established that actinomycetes occur in great 

 abundance in the soil. He found them in 

 garden soil at a depth of 1 m, in sandy soil 

 to a depth of 2 m; he also found them in the 

 bottom mud of a river bed. Beijerinck em- 

 phasized that actinomycetes are omnivorous 

 organisms, living and growing under a great 

 variet^y of conditions. 



The first quantitative enumeration of 

 actinomycetes in the soil was made by Hilt- 

 ner and Stormer, in 1903. The gelatin plate 

 method was used. The numbers of actino- 

 mycetes were found to A'ary between 13 and 

 30 per cent of the total microbial flora of 

 the soil capable of developing on the plate. 

 These variations depended primarily on the 

 season of year; from 20 per cent in the spring, 

 they dropped to 13 per cent in summer, and 

 rose to 30 per cent in the fall. The last in- 

 crease was ascriV)ed to the addition of fresh 

 undecomposed plant and animal residues. 

 The introduction of stable manure into soil 

 also had a marked effect in increasing the 

 number of actinomycetes. 



Fischer found that actinomycetes com- 

 prise 15 per cent of the microbial population 

 of sandy soils. Fousek reported that the 

 higlu^st numb(M-s of actinomycetes are found 

 in the fall of the year (27 to 35 per cent of 

 all colonic^s); the lowest numl)er occurred in 



