300 PRINCIPLES OF SOIL MICROBIOLOGY 



Low temperatures (even 8° to 10°C.) do not injure the majority of 

 actinomyces. 27 High temperatures are very injurious. Some species 

 are killed at 45°. 39 The thermal death point of most actinomyces is 75°. 

 The mycelium of some organisms may survive at 60°, but is killed in 

 20 minutes at 70°; the spores may survive 75° for 20 minutes but are 

 killed in 30 minutes. Some soil organisms maybe able to withstand even 

 somewhat higher temperatures. 



The actinomyces spores resemble in this respect the spores of other 

 fungi in that they do not possess the degree of resistance of the bacterial 

 spores and are readily destroyed at temperatures a few degrees (about 5°) 

 above the destructive temperature of the mycelium. Some species are 

 thermophilic in nature and have their optimum at much higher tempera- 

 ture than the majority of actinomyces. The existence of actinomyces 

 in the soil which can grow readily at 60° is established. 40 - 41 These forms 

 are especially abundant in the upper layers of forest and garden soils; 

 they are also found abundantly in dry peat, grass, hay and straw. The 

 thermophilic forms do not represent one species, but several distinctly 

 different forms. Various investigators 42 ' 43 suggested that in the self- 

 heating of straw and other plant materials, the thermophilic forms have 

 a chance to develop and that the addition of straw or manure to the soil 

 helps to spread the organisms. The thermophilic actinomyces multiply 

 rapidly in the soil when the soil is warmed during the hot summer months 

 by the direct rays of the sun. The fact that they are found in cold 

 places where the minimum temperature (40°) for growth of thermophilic 

 forms is never reached, such as forest soils, deep subsoils, and frozen 

 soil, led Lieske to conclude that some of the common forms give out 

 mutants which develop at the higher temperatures. This whole sub- 

 ject deserves careful study. 



All actinomyces are very resistant to drying, as indicated by the 

 fact that they are found abundantly on dry straw, hay and soil. Bere- 

 stneff 44 inoculated some ears of grain with a pure culture of A. violaceus 



39 Foulerton, A. G. R., and Jones, C. B. On the general characteristics and 

 pathogenic action of the genus streptothrix. Trans. Path. Soc. London, 53: 

 56-127. 1902. 



40 Globig. Uber Bakterienwachstuin bei 50-70°. Ztschr. Hyg., 3: 294. 1888. 



41 Gilbert, tiber Actinomyces thermophilics und andere Aktinomyceten. 

 Ztschr. Hyg., 47: 383-406. 1904. 



42 Miehe, H. Die Selbsterhitzung des Heus. G. Fischer. Jena. 1907. 



43 Noack, K. Beitriige zur Biologie der thermophilen Organismen. Jahrb. 

 wiss. Bot., 51: 593-648. 1912. 



44 Berestneff, N. M. Uber die Lebensfahigkeit der Sporen von Strahlenpilzen. 

 Centrbl. Bakt. I, Ref., 40: 298. 1907. 



