Chapter 11 



Thermophilic Actinomycetes 



Our knowledge of the thermophilic actino- 

 mycetes dates back to the early beginnings 

 of general microbiology. The first students 

 of the microbiological population of soils and 

 composts observed that some of the organ- 

 isms found among the bacteria, actinomy- 

 cetes, and fungi were able to grow at much 

 higher temperatures than the great majority 

 of the members of these groups. 



Globig (1888) was the first to isolate from 

 the soil thermophilic actinomycetes, capable 

 of growing at 52-o5°C. Rabinowitsch (1895) 

 and Tsiklinsky (1903) isolated similar cul- 

 tures from manure, and Xoack (1912) iso- 

 lated them from hay. Numerous other iso- 

 lations of thermophilic actinomycetes were 

 made, from ordinary soil by Gilbert (1904), 

 from desert sand, feces, air, and peat, as 

 well as from human intestines and from 

 sewage. It has also been observed repeatedly 

 that composted manure, when it has attained 

 a high temperature, or hay which has been 

 allowed to heat in composts, becomes cov- 

 ered with small white patches of fungus-like 

 growth. Miehe (1907) remarked that the 

 appearance of these patches is similar to a 

 coat of lime and is due to actinomycetes. 

 Similar observations of thermophilic com- 

 posts have been made by various other in- 

 vestigators. 



Tsiklinsky inoculated potato slices with 

 soil or with manure and incubated them at 

 53-55°C. Isolations were made on agar 

 plates after l(i hours. Two cultures were 

 thus obtained. One produced chains of spores 

 and was considered to be, therefore, a true 

 actinomycete of the type now designated as 



Streptomyces. The other formed round or 

 ovoid spores at the end of side branches, by 

 the swelling of the tips. This organism was 

 believed to be widely distributed in nature 

 and was named Thermoactinomyces vulgaris- 

 Because of its manner of spore formation, 

 this form was believed to belong to the group 

 of actinomycetes designated by 0rskov 

 (1923) as Micromonospora, and was, there- 

 tore, classified by Waksman as Micromono- 

 spora vulgaris. It grew at 48-68°C, with an 

 optimum at 57°C, and no growth at 70°C. It 

 remained inert for a month at 'A7°C or at 

 lower temperatures, but it became active 

 within 24 hours at 56-57°C. The spores were 

 said not to be destroyed at 100°C, even after 

 20 minutes. The organism grew readily on 

 most ordinary media; it was proteolytic but 

 not amylolytic. The Streptomyces, on the 

 other hand, was weakly proteolytic, and the 

 spores were less resistant to heat (Fig. 58). 



Gilbert cultivated from various soils 

 several strains of a thermophilic actino- 

 mycete, which he designated as A. thermo- 

 philics. Growth on potato was much folded, 

 white, later becoming gray on the surface; 

 the plug" was darkened by some cultures. 

 The optimum temperature was 55°C; no 

 growth took place at 60°C. Most sir: 'ins 

 ceased to grow at 45°C, whereas some could 

 be adapted to grow on agar media at 'A7°C 

 and even at 22°( 1 . The colonies on agar were, 

 after 24 to 48 hours, small, folded, light 

 yellow with a dark-colored center. Gelatin 

 was only slowly liquefied. 



Miehe considered hot composts and not 

 soils as the natural substrates of actino- 



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