I'HVSIOI.OCV 



135 



whoivas the oi'ininal upp(>r l<MU|>(Matiii(' 

 limit for this culture was 12"^ ('. 



Further studies on the elTeet of lenipeia- 

 turo and humidity upon the growth and 

 death-rate of spores and mycelium of \aiious 

 streptomyces ha\-e been made hy .la^now 

 (1057). 



Amouii; the actinomycet(\s, a special u;roup 

 stands out in relation to temperatui'e condi- 

 tions. These are the thermophilic actiuo- 

 mj^cetes that are eapal)le of growing at 

 temperatures of ")() to 65° C. These or- 

 ganisms occur abundantly in manure com- 

 posts, in lieaps of hay, and in pasteurized 

 cheese. 



Cdlhert isolated several thermophilic 

 forms from various soils and included them 

 in one speci(\s, .1. tlu rniophilus. The oi)ti- 

 nuun temperature for growth was o')°, with 

 a maximum at ()()° C Most strains ceased to 

 grow at 45°, although some could be adapted 

 to grow on agai' media at 37° and even lower 

 temperatures. Clelatin was slowly liquefied. 

 Miehe looked ui)on the thermophilic actino- 

 mycetes as the characteristic organisms in- 

 habiting the decomposing masses of plant 

 material under high-temperature conditions. 

 The aetinomycete spores lost their vitality 

 rapidly, especially on agar media, but sur- 

 vived on hay particles. One organism, desig- 

 nated as A. thcrmophihis Berestnew, grew 

 well at 40 to 50° C', more slowly at :]0°, and 

 not at all at 25 and 60° C. The manner of 

 spore formation of this organism suggests 

 that it was a member of the Micromono- 

 spora group. Schiitze reported the presence 

 in decomposing clo\er hay of representatives 

 of two types of therm()j)hilic actinomyeetes, 

 one of which was designated as ,1. thenno- 

 philus Berestnew and the other as .4. 

 monosporus Lehmann and Schiitze. The 

 latter may also be considered a memfjer of 

 the Micromonospora type. 



Further studies on the germination of 

 heat-resistant spores of M . vulgaris led l''.rik- 

 son (1955a) to conclude that heat actixation 



at lOO'^C foi- I minute enhanced the initial 

 g(>rmination rate of the s|)ores within the 

 lirsl ;;-honr period. When the spoics ha\-e 

 been subjecled to temp<'rat ures of 1()()°(' for 

 more than 1 hour, sectored colonies showing 

 loss of aerial mycelium and impaired viabil- 

 ity fre(|uently developed. iM'ikson (l()55b) 

 further leported that a pathogenic partially 

 acid-fast culture of A'', sebivorans and a 

 closely allied form were capable of with- 

 standing exposure to 90°C for 10 minutes 

 when dispersed in phosphate buffer suspen- 

 sion. Subjection to heat treatment (90°C for 

 1 minute) of a blood culture belonging to the 

 S. albiis group increased the autolytic 

 tendency of the culture and affected the t3^pe 

 of sporophore produced during the first 

 generation. 



Waksman, Gordon, and Hulpoi made a 

 study of the occurrence of actinomj-cetes 

 in high-temperature composts, as will be 

 shown in Chapter 16. Waksman and Corke 

 examined the classification of the thermo- 

 philic actinomyeetes and came to the con- 

 clusion that these microbes i-epresent two 

 distinct groups of the Streptomyces and 

 Thermoactinomyces types. Temperature- 

 growth relationships of Micromonospora 

 ha\-e been studied in detail by Erikson and 

 Webley. 



Effect of Drying 



Alicrobes vary greatly in their sensiti\-ity 

 to drying. Some are highly sensitive and 

 cannot I'esist drying more than a few min- 

 utes or a few hours; others remain ali\'e for 

 many years. The composition of the me- 

 dium is of great importance in this connec- 

 tion; the presence of protein in the medium 

 greatly increases the period of resistance to 

 drying. Bacteria remain ali\'e in normal air 

 for a much shorter time than in dry air, 

 because of the moisture content of the 

 former. In dry air, many bacteria remain 

 alixc foi' years. Bacterial spores resist drying 

 nnich more I'cadily and for a longei- period 



