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THE ACTINOMYCETES, Vol. II 



idly; when these tests were repeated three 

 times, considerable variation in the degree 

 of liquefaction was obtained. Kutzner (1956) 

 kept gelatin cultures for 31 days; only four of 

 210 failed to liquefy the gelatin. Reports of 

 inability to liquefy gelatin or coagulate or 

 peptonize milk of certain species may often 

 be questioned. Repeated tests with different 

 inocula might have shown different results. 

 Gordon and Smith (1955) suggested casein 

 hydrolysis as one criterion for the separation 

 of Streptomyces strains from those of Nocar- 

 dia. 



Stapp (1953) reported further that in his 

 collection 18 cultures brought about coagula- 

 tion of milk without subsequent peptoniza- 

 tion, 431 caused coagulation and peptoniza- 

 tion, and 19 caused peptonization without 

 previous coagulation. A few cultures occa- 

 sionally are found that cause no coagulation 

 or peptonization. One wonders whether re- 

 peated tests with different inocula might 

 show different results. 



REDUCING PROPERTIES 



The reduction of nitrate to nitrite has 

 been universally used among the criteria for 

 species differentiation. In view, however, of 

 the influence of nutritional factors upon this 

 reaction, and its quantitative rather than 

 qualitative nature, its significance in species 

 characterization may be questioned. 



Proteolysis, starch hydrolysis, sucrose in- 

 version, cellulose utilization, and nitrate re- 

 duction were said (Krassilnikov, I960) to be 

 characteristic of almost all actinomycetes 

 and to have, therefore, no taxonomic signifi- 

 cance. Sugar assimilation was considered, 

 however, as a more or less constant property. 



UTILIZATION OF NITROGEN SOURCES 



As a rule, utilization of nitrogenous com- 

 pounds has not been considered important 

 for species characterization. Shinobu (1958) 

 considered the utilization of urea, creatinine, 

 and certain amino acids as of some impor- 



tance in species characterization. Gordon 

 and Mihm (1959) suggested that the ability 

 to attack casein, tyrosine, or xanthine can 

 be considered of some significance in charac- 

 terizing species. 



The use of hydrogen sulfide production as 

 a taxonomic implementation in the differen- 

 tiation of Streptomyces specie* has been sug- 

 gested by Pridham (1948). Tresner and 

 Danga (1958) later modified the peptone- 

 iron agar medium. More than 900 strains 

 belonging to one or another of 94 species 

 were tested. There was a marked difference 

 in response from strain to strain within a 

 species; for example, 98 per cent of 227 

 strains of S. hygroscopicus were negative; 99 

 per cent of 112 isolates of S. lavendulae were 

 positive. When employed in conjunction 

 with other physiological, cultural, and mor- 

 phological criteria, hydrogen sulfide produc- 

 tion was said to give promise as an aid in 

 the systematics of the genus Streptomyces. 



Sensitivity to Antibiotics 



Actinomycetes, especially species of Strep- 

 tomyces, have been found in recent years to 

 produce a series of highly valuable chemical 

 substances, notably, antibiotics. This prop- 

 erty has come to be considered as highly 

 characteristic of a given species. The fact 

 that a large proportion of all the cultures of 

 Streptomyces isolated from natural sub- 

 strates show some degree of inhibition of 

 growth of other microorganisms, when tested 

 on suitable media, suggested the ability to 

 form antibiotics to be of potential diagnostic 

 value. It is a question whether one is a 

 "lumper" or a "splitter" when one regards 

 the ability to produce an antibiotic as a 

 species rather than a strain characteristic. 

 Certain antagonistic strains belonging to the 

 S. griseus group, for example, are able to 

 produce various streptomycins and cyclo- 

 heximide. Others may form various actino- 

 mycins, grisein, streptocin, or candicidin. 



It has been suggested that because the 



