136 



THE ACTINOMYCETES, Vol. I 



than do vegetative cells. The mycelium of 

 most fungi is readily destroyed on drying, 

 while the spores are killed only after pro- 

 longed drying, the period varying with the 

 species. The greater resistance of the spores 

 is due to their lower water content; the 

 mycelium of a Pcnicillium was found to con- 

 tain 87.6 per cent of water, and that of the 

 spores 38.9 per cent. 



Actinomycetes are very abundant in dry 

 soils and are, in general, markedly resistant 

 to drying. Acosta kept a culture of an actino- 

 mycete (.4. invulnerabilis) alive in a fully dry 

 state for 9 years. Berestneff inoculated a cul- 

 ture of aS. violaceus on sterile rye straw and 

 allowed it to grow until sporulated. After 

 being kept m a dry state for 10 years in the 

 laboratory, it was still alive. 



Lieske prepared dry cultures (on sterile 

 filter paper) of Streptomyces, Nocardia, and 

 Actinomyces in a desiccator, over dry CaCl2 

 and sulfuric acid. The cultures were alive 

 after 18 months. Different organisms differ 

 greatly, however, in their ability to survive 

 drying under ordinary atmospheric condi- 

 tions. 



Krassilnikov (1938) emphasized the re- 

 markable ability of actinomycetes to survive, 

 under most unfavorable conditions, for very 

 long periods. 



Influence of Light 



Actinomycetes do not need light for their 

 activities. In fact, strong light, especially 

 M^hen prolonged, has an injurious effect upon 

 their development. The effect of light de- 

 pends to a great degree upon the medium in 

 which the organisms are grown ; the cells are 

 usually more resistant in milk than are those 

 in bouillon. The resistance of the organisms 

 to light is greater in a dried than in a moist 

 condition. The injmious action of light in- 

 creases with the intensity of the source of 

 light. Sunlight acts only on the surface of 

 solid media or in the air to which the or- 

 ganisms are exposed. In liquid media, those 

 organisms which are sul)j(M'le(l to the great- 



est intensity and are only slightly protected, 

 are destroyed. 



The red and orange rays of the light 

 spectrum, as well as the infrared, or heat 

 rays, have no effect upon the growth and 

 activities of microbes. Blue and violet, and 

 especially the ultraviolet, are the most in- 

 jurious rays of the spectrum. \^arious ex- 

 planations of the mechanism of the micro- 

 bicidal action of ultraviolet radiations have 

 been offered. It is known that microbes ab- 

 sorb the lethal rays and that the proteins 

 have absorption bands between 2480 A and 

 2710 A. The effective radiation for steriliza- 

 tion is in the region of waxe lengths of 2800 

 A to 2500 A. The capsulated organisms are 

 most susceptible; the sporulating organisms 

 are most resistant. 



When a microbial culture is suddenly 

 brought to light, the protoplasm contracts 

 and a partial dehydration of the cell contents 

 takes place under the influence of the rise 

 in temperature. When the culture is returned 

 to darkness, the reverse takes place. Ultra- 

 violet radiation produces an enormous con- 

 traction; the vacuoles are reduced and may 

 even disappear, followed by plasmolysis. 



The antibacterial action of radiations, 

 comprising both the long ultraviolet ( > 3500 

 A) and short visible (<4900 A) rays, has 

 recently attracted considerable attention 

 from the point of view of destruction of un- 

 desirable organisms and development of 

 mutants from desirable ones. The region of 

 3500 to 4900 A is particularly effective. It 

 was concluded that the extended nature of 

 the killing curve suggests the production of 

 some toxic sul)stance, or the destruction of 

 some essential compound in the cell, the 

 eflect of which, up to a certain limit, does 

 not permanently destroy the ability of the 

 cell to divide and develop further. Wave 



o 



lengths shorter than ."JOOO A are most ef- 

 ficient at 2650 A, close to the wave lengths 

 at which nucleic acids act as most active 

 absorbents. The phenomenon of photoreac- 



tix'ation greatlv influ(Mi('(>s the killing effect 



