C li A l» I i: l{ 2 



Isolation, Identification, Cultivation, 

 and Preservation 



Most of the techniques used in the isola- 

 tion and cultivation of bacteria and fun^i 

 also apply to actinomvcetes. The isolation 

 of these organisms from soils and other nat- 

 ural substrates is brought about by first 

 plating out such materials in proper dilu- 

 tions on suital)le agar or gelatin media. The 

 plates are incubated at favorable tempera- 

 ures, for 2 to 7 days, and the colonies* 

 picked and transferred to sterile litjuid or 

 solid media for further development. When 

 the culture is found to be contaminated with 

 other organisms, a second plating may ha\'e 

 to be resorted to, to obtain pure cultures. 



Actinomycete colonies can easily be dis- 

 tinguished on the plate from those of fungi, 

 on the one hand, and of true bacteria, on the 

 other. They are compact, often leathery, 

 giving a conical appearance, and have a dr}" 

 surface. They are often covered with aerial 

 mycelium. If the colony is well developed 

 and the aerial mycelium abundant, the sur- 

 face spores can easily be picked with a sterile 

 needle. If growth is limited, or the aei'ial 

 mycelium not fully developed, sharp, razor- 

 like needles are recjuired to transfer a part 

 of the growth to fresh media. 



When grown in liquid culture, either in a 

 stationary or in a submerged condition, the 



* A colony of an actinomycete is different from 

 a bacterial colony. It represents a filamentous 

 extension of the original cell or cells, spores, and 

 degradation products; it is not an accumulation 

 of cells originating from one or more similar cells. 



majority of actinomycetes, notably members 

 of the genera Streptomyces and Micromono- 

 spora, grow in the form of flakes or spherical 

 compact masses, leaving the medium clear. 

 The mass of growth can easily be remo\-ed 

 by filtration through ordinary paper. Only 

 when growth undergoes lysis do the cells 

 disintegrate completely and a certain degree 

 of turbidity occurs. 



Method of Study 



In view of the ability of actinomycetes to 

 produce both substrate or vegetati\-e growth 

 and aerial mycelium that usually forms spe- 

 cial reproducti\'e cells, known as spores or 

 conidia, it is natural that these organisms 

 should be found in nature both in the form 

 of hyphae or masses of more complex myce- 

 lium and as spores. The presence of hyphae 

 or mycelium in the soil or in other materials 

 is usually considered as evidence that actino- 

 mycetes lead in such substrates an autoch- 

 thonous or natural existence and that they 

 form a part of the nati\-e microbial popula- 

 tion. The presence of spores alone, without 

 mycelium, may suggest that actinomycetes 

 ha\'e been introduced there by air or by wa- 

 ter. 



The methods of studying the actinomycete 

 population of soil, water, compost, and other 

 materials are similar to those used in the 

 study of most of the bacteria and fungi. 

 These methods include: (a) microscopic ob- 



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