32 MISCELLANEOUS PUBLICATION 955, U.S. DEPT. OF AGRICULTURE 



To identify an unknown micro-organism, the following procedure 

 is given. First, at the time of isolation or collection, keep as complete 

 a record as possible. Too often one thinks he will remember the cir- 

 cumstances when he first sees the organism, but later he cannot recall 

 accurately the information he needs. If the organism is going to be 

 studied in a living condition and not as a herbarium specimen for only 

 taxonomical purposes, the source of the isolate should be recorded 

 immediately. This record should include the location of the material 

 from which the isolate was made, for example soil sample, 1 inch below 

 soil surface, oak woods, Bradley Park, Peoria, 111. The data should 

 indicate whether the soil was dry or moist, the exact collection and 

 isolation dates, the medium used for isolation, and the temperature of 

 incubation. It is often well to give a brief description of the organism 

 at the time it was isolated, and if possible to photograph it. 



Sometimes organisms will change greatly after a period of time in 

 culture or be changed in the absence of other micro-organisms. With 

 organisms that have a complex morphology, such as lichens and many 

 fungi, the original plate or specimen should be dried and kept as 

 reference material. Often identification may be impossible unless this 

 is done. The isolation record should also show who collected the 

 material and who made the isolation. If the organism occurs as a 

 parasite or in association with another organism, the host should be \ 

 identified, and if this is not possible, the entire host, for instance a , 

 plant, should be collected for a plant taxonomist to identify. Any 

 unusual observation at the time of collection should be noted; for 

 example, if the organisms sporulated only in the region of growth next 

 to a certain bacterium. At this time the culture should be assigned a 

 number for record keeping. 



Before making a complete study of the isolate for purposes of iden- 

 tification, one should make absolutely certain that the culture has been 

 purified of other micro-organisms. If this is not possible, one should 

 at least know what the other associated micro-organisms were. For 

 example, in studying the genus Syncephalis, a fungus that is an obli- 

 gate parasite, it should be transferred onto a previously identified host. 

 In some cases with protozoa and algae, the culture may still contain 

 many species of bacteria. 



In the ARS Culture Collection, regardless of the source of the 

 material, we check the purity of the culture by isolating single spores 

 or cells, or if none are produced, then hyphal tips from the margin of 

 the colony. This procedure is followed whether the culture came to 

 us from an untrained person or from a laboratory with the highest 

 standards of pure-culture techniques. For Mucorales, in addition to 

 selecting spores from a single aerially borne sporophore, we always 

 inoculate the purified culture on four different media, including one 

 that almost completely suppresses growth. This procedure will allow 

 a contaminant, especially bacteria, to appear that would not ordinarily 

 be detected on the customary media used to identify the organism. 



We shall assume that by now the micro-organism has been isolated 

 in pure culture and that one knows to which of the major groups it 

 belongs. Let us assume that it is a fungus. One first examines the 

 culture and determines that it produces abundant mycelia with no 

 cross walls and that it produces spores inside saclike structures. Fur- 



