84 



THE ACTINOMYCETES, Vol. I 



that caused other strains to form aerial 

 m^'cehum. 



Secondanj Aerial JMijcelium 



Cultures with a normally gray aerial my- 

 celium may be observed to form in spots a 

 white or yellowish mycelium. When such 

 mycelium is transferred to fresh agar, cul- 

 tures are obtained that differ from the 

 mother culture only in the color of the aerial 

 mycelium but in no other property. Oc- 

 casionally, a "secondary aerial mycelium," 

 cottony in nature and white in color, is 

 produced from a powdery gray, rose, or blue 

 aerial mycelium. This is usually sterile in 

 nature, as shown, among others, by Jensen 

 (1931) and Kutzner. Cultures obtained from 

 the secondary aerial mycelium (strains) 

 are distinguished from the original cultures 

 (strains) by the color, sterility, and mor- 

 phology of the aerial hyphae. 



Coremia 



The sporulating hyphae of certain species 

 of Streptomijces may be grouped together 

 into clumps reminiscent of the typical core- 

 mia of fungi. They are formed only at cer- 

 tain spots on the surface of the colonies. 



FicrRE 43. Spiral format ion by stre])l()inyccs 

 (Reproducetl from: Baldacci, E. ct at. Cliorn. 

 Microbiol. 1: 521, 1956). 



They were first described by Lieske. The 

 aerial spores of such cultures are no different 

 from those of other cultures. Krassilnikov 

 (1938) reported the formation of coremia 

 both in the substrate and in the aerial 

 mycelium. These coremia are cylindrical or 

 cone-shaped, 1 to 2.5 mm in length, the cen- 

 tral portion being made up of vegetative 

 hyphae and the surface of aerial hyphae. 



Spore Formation 



As pointed out previously, Lachner-San- 

 doval was the first to describe, in 1898, the 

 mechanism of sporulation among the actino- 

 mycetes. The "fragmentation" spores were 

 considered to be analogous to the spores pro- 

 duced by true fungi. They are formed by the 

 breaking up of the protoplasm within the 

 cell wall into particles or fragments, more or 

 less uniform in size. These are later liberated 

 by the splitting of the cell wall. During the 

 contraction of the fragments, empty and 

 clearer partitions are formed between them, 

 which have been occasionally taken for 

 cross walls. The spore-bearing threads thus 

 assume the appearance of chains of cocci, 

 the spores falling apart readily. This manner 

 of sporulation begins at the top of the aerial 

 spore-bearing hyphae antl proceeds toward 

 the base; it is characteristic of the genus 

 Streptomyces. Recently, Cordon ;ind Mihm 

 (1958) have shown that certain strains of 

 Nocardia {N. asteroidea) ha^'e a similar mode 

 of sporulation in the aerial mycelium. 



In the "segmentation" spores, the sporu- 

 lating hyphae break up by means of cross 

 walls. At first the hyphae are imicellular. At 

 a certain stage of growth, cross walls are 

 produced and the hyphae break up into 

 small segments. These are cylindrical in 

 shape and uniform in size, usually 1 to 2.5 

 by 0.7 to 0.8 ^l. Neukirch (1902) designated 

 the segmentation spores also as "fragmenta- 

 tion spores" and described as "oidiospores" 

 another type of sporulation that appears in 

 older cultures through the break-up of the 



