Waksman — 68 — Actinomycetes 



apart into short rods and cocci, by a process of segmentation, compar- 

 able to oidia formation. The spores germinate, giving rise to a true 

 mycehum. Some of the members of this group are characterized by a 

 marked plemorphism, being either acid-fast or non-acid-fast. The 

 angular type of growth described for some of the actinomycetes is also 

 a property of certain members of this group. In recent studies on the 

 nocardias, Erikson (1151?) examined 300 strains, freshly isolated from 

 soil or obtained from culture collections. On immediate isolation, only 

 9 per cent were partly acid-fast, but on subsequent cultivation on organic 

 matter-rich media, this increased to 31 per cent. These strains ranged 

 from those giving soft mycobacterial type of growth with transient vege- 

 tative mvcelium and very sparse aerial mvcelium to the harder strepto- 

 myces-like varieties. No evidence was obtained of any resting spores 

 or chlamydospores in the vegetative mycelium; the aerial mycelium, 

 if present, does not form any true spores. The nocardias were, there- 

 fore, considered as asporogenous. 



The genus Stre^ptomyces produces a well-developed nonseptated 

 mycelium. The vegetative mycelium does not divide during its de- 

 velopment but gives rise to a somewhat thicker aerial mycelium, which 

 is formed most readily on synthetic or poor media. The aerial hyphae 

 produce straight or curved sporulating branches. These give rise to 

 conidia, by a process frequently designated as fragmentation. The 

 spores are produced within the sporulating hyphae and are separated 

 from one another by a constriction process. Later they are liberated 

 by constriction of the cell wall and, its subsequent dissolution. The 

 process of segmentation or oidia formation may also occur among the 

 members of this genus. The substrate mycelium may produce chlamy- 

 dospores; the broken bits of mycelium also have the capacity of growing 

 into a fresh mycelium. 



The genus Microinonospora is characterized by the formation of a 

 well-developed branching mycelium, producing single oval spores on 

 the tip of special sporophores or side branches. These spore-bearing 

 branches may be single or much-branched, the latter giving rise to a 

 mass of spores similar to a bunch of grapes. No surface growth is 

 produced in liquid media, but abundant growth is formed when such 

 media are stirred or shaken at frequent intervals, thus breaking up the 

 spores, which give rise to new clumps or colonies within the media. 



Micromonosfora may be looked upon as the most highly developed 

 group among the actinomycetes, placing the whole order Actinomv- 

 cetales closest to the fungi. On the other hand, the genus Nocardia 

 is in many respects related to the mycobacteria, and, through them, to 

 the true bacteria. 



