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THE ACTIXOMYCETES, Vol. I 



celium. According to Krassilnikov (1938) the 

 scant aerial mycelium of the first group is 

 devoid of branches and spirals and divides 

 into sharp-ended cylindrical cells. Reference 

 has already been made to the recent obser- 

 \'ations of Gordon and Mihm (1958) on the 

 sporulation of N. asleroides in a manner sim- 

 ilar to that of streptomyces. 



Jensen (1931) described filamentous and 

 short-celled forms of the saprophytic A^. 

 polychromogcnes, as pointed out in Chapter 

 (). Umbreit (1939) also distinguished several 

 distinct types among the nocardias : a-forms 

 with short unstable mycelium, soft colonies, 

 and diffuse growth in broth; (8-forms with 

 long stable mycelium, firm streptomyces-like 

 growth on agar, and colony type of growth 

 in liquid media, which remains clear. Um- 

 breit considered the growth in broth a more 

 definitive characteristic than any other, al- 

 though he remarked that "borderline cases 

 exist in which the investigator must resort to 

 other characteristics." Jensen suggested di- 

 vision of the genus Nocardia into two genera, 

 reserving the last name for the /5-forms and 

 retaining the name Proactinomyces for the 

 a-forms, but he added that these names 

 could probably with equal right be used for 

 the potentially acid-fast and the nonacid- 

 fast strains, respectively. A horizontal di- 

 vision (j3-forms = Nocardia, a-forms = 

 Proactinomyces) would give considerable 

 morphological homogeneity, except in re- 

 spect to motility, but would entail much 

 heterogeneity in respect to potential acid- 

 fastness and the correlated characters of 

 carbon metabolism and proteolytic power. 

 On the other hand a vertical division (acid- 

 fast = Nocardia, nonacid-fast = Proactino- 

 myces) would result in greater biochemical 

 homogeneity but a corresponding morpho- 

 logical heterogeneity. The relationship of 

 these nocadial forms to the bacteria, on the 

 one hand, and to the streptomyces and 

 micromonospora on the other, is brought out 

 in Table 15. 



]\IcClang (1949) observed that if fragmen- 

 tation follows xevy shortly after germina- 

 tion, branching will be sparse and very little 

 mycelium will be developed. With a delay in 

 fragmentation, there is opportunity for re- 

 peated branching; a larger or smaller my- 

 celium may result, according to the rate of 

 growth and the amount of subseciuent cell 

 division. The time of branching and fragmen- 

 tation in a gi\'en strain was relatively con- 

 stant under controlled conditions. 



McClung divided the n .cardia group into 

 three subgroups : 



I. Scant mycelial development, sparse branch- 

 ing, and type 1 fragmentation. Colonial tex- 

 ture soft, pasty and sometimes mucoid, pig- 

 ment intracellular and insoluble. 

 II. E.xtensive mycelial development, straight 

 branches which do not overlap, and type 3 

 fragmentation. Colonial texture soft and 

 pasty, pigment intracellular and insoluble. 

 III. Extensive mj'celial development, no frag- 

 mentation of hyphae, contorted and profuselj' 

 produced branches which overlap. Colonial 

 texture waxy or cartilaginous. (Jenerally both 

 intracellular and solul)Ie pigments are pro- 

 duced. 



JMorris describes as follows the life cycle 

 oi Nocardia: At first, a microcyst is formed, 

 which germinates on budding. The bud 

 gives rise to a long multinucleate filament, 

 which divides into individual cells by the 

 formation of transverse cell walls. The cells 

 multiply by simple fission, by complex vege- 

 tative reproduction, and by branching. No 

 prolonged diploid phase, similar to that of 

 actinomyces, is produced. Heat -fixed gram- 

 stained preparations of nocardia and actino- 

 myces may resemble each other, but cyto- 

 logically they are mark(Hlly different. The 

 conclusion was reached that there can be no 

 doubt that the aerobic nocardia constitutes a 

 separate genus from the anaerobic actino- 

 myces. The germination of the microcyst of 

 nocardia ])y ])udding is compai'able to that 

 of the spore in streptomyces, in micromono- 

 spora, and in actinomyces, but is different 



