^r()l{PIl(>l,(>(;^ , (•^'|■()l.(>(;^ , and i.iki". cvcj.ks 



93 



iuy('(Mi>s. ()i-sk()\- :m(l ollicrs Ix-licxcd ili;it 

 t\)nuatioii of si^pta is ihc lirsl staj^c in ihc 

 process ol' tlu- hrcak-iip oi' ilu> mycelium 

 into fnigmciils. 



Cortain swellings of the terminal ends of 

 hyphae may he obserxed in old cultures. 

 They are also foriiKMl uiuUm- al)normaI urow 1 li 

 conditions, as in conc(>ntrateti media oi' in 

 tlu> presence of certain specific sul)stances 

 like catTeine. These swellings may he con- 

 sidered as involution forms, somewhat simi- 

 lar to the cluhs produced by pathogenic 

 actinomycetes in the animal bod3\ 



Further information on the morphology 

 of the streptomyces group is found in the 

 work of Ivnaysi, McGregor, Penau vt ai, and 

 Prokofieva et al. The degeneration of strep- 

 tomyces was analyzed hy Williams and 

 j\fcCoy (1953). See also studies hy l^isset 

 (1957). 



Micromonospora 



Members of the genus Micromonospora 

 are characterized by the formation of a well- 

 developed branching vegetative mycelium, 

 similar to that of Streptomijces. Single spheri- 

 cal to oval spores are produced on the tip 

 of special sporophores or side branches of 

 the vegetati^'e mycelium. No surface growth 

 is formed in lif[uid media. When such media 

 are stirred or continuously shaken, thus 

 resulting in the breaking up of the spores, an 

 abundance of new clumps or colonies are 

 produced. Aerial mycelium, if formed at all, 

 is of the nocardial type, consisting of fila- 

 ments mostly unhranched and undivided. 

 Micromonosporas have frequently been 

 looked upon as the most highly developed 

 group of actinomycetes, closest to the fungi. 



Erikson (1953) described M. chalccac as 

 producing a slowly de\'eloping mycelium of 

 \ery slender, profusely branched filaments, 

 liearing single spores on short lateral 

 branches. There is no aerial mycelium; in 

 instances where it has been reported, it is 

 sparse, infreriuent, and rex'ei'sihle. TJiis in- 



\('st igaloi' emphasized the profound physio- 

 logical dil'fei'ences between the mesophilic 

 micromonosporas which can utilize cellulose, 

 chit in, htinin, and other I'esistant com- 

 pounds, and tile lheiinoi)liilic forms, which 

 cannot (Mrikson, i'.)H, 1!).")2). The thermo- 

 philic M. ruhioris was said to exhibit con- 

 sistently- a pattern of mycelial de\-elopment 

 which differs umnistakably from that of the 

 mesopliilic M . fusnt. Pigment was not pro- 

 duced by the thermophilic species. 



According to Erikson (1953), the most 

 characteristic morphological properties of 

 the thermophilic ]\f. vulf/aris is that it forms 

 at ()0°C an abundant white felt of aerial my- 

 celium. The filaments of the secondary aerial 

 mycelium bear single, highly refract ile spores 

 on short lateral branches, in the same man- 

 ner as do the vegetative filaments of the 

 primary mycelium. Since only sparse de- 

 \elopment of aerial mycelium takes place at 

 37°, this secondary aerial growth was re- 

 garded as an expression of thermal dimor- 

 phism. It plays an important part in the life 

 of the organism, as indicated by the high 

 oxygen uptake by the aerial mycelium at G0°, 

 as compared with the very low \alues given 

 by the primary vegetative growth. 



The aerial mycelium of il/. vulgaris seg- 

 ments rapidly to form elongated branching 

 chains of short cells which "bud," producing 

 spores on Yciy short stalks. The ^'egetati^'e 

 mycelium continues to show undifferentiated 

 filaments which sooner or later disintegrate, 

 thus showing a much lower degree of via- 

 bility. These properties also can be demon- 

 strated in the mesophilic micromonosporas. 

 Very little vegetative growth of M. vulgaris 

 is producc^l on artificial media and in its 

 natural hal)itat. There the proportion of 

 aerial mycelium and spores is visibly much 

 higher. These results tend to sui)port the 

 decision made l)y Henssen and in this treatise 

 to separate the thermophilic and mesophilic 

 forms into dilTei-ent genera. 



