GROUPS AND SPECIES OF GENUS STREPTOMYCES 



v; 



and that spirals also may be formed. A 

 streptomycete tonus a characteristic aerial 

 mycelium. This property may be lost, how- 

 ever, on continued cultivation or under 

 special conditions of treatment. The aerial 

 mycelium frequently develops characteristic 

 spirals, tufts (Fig. 22), or verticils (whorls). 



2. A streptomycete usually multiplies by 

 the concentration and fragmentation of the 

 protoplasm within a filamentous cell, fol- 

 lowed by the dissolution of the cell mem- 

 brane. The fragmented portions of the my- 

 celium usually develop, under favorable 

 conditions, into fresh mycelium, either by 

 germ tubes or by lateral budding. Spores or 

 conidia are produced. The substrate my- 

 celium does not segmenl spontaneously into 

 bacillary or coccoid tonus, but remains non- 

 septate and coherent even in old cultures, 

 thus forming the characteristic tough tex- 

 t ured, leathery growth. 



:!. In nocardias, the aerial hyphae are 

 believed to represent an upward extension 

 of the substrate mycelium, and usually do 

 not exhibit any differentiated protoplasm. 

 When a streptomycete loses its capacity to 

 produce aerial hyphae, a form analogous to 

 that of a nocardia may result, except for 

 the structure of the mycelium and that 

 faculty of the degenerated culture to regain 

 the lost capacity. 



4. Another difference between nocardia- 

 and streptomycetes is the acid-fastness or 

 partial acid-fastness of some of the formei 

 when grown in certain media; the latter are 

 never acid-fasl . 



As pointed out in Chapter I, Gordon and 

 Smith (l!>.V)i proposed six distinctive char- 

 acter- for the separation of the two genera. 

 These criteria are: (a) colony structure; (b) 

 casein hydrolysis; (c) dissolution of tyrosine 

 and xanthine; (d) acid production from glu- 

 cose and glycerol; (e) lack of acid formation 

 from arabinose, xylose, lactose, mannitol, 

 and inositol; and (f) utilization of acetate, 

 propionate, pyruvate, malate, and succinate. 



Strains of organisms giving positive re- 



Figure 22. Tufi formal 

 of t he Streptomyces tins* u. 



suits in five or six of the physiological tests 

 belong to Streptomyces; strains with four 

 to six negative reactions, to Nocardia. 



Although considered a- somewhat arbi- 

 trary, these criteria allowed clear-cut generic 

 separation of 07 per cent of 251 strains 

 studied, regardless of their morphological 

 variation. Nmety-six per cent of the strains 

 received as Streptomyces were positive in 

 five oi .-ix of the following reactions: hy- 

 drolysis of casein, dissolution of tyrosine, 

 and acid production from xylose, mannose, 

 maltose, and lactose. Strains that no longer 

 formed aerial hyphae and spores, but known 

 to be descendants of typical sporulating 

 ones, also were positive in five or -ix of 

 these tests. Two-thirds of the strains la- 

 beled Nocardia gave negative results in four 

 to six of the same tests. Of the remaining 

 third of the strain- received a.- Nocardia, 

 •J I had the same reactions as accepted 

 strains of Streptomyces and were assumed to 



