62 



THE ACTINOMYCETES, Vol. II 



defined conditions of growth recognized. Un- 

 necessary media and nonessential details had 

 better be left out to avoid cumbersome de- 

 scriptions and nonduplicable characteris- 

 tics that may apply to varieties or strains 

 rather than to species. A larger number of 

 media and more detailed descriptions may 

 not only fail to give additional information 

 but may complicate the description of the 

 species to such an extent as to render the 

 identification of freshly isolated cultures 

 difficult. 



The composition of the media is usually 

 given first consideration for descriptive pur- 

 poses. According to Waksman (1958), Shi- 

 nobu (1958), and others, these media should 

 include: (a) at least three synthetic media, 

 preferably sucrose-sodium-nitrate-salt or su- 

 crose-ammonium-salt agar, glucose- or glyc- 

 erol-asparagine agar, and calcium malate or 

 calcium citrate agar; (b) two or possibly 

 three organic media, such as nutrient (pep- 

 tone-beef extract) agar, yeast extract-glucose 

 agar, potato-glycerol-glutamate agar, or oat- 

 meal agar; (c) three or four complex natural 

 media, notably potato plugs, gelatin, and 

 milk; (d) peptone-iron-yeast extract agar for 

 H2S production; (e) tyrosine medium for the 

 tyrosinase read ion; and (f) a synthetic me- 

 dium for carbohydrate utilization. 



Very few, if any, other media are required. 

 Liquid media, with the exception of those 

 previously listed, are better left out. 



Morphological Properties 



The method of study of the morphological 

 properties of the streptomycetes would in- 

 clude visual microscopic examination versus 

 electron microscopic studies; direct exami- 

 nation versus study of stained preparations; 

 and hanging drop versus agar surface cul- 

 tures. 



STRUCTURE OF SUBSTRATE MYCELIUM 



The substrate mycelium of a Streptomyces 

 does not, as a rule, segment spontaneously 



into bacillary or coccoid forms. It produces 

 leathery or tough-textured growth, remain- 

 ing nonseptate and coherent even in old 

 cultures. Although no true septa are ob- 

 served in young cultures, it has recently been 

 reported that older cultures show at least 

 occasional septal ion. The compactness of 

 this substrate growth is responsible for the 

 fact that liquid media are always clear, un- 

 less the culture has been subject to phage 

 or lytic action. 



NATURE AXD PROPERTIES OF AERIAL MYCE- 

 LIUM 



The aerial mycelium is usually thicker 

 than the substrate mycelium. While the 

 morphology of the substrate mycelium is 

 usually undifferentiated, the aerial mycelium 

 of streptomycetes, under fixed conditions of 

 culture, shows sufficient differentiation that 

 a miscellaneous assortment of isolates can 

 be segregated into a number of groups hav- 

 ing like morphological characteristics. This 

 is one of the most important criteria for 

 classification in the genus Streptomyces. Sev- 

 eral aspects relating to the aerial mycelium 

 may be considered: 



a. Gross macroscopic appearance. The rela- 

 tive abundance, structure (cottony, velvety, 

 powdery), formation of rings or concentric 

 zones, and pigmentation of the aerial my- 

 celium are important diagnostic criteria. 



h. Microscopic properties. The microscopic 

 structure of the aerial mycelium gives a clear 

 picture of the morphology and reproductive 

 structures of the organism. The hyphae may 

 be long or short, with extensive or little 

 branching. The branching may be simple or 

 complex, monopodial or sympodial, broom- 

 shaped or verticillate. The fruiting bodies or 

 sporophores are short or long, occurring sin- 

 gly, in clusters, or as verticils; they are 

 straight , wavy, or spiral-forming. The spirals 

 or coils are either long and open or short 

 and compact. Spiral formation may take 

 place on one medium and not on others. 



