66 



NATURE, FORMATION, AND ACTIVITIES 



cursors (like the acetate or propionate types) 

 of man}' well known secondary metabolites 

 are also intermediates of primary metabo- 

 lism. According to this concept, antibiotics 

 are to be looked upon as "waste" products 

 of the general metabolic reactions of the 

 organisms. 



Location of Antibiotics in the Producing 

 Organism 



The cells of bacteria and actinomycetes 

 may be considered as being made up of three 

 groups of constituents: cell walls, cell proto- 

 plasm, and slimy excretion products adher- 

 ing to the cells, such as capsules. The proto- 

 plasm comprises: (1) functioning elements, 

 notably nuclear material, enzymes and co- 

 enzymes, and other constituents that take 

 part in the growth and multiplication of the 

 cell; (2) metabolic constituents, including 

 sugars, amino acids, fatty acids, vitamins, 

 which are required for cell synthesis; (3) 

 waste products of metabolism; and (4) 

 storage or reserve materials (Holdsworth, 

 1952; Cummins, 1956; Cummins and Harris, 

 1956; Ikawa and Snell, 1956; Salton, 1956). 



The cjuestion under consideration is: 

 where do the antibiotics accumulate? The 

 cell wall is certainly a logical place for them. 

 Still, they may be considered as storage 

 materials and even as metabolites. It is true 

 that the organisms producing actinomycin 

 or streptomycin are no longer able to utilize 

 these antibiotics as nutrients. This may be 

 due, however, to a change in the chemical 

 structure of the compound after it has been 

 isolated from the medium, since in the cul- 

 ture itself the substances tend to l)e de- 

 stroyed after they have accumulated (see 

 also Wiebull, 1956; Work, 1957). 



As already mentioned, some antibiotics 

 such as streptomycin are mainly found extra- 

 cellularly in the culture medium. Others such 

 as perimycin are found only in the myceliimi 

 of the producing organism. Still others such 

 as candicidin are found in lioth locations. 



These facts raise a number of questions 

 which have not yet been successfully an- 

 swered . 



In our early studies on the formation of 

 streptothricin, it was observed that when a 

 culture broth was allowed to stand for 

 several days at the end of the fermentation 

 period, it tended to increase gradually in 

 antibiotic potency. This suggested that 

 streptothricin may have been originally 

 bound to some chemical constituent in the 

 cells of the organism; gradually this union 

 was freed from its association with another 

 compound by some enzyme system in the 

 culture. 



Eiser and AIcFarlane (1948) found that 

 the presence of NaCl increased the permea- 

 bility of the hyphae of Strepfomyces griseus 

 and allowed the liberation of streptomycin 

 at a greater rate than in the absence of the 

 salt. Only lysis of the mycelium served a 

 similar purpose, since after prolonged incu- 

 bation (6 days), the streptomycin in the 

 medium without the salt had risen to the 

 level of the medium with the salt. 



Perlman and Langlykke (1950) found that 

 large amounts of streptomycin occur bound 

 in the mycelium of the organism producing 

 the antibiotic. They suggested that the anti- 

 biotic may be a part of the cell wall of the 

 actinomycete. The bound streptomycin 

 could be released by treatment of the cells 

 with acid, alkali, or ionizable salts, as well as 

 by sonic vibrations. Perlman (1953) reported 

 that various other antibiotics, notably neo- 

 mycin and chloramphenicol, were also bound 

 to the mycelium of the organisms producing 

 them and could be released by various treat- 

 ments. The binding of the antibiotic was not 

 a simple ion exchange phenomenon, since 

 addition of streptomycin to the mycelium 

 did not result in adsorption of the antibiotic. 

 Although in our early studies NaCl was ob- 

 served to have a fa^'orable effect upon the 

 "production" of streptomycin, this effect was 

 explained as the result of the freeing of the 



