XAKIATIONS. Ml 'I'AI'IOXS, AM) A I )AI' I A'lMO.XS 



111 



plasm. Tlu'sc lu'tcrokaiyons can ho pci'pclu- 

 atcd l)y traj^nuMits of \(\<i;('la(i\(' mycelium, 

 hut not by spores; the lat ler are uiiimicleate, 

 l)eiiis cicn\-e(l from a siii<>;le nucleus. .V 

 strain of N. coclicolnr forminj"; stahle hetero- 

 kaiyons and i)roilucinji; spores wiih at least 

 two sets of genes was studiecL Xutritionally 

 wild type, or prototrophic, colonies were 

 ohtained from growth-factor-dependent, or 

 auxotropliic, combinations hy two metiiods: 

 (a) strains W(M-e plated together on a minimal 

 nunlium; the prototrophs arose after S to Hi 

 days; (h) strains were grown together on 

 complete medium for '.] to (J days; the result- 

 ing spores were transferred to minimal me- 

 diimi to .select prototrophs, which were puri- 

 lied by several serial tran.sfers on complete 

 medium. 



Bradley (1958) exposed a population of a 

 single strain of S. griscus, for se\eral grcjwth 

 cycles, to a sterile culture filtrate of another 

 strain of 5. griscus. The first accjuired several 

 genetic characteristics of the .second strain, 

 namely, streptomycin sensitivity changed to 

 resistance, bacteriophage .sensitivity changed 

 to resistance, absence changed to presence 

 of soluble pigment, and presence changed 

 to absence of pigment in the vegetati\'e my- 

 celium. The filtrate contained a low con- 

 centration of streptomycin, which did not 

 inhibit the growth of the first strain, but 

 streptomj'cin-resistant mutants were se- 

 lected. The observed morphological changes 

 were coupled with bacteriophage and strep- 

 tomycin su.sceptil)ility. The hybridization 

 was .said to be the result of selection of nui- 

 tants rather than gene transfer. 



Alikhanian and Alindlin grew biochemical 

 mutants of ^S. rimosus on suitable agar media, 

 and observed that at the point of contact of 

 the mutant colonies more abundant growth 

 and more abundant sporulation occurred. 

 Nuclear fusion and reduction occur in *S'. 

 coelicolor somewhere l)etween hyphal fusion 

 in the substrate mycelium, allowing hetero- 



• • < » [ . ^ 



•y- «»• 



Figure 53. J'ormatioii of heterokaryotic col- 

 onics of S. fradiae on minimal agar. Plates 1 and 

 3 seeded with 10' spores of strain 6F4-1 (methio- 

 nine and isoleucine requiring, and streptomycin 

 sensitive) and 6FS-16 (histidine and argininc rc- 

 fiuiring, and streptomycin resistant), respectively. 

 Plate 2 received a mixture of parental spores and 

 sliows formation of prototrophic colonies (Re- 

 ])roduced from: Braendle, D. H. and Szyi)alski, W. 

 I'roc. Nat. Acad. Sci. V.\: 947 !)o,5, 1957). 



karyosis and spore production in the aei'ial 

 hyphae (llopwood). 



According to Braendle and Szyljalski, aW 

 of the wild-type strains of Streptomyces 

 studied wei'e prototrophic, i.e. they formed 



