engleski

OTC-deleted mutants of Streptomyces rimosus synthesize oxytetracycline

S. rimosus R6, the oxytetracycline (OTC) producer, has been characterized genetically and physically. The OTC-cluster was cloned and a restriction map derived. A physical map of the 8 Mb linear chromosome shows that it lies in a 'genetically-silent' region, some 600 kb from one chromosome end, which accounts for its frequent spontaneous amplification and deletion. Class II mutants (e.g. MV9, MV11 and MV15) delete one chromosomal end including the whole cloned OTC-cluster. However, pseudo-revertants of the Class II mutants that had regained the antibiotic activity were isolated ('Class IIR'). Seven independent mutants in the Class IIR category were isolated, all of them appear spontaneously from the Class II strain MV9. By colony morphology and the antibiotic yield they can be grouped in two sub-classes. The strains MV9R-1, MV9R-4 and MV9R-5 sporulate abundantly, while the sporulation of strains MV9R-2, MV9R-3, MV9R-6 and MV9R-7 is like that of the wild type R6. The biological tests show that the second sub-class produces as much antibiotic as the strain R6, while the first sub-class produces 10 to 20 times less antibiotic. The compound made by these Class IIR isolates was identified as OTC in three different TLC systems. More detailed investigation of the progenitor Class II mutants has revealed that they also synthesize an extremely small amount of OTC (about 0.1  g/ml) as identified by both TLC and HPLC. Further analysis of parameters of OTC biosynthesis of these two sub-classes has confirmed the results of biological tests. These data suggest the existence of a second otc cluster on S. rimosus chromosome.

Streptomyces rimosus; oxytetracycline; deletion mutants

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