Abstract
The present study aimed to construct superior Streptomyces bacteria for improvement antibiotic production with mutagenic agents treatments and protoplast fusion techniques. Two Streptomyces sp. were applied in this study i.e. S. fradiae KCC-5-0133 and S. endus KCC-5-0213. The obtained interspecific fusants were used as biological control agents against Fusarium oxysporum, Alternaria solani and Streptomyces scabies. Treatment of wild type strains with different concentrations of MNNG for one hour showed that, out of 79 isolates obtained from S. fradiae, 17 isolates excelled the wild type in antibiotic production. When MNNG was applied with S. endus at different concentrations and the same exposure time, 21 isolates out of 83 ones exceeded its parental strain. Wild type strains treated with EMS showed that out of 100 isolates from S. fradiae, 21 isolates proved to be higher than the parental strain in antibiotic production. Eighteen isolates, out of 100 were selected randomly from S. endus, for their highest in antibiotic production. Protoplast fusion technique was applied between the selected survivors following the application of MNNG and EMS treatments. The highest and the lowest efficient antibiotic producer isolates, as well as, the parental strains were used. Nine crosses were carried out; the first cross involved the two parents (S. fradiae KCC-5-0133 and S. endus KCC-5-0213). The second to the fifth crosses involved four isolates selected from the survivors resulted from treatment both S. fradiae and S. endus with MNNG mutagen. Meanwhile the sixth to ninth crosses were performed between four isolates selected from the survived isolates following treatment of S. fradiae and S. endus with EMS mutagen. In general, interspecific protoplast fusion in the present study produced some new constructed isolates; Twenty out of 26 fusants lost their ability of inhibition zone formation with the tester strains. All of the six effective fusants were similar to the parental strains since they were effective with M. luteus tester strain. Moreover, three out of six interspecific protoplast fusants proved to be promising ones in biological control of plant pathogens. Two different pathogenic fungi (A. solani and F. oxysporium) and Streptomyces scabies which cause common scab in potato were used to determine the biological control efficiency of Streptomyces strains as well as their fusants. The obtained results clearly exhibited that only three out of the obtained 26 interspecific fusants proved to be highest effective ones for inhibition the growth of both A. solani and F. oxysporium fungi. The three effective isolates have the same or exceeded the effect of the parental strain S. endus KCC-5-0213. On the other hand, these effective interspecific fusants proved to be highly effective for Streptomyces scabies control as the other parental strain (S. fradiae KCC-5-0133) do.