Abstract: Streptomyces roseoflavus NKZ-259 is a biocontrol strain and plant growth regulator indole-3-acetic acid（IAA）is produced in the process of secondary metabolism. The fermentation medium was optimized in this study in order to increase the content of IAA produced by a strain. The 6 optimal nutrients of fermentation medium were determined by single factor experiment,and they were glucose,soluble starch,peptone,potassium nitrate,dipotassium hydrogen phosphate,and L-tryptophan,respectively. Plackett-Burman design method was applied to screen major factors affecting the fermentation production of IAA,which was L-tryptophan,glucose,and dipotassium hydrogen phosphate. Central combination design（CCD）and response surface methodology were used to analyze the interactions of all factors. Finally,the optimized fermentation medium was composed as follow：L-tryptophan 2.24 g/L,glucose 20.7 g/L,dipotassium hydrogen phosphate 0.5 g/L,soluble starch 10 g/L,peptone 3 g/L,potassium nitrate 4.5 g/L. The concentration of IAA reached 45.377 4 μg/mL after the medium optimized,which was increased 3 times compared to the original fermentation medium.

Key words: indole-3-acetic acid（IAA）, fermentation medium, response surface methodology