Abstract: To determine the effect of constitutively overexpressed isoleucine dioxygenase gene (ido) on 4-hydroxyisoleucine production, an ido constitutively expressing plasmid pXM01-ido and a strain HIL017 harbouring the plasmid were constructed. The transcription level of ido and the activity of IDO in HIL017 were significantly increased as compared with those in HIL016, inductively expressing the gene. Moreover, 4-hydroxyisoleucine production by HIL017 was increased by 19.4%. To further improve 4-hydroxyisoleucine production, corn steep liquor, glutamic acid and FeSO4·7H2O were recognized as main medium components using the Plackett-Burman design. By using he steepest ascent method and response surface methodology the optimal values of these factors were determined as follows: corn steep liquor 34.1 mL/L, glutamic acid 2.98 g/L, and FeSO4·7H2O 0.016 7 g/L, giving a predicted yield of 5.57 g/L. Validation experiments showed that 4-hydroxyisoleucine production was 5.53 g/L, increasing by 19.7% compared with that before optimization.

Key words: 4-hydroxyisoleucine, isoleucine dioxygenase, Corynebacterium glutamicum, constitutive overexpression, response surface methodology