High production of D-β-hydroxyisobutyric acid from methacrylic acid by Candida rugosa and its mutant

Production of D-β-hydroxyisobutyric acid (D-HIBA) from methacrylic acid (MA) was investigated using Candida rugosa IFO 0750 and its mutant. Cell growth decreased as the MA concentration increased and was inhibited at D-HIBA concentrations higher than 30 g/l. Optimal MA concentration for D-HIBA production was in the range of 10-20 g/l. It was also noted that cell growth and D-HIBA production were inhibited by higher concentrations of Na⁺, K⁺, and NH₄⁺, which were required for pH control during cultivation. With a suitably designed feeding mode of MA, the parent strain produced 65 g/l of D-HIBA after 120 h of fed-batch cultivation, but molar conversion yield of D-HIBA was less than 40%. The mutant, unable to assimilate propionic acid, produced as high as 70 g/l of D-HIBA in the same culture period with a molar conversion yield of more than 70%.