Bioreduction of phenylglyoxylic acid to R-(−)-mandelic acid by Saccharomyces cerevisiae FD11b

Abstract

Screening from 40 microorganisms belonging to different taxonomical groups ( Saccharomyces cerevisiae, Lactoballius, Streptococcus faecalis and Candida albicans) was performed to select the strain with high production rate of R-(−)-mandelic acid (R-MA). A sp. strain S. cerevisiae FD11b with high yield and enantiomeric excess (e.e.) and little byproducts was obtained by means of UV-mutation breeding. In the optimal conditions of pH 6.5, 32 °C, anaerobic and glucose supply rate ( F glu) 0.0833 mmol gdw −1 h −1, the strain FD11b showed a high specific MA production rate ( q p = 0.35 mmol gdw −1 h −1) and enantioselectivity (e.e. = 97.1%). The phenylglyoxylic acid (PGA) concentration showed a remarkable effect on the apparent activity of MA dehydrogenase. The specific production rate ( q p) reached the maximum at 30–40 mM of PGA concentrations. At higher concentrations of PGA more than 40 mM, the q p decreased obviously in a linear way. However, the e.e. of R-MA kept about 95–96.5%, when the PGA concentration was below 60 mM, even at the concentration of PGA 80 mM, the e.e. was still higher than 90%. A modified Monod type equation based on a hypothesis of substrate inhibition could fit the experimental data well. The estimated maximum specific production rate ( q pm) and saturation constant ( K s) were 0.431 mmol gdw −1 h −1 and 5.88 mM, respectively.