MIKROBIOLOGIESE PRODUKSIE VAN L-MALAAT

Abstract

L-Malic acid is of great importance in the food and beverage industries where it is being used as an acidulant, preservative and flavour fixative. A unique application of L-malic acid is the treatment of patients with inherited metabolic defects such as hyperammonemia. The D-isomer of malic acid does not occur in nature; for this reason, chemically synthesized DL-malic acid is not always acceptable for food and pharmaceutical use. Since L-malic acid is not produced commercially in South-Africa we investigated the possibility of producing it rnicrobiologically with the yeast Saccharomyces cerevisiae amplified for fumarase. We designed primers for PCR of the yeast fumarase gene (FUM 1 ). The PCR-products were cloned in an yeast expression vector. Functional PCR-clones were selected by complementation in a Saccharomyces cerevisiae respiratory defective strain, created by homologous recombination of a HIS3 deleted FUMl-sequence. Functional PCR-clones were used for overexpression of the fumarase protein in two different yeast strains. One of the strains showed 31-fold overexpression of the fumarase enzyme and was used for bioconversion of fumaric acid to L-malic acid. The productivity of the strain was higher than that of immobilized Brevibacterium strains previously used in the bioconversion of fumaric acid to L-malic acid.