Research and Development of Cultivation Strategies for Biotechnological Mevalonic Acid Production by Saccharomycopsis fibuligera (poster)

C.F. GONZÁLEZ; L. RUBINSTEIN; LEDESMA P.; M.A. POLTI; J.I. FARIÑA; L.I.C. FIGUEROA

Los Angeles

Congreso; 100th GENERAL MEETING OF THE AMERICAN SOCIETY FOR MICROBIOLOGY; 2000

ASM

Mevalonic acid (MVA) is an important intermediate in the synthesis of various isoprenoids such as cholesterol. By virtue of its ability for promoting growth, MVA is frequently employed as a growth factor for microorganisms and plants. It is furthermore used as a precursor for fat soluble vitamins, pyrethroid pesticides, ubiquinone, dolichol and carotenoids production. The availability of natural MVA is scarce and therefore, synthetic racemates have been employed in conventional studies until present. On this context, we have focused our work on the microbiological MVA production for its posterior use as a promoter for astaxanthin biosynthesis in the hyperproducing mutant yeast Phaffia rhodozyma PAC-1D. Previous reports indicate that MVA production might be faced by the cultivation of the yeast Saccharomycopsis fibuligera, though depending on the selected strain, yields are not always high enough for its application at fermenter scale and a critical evaluation must be carried out. Among the different factors affecting MVA production, particular attention has been paid to the composition of culture medium and the fermentation technologies used. In this work the yeast Saccharomycopsis fibuligera DSM 70554 was selected for MVA production development studies. Initially three different basal media were used (g/l); Medium I: yeast extract, 5 + glucose, 20; Medium II: yeast extract, 1 + glucose, 20 and Medium III: YNB (Difco) 0.67 + peptone, 0.1 + glucose, 20 (buffer controlled pH at 5). The improvement on the MVA excretion was intended by means of the addition of Tween 20 (1 g/l), Tween 80 (1 g/l), Triton X-100 (1 g/l), p-aminobenzoic acic (PABA, 600 µg/l) and sodium acetate (1 g/l). Preliminary screening of culture media was carried out at shake flask scale with an endpoint process evaluation involving the determination of intra- and extracellular MVA by HPLC, biomass dry weight and residual glucose. After 48 h of cultivation MVA production was detected under all conditions tested. At this time, two main parameters were considered for medium selection: extracellular MVA concentration and extracellular : intracellular MVA ratio. On this basis Medium I supplemented with Triton X-100 led to the best yields, with 0.26 g/l extracellular MVA and 1.4 extracellular : intracellular MVA ratio. The selected medium was then used for experiments at fermenter scale and much higher yields were achieved, with high extracellular MVA concentration and extracellular : intracellular MVA ratio. In addition, residual glucose was almost negligible, which meant an optimum use of the carbon source as compared with previous reports (> 5% residual glucose). Other advantage considering the downstream processing design was the high extracellular : intracellular MVA ratio indicating no need of cells disruption which usually involves high costs and operation times.