Abstract:
Optimal conditions for growth and bioconversion of plant sterol into steroid intermediate by Mycobacterium fortuitum CBS 313.79 were investigated. The suitable medium compositions for inoculums were nutrient broth supplemented with 1.0 g/l yeast extract, 5.0 g/l glycerol and 1.0 g/l tween 80. The optimal medium compositions for bioconversion of plant sterol into steroid intermediate, 4-androstene-3, 17-dione (AD), consisted of termarmyl-hydrolyzed starch having 20.8% (w/w) of reducing sugar or 0.8% (w/w) of glucose with 5.0 g/l of total solid content as a carbon source, (NH₄)₂HPO₄ at a total nitrogen content of 0.50 g/l as a nitrogen source, 0.50 g/l of KH₂PO₄, 3.0 g/l of CaCo₃, 2.0 g/l of MgSO₄, 0.4 g/l of NaCl and plant sterol dissolved in chloroform at 0.84 mg/ml of the medium as a substrate. The medium was adjusted to pH 7.0-8.0. Under the suitable growth conditions which were at 30℃ with 200 rpm shaking for 5 days, 83.6% bioconversion of sterol to AD was obtained. Furthermore, conditions for extraction and purification of AD from the fermentation broth were also reported. The suitable solvent for extracting was ethylacetate. The ratio between culture broth and the solvent was 1:2 (v/v). Extractionwas carried out 2 times for 15 minutes each. Under these conditions, 97.99% of AD with respect to the amount present in the broth was recovered. It was purified by chromatography on silica gel column twice. The first silica gel column chromatography was eluted with a mixture of ethylacetate and chloroform at a ratio of 15:85 (v/v). The eluent was further chromatographed on a second silica gel column eluted with cyclohexane mixed with ethylacetate at a ratio of 4:1 (v/v). The eluent was evaporate. AD was crystallized by using the mixed solvent of ethylacetate and hexane. White crystal was obtained with 18.6% recovery and 97% purity. Chemical analyses of the crystal in comparison with standard AD which were melting point, mass spectroscopy, infrared spectroscopy and proton-nuclear magnetic resonance confirmed that the compound obtained was 4-androstene-3, 17-dione.