Production of D S-threo-isocitric acid (ICA) by yeast meets serious difficulties since it is accompanied by a simultaneous production of citric acid (CA) in significant amounts that reduces the yield of desired product. In order to develop an effective process of ICA production, 60 yeast strains of different genera (Candida, Pichia, Saccharomyces, Torulopsis, and Yarrowia) were tested for their ability to produce ICA from rapeseed oil; as a result, wild-type strain Yarrowia lipolytica VKM Y-2373 and its mutant Y. lipolytica 704-UV4-A/NG50 were selected as promising ICA producers. The effects of temperature, pH, aeration, and concentrations of rapeseed oil, iron, and itaconic acid on ICA production by selected strains were studied. Under optimal conditions (pH 6.0; aeration 50-55 %; rapeseed oil concentration of 20-60 gl(-1), iron ion concentration of 1.2 mg l(-1), and itaconic acid amount of 30 mM), selected strains of Y. lipolytica produced predominantly ICA with a low amount of a by-product, CA.

Mycobacterium sp. VKM Ac-1815D and its derivatives with altered resistance to antibacterial agents were able to produce androst-4-ene-3,17-dione (AD) as a major product from sitosterol. In this study, those strains were subjected to subsequent mutagenization by chemical agents and UV irradiation in combination with sitosterol selection pressure. The mutant Mycobacterium sp. 2-4 M was selected, being capable of producing 9alpha-hydroxyandrost-4-ene-3,17-dione (9-OH-AD) as a major product from sitosterol, with a 50% molar yield. Along with 9-OH-AD, both AD and 9alpha-hydroxylated metabolites with a partially degraded side-chain were formed from sitosterol by the mutant strain. The strain was unable to degrade 9-OH-AD, but degraded androsta-1,4-diene-3,17-dione (ADD), thus indicating a deficiency in steroid 1(2)-dehydrogenase and the presence of 9alpha-hydroxylase activity.

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