Optimization of 1,18-octadecenedioic acid synthesis via biotransformation by the use of Candida tropicalis

For the production of polyesters diols and dicarboxylic acids are used. These raw materials usually are made from crude oil. Long-chain dicarboxylic acids (DCA) are promising compounds for the synthesis of polymers with new characteristics, but long-chain DCA are difficult to produce and expensive. Especially unsaturated DCA with more than twelve carbon atoms are currently not available from petrochemical raw materials. For the production of biobased polymers long-chain DCA can be produced via biotransformation for instance with yeast of the genus Candida. For this conversion a metabolic pathway called ω-oxidation is required. Alkanes and fatty acids are oxidized at their terminal methyl group in three enzymatic steps. By blocking degradation of DCA via deletion in the -oxidation pathway an enrichment of dicarboxylic acids in the supernatant of the culture is possible.
Candida tropicalis is a known DCA producing strain of long-chain dicarboxylic acids. In our experiments we first screened different substrates like oleic acid methylester derived from rapeseed oil and olein and determined their conversion rates. Candida tropicalis was not able to convert crude rapeseed oil into DCA itself, but only when lipase was added into the bioreactor.
Within this work we established the biotransformation of oleic acid into the corresponding 1,18-octadecenedioic acid and the bioprocess in a 30 L fermenter. The process is divided into two main phases: an optimized cell growth phase with different fed batch strategies to avoid crabtree effect as well as production phase which require change of the pH and limiting amounts of C- and N-sources. We achieved biomass concentrations up to 40 g/L and DCA conversion rates of 0,44 g/(L h) and a maximum concentration of 100 g/L. Additionally we observed that the conversion is influenced by the concentration of ammonium in the medium.
In our future work we will focus on the establishment of new strains with even higher productivity.