Multiple improvement of astaxanthin biosynthesis in Xanthophyllomyces dendrorhous by a combination of conventional mutagenesis and metabolic pathway engineering.

Xanthophyllomyces dendrorhous (Phaffia rhodozyma) is the only yeast or fungus that synthesizes the commercially attractive carotenoid astaxanthin. For a suitable bioprocess, the wild type has to be modified for increasing biomass content. To achieve this, a two step strategy has been followed. At first, random mutagenesis was applied leading to colonies with substantially higher astaxanthin content. Then, the resulting strain was genetically engineered by targeting limiting reactions for further enhancement of astaxanthin biosynthesis. This combinatorial approach together with selection of an appropriate growth medium resulted in highest astaxanthin biomass contents reported to date for X. dendrorhous. In a fermenter culture, its maximum content was 9.7 mg/g dry weight.