Development of a Bioprocess for Squalene Production in Thraustochytrids

Squalene is a natural triterpene that has many applications in the pharmaceutical, cosmetic and food industry. The current production of this natural substance is problematic, as deep sea sharks are hunted for its extraction from shark liver oil. Extraction from certain lipid-rich plants is possible, but requires large amounts of land, is seasonal and runs the risk of competing with food production. Therefore, this work deals with an alternative approach: The biotechnological squalene production by marine eukaryotes belonging to the thraustochytrid family.

Thraustochytrids are unicellular eukaryotes that occur in marine habitats and are able to produce large amounts of lipids and store them in their cells. The proportion of squalene in the total lipid depends heavily on the chosen cultivation conditions.

In this work, the influence of oxygen-limiting conditions on the growth and squalene productivity of the wild-type Schizochytrium sp. S31 was investigated. For this purpose, the organism was cultivated in shake flasks and in a bioreactor using different cultivation strategies. Respiratory activity was monitored in both cultivation systems by analysing the gas composition of the exhaust gas or the headspace in real time. During fed-batch cultivation under oxygen-limiting conditions, a squalene yield of 1.1 g/L was achieved.

With the aim of a more cost-effective biotechnological production of squalene and the development of a circular process, the second part of this work dealt with the use of potential side streams as medium substitutes. The complex nitrogen source of the cultivation medium used for thraustochytrids was successfully replaced by biomass from the cultivation of the basidiomycete Pleurotus ostreatus. An extract rich in nitrogen sources was produced from the fungal components, especially the fungal mycelium, by enzymatic hydrolysis. The clarified extract was then used to cultivate the thraustochytrid Schizochytrium sp. S31 and its influence on growth and squalene productivity was determined.

Overall, this work demonstrated the positive influence of oxygen-limiting conditions on the squalene productivity of a thraustochytrid in different cultivation systems. In addition, it was shown for the first time that residual biomass from the submerged cultivation of the basidiomycete P. ostreatus can replace media components in biotechnological squalene production.