Summary

In the LEDCyans project, phototrophic cultivations of cyanobacterium Synechocystis sp. PCC 6803 will be performed and monitored in a photocultivation system comprising two innovative shake flasks technologies. These technologies are a novel LED illumination module (LEDitSHAKE, Fraunhofer IME), which allows the irradiation of shake flask cultures with light of different wavelength and intensity, and the Respiration Activity MOnitoring System RAMOS. The cultivation system will be used to optimize the cultivation conditions of Synechocystis sp. PCC 6803. Thereby, product yields for two distinct processes will be maxmized. The two model products are squalene and sucrose. Squalene is a high-value product with applications in the pharmaceutical and cosmetic industries. Therefore, the carbon flux in Synechocystis sp. PCC 6803 will be directed towards squalene production by integrating an inducible overexpression of squalene synthase. For the second process, Synechocystis sp. PCC 6803 will be genetically equipped with the sucrose transporter CscB, to convert light energy and CO₂ to the fermentable sugar sucrose that is secreted. By fixing CO₂ as a carbon source for heterotrophic organisms, the strains engineered in this project will be the basis for future co-cultivations with yeasts (e.g. Pichia pastoris) or fungi (e.g. Ustilago maydis) in sustainable bioprocesses. By monitoring the photosynthesis and respiration activity of the phototrophic cultivations, the direct influence of light color, light intensity and CO₂ partial pressure on the growth of Synechocystis sp. PCC 6803 and the final product yield will be investigated. Both targeted model processes will be scaled up into a 1 L stirred tank fermenter (Lambda laboratory instruments). As a quality criterion, the course of the oxygen and carbon dioxide transfer rates and the final product yields will be compared to the results from the shake flask experiments. The results from the fermenter cultivations will be used to generate a mathematical process model to perform an economic evaluation of the squalene and sucrose production and to assess the total carbon balance. The LEDCyans team consists of experts in cyanobacteria and process engineering. Furthermore, the application potential of an innovative photocultivation system as a platform technology for fast bioprocess development with phototropic microorganisms will be demonstrated.