Cyanobacterial Biotransformations

Biotechnological processes offer clean and sustainable conditions for challenging chemical reactions. Many biocatalytic reactions, however, require the supply of chemical energy in form of donor substrates. These cosubstrates are usually sugars or petrochemicals. Microalgae have the unique ability to generate chemical energy by photosynthesis, which allows the substitution of organic cosubstrates by water, a clean and in large quantities available resource. The project investigates the effect of synthetically useful reactions on the energy metabolism in cyanobacteria. Focus lies on the understanding, how the cells adapt to stress caused by the reactions. This includes the formation of oxygen radicals by their own photosynthesis. A second risk is the depletion of the energy supply by the biotechnological process as additional consumer. The project studies the genetic adaptation of the cells to the conditions of the catalytic process. Then we will investigate strategies to achieve a balance between photosynthetic energy supply and consumption by catalytic reactions. A targeted reduction of non-essential protection mechanisms against fluctuating light is a promising approach to direct the energy metabolism towards the desired biotechnological reactions. Understanding the physiological effects of light-driven biotransformations and potential strategies for their improvement by cell engineering is an important basis to establish cyanobacteria as clean production organisms for the sustainable synthesis of chemical and pharmaceutical products. 1

Oxidative-reductive transformations belong to the most important reactions in organic synthesis. A large number of oxidoreductases catalyse the introduction and modification of functional groups under mild reaction conditions and with often outstanding selectivity. Microalgae have the unique ability to generate chemical energy by photosynthesis, which allows the substitution of organic cosubstrates by water, a clean and in large quantities available resource. The project CyanoBiotrans investigated the physiological effect of synthetically useful reactions on the energy metabolism in cyanobacteria. The supply of photosynthetic electrons was identified as limiting factor for the light-driven biotransformation reactions. Furthermore, the deletion of a competing electron-consuming process could be shown to increase the reaction rate. This result shows metabolic engineering as promising avenue for the further optimization of the productivity of photosynthetic bacteria as production organisms for environmentally-friendly biocatalytic processes.