Heterotrophe und mixotrophe Kultivierung terrestrischer Cyanobakterien

Terrestrial cyanobacteria live in form of biofilms that adhere to surfaces and in which the cells are embedded in a matrix of extracellular polymeric substances (EPS). The EPS consists of various substances e.g fatty acids, polysaccharides and proteins and protects the organisms from dehydration. It has already been shown that EPS extracts of various cyanobacteria strains have an antimicrobial action against gram-positive, gram-negative bacteria, and yeasts. Although terrestrial cyanobacteria are phototrophic organisms, there are some species that are able to grow heterotrophically. The problem here is that most cyanobacteria are non-axenic cultures. However, this is essential for heterotrophic cultivation. In this work different methods to obtain axenic cultures have been developed and their applicability to several cyanobacteria strains has been investigated. Using two strains, the effect of a heterotrophic or mixotrophic process on growth behavior, the production of EPS and the antimicrobial activity as well as the composition of pigments was considered and compared with the results of phototrophic cultivation. In addition to the nutrition and use of different carbon sources, the influences of light intensity, cultivation time and system were investigated. The results suggest that the cyanobacteria strains used in this study have transport systems to take up certain mono- or oligosaccharides and use them to generate energy. With the help of qPCR it could be shown that the investigated cyanobacteria are able to grow heterotophically or mixotrophically and that the mixed cultures existed on average of 60 % to 100 % of cyanobacterial biomass with all carbon sources used and over the entire cultivation period. Experiments on the influence of the light intensity and carbon source concentration could mathematically model the heterotrophic and mixotrophic growth.