PUB - Publikationen an der Universität Bielefeld

In the light of the depletion of fossil fuel reserves worldwide, the search for sustainable and more environmental friendly alternatives becomes decisive. The generation of liquid fuels as bioethanol or biodiesel from biomass are already considered as economically viable options. However, conflicts of interest arise when the generation of food or animal feedstock competes with biomass production for conversion to biofuels. The use of microalgae could offer a possible solution to several of these problems; however a more wide-spread use is hampered by the requirement of suitable strains for bulk chemical generation. Though a lot of effort has been spent in finding suitable strains in the past years, much of the potential that can be found in the biodiversity of algae remains untouched. In this work, microalgae that originated from established strain collections but have not been in the focus of biofuel-related research before were investigated on their potential for liquid biofuel production. This approach was complemented by the isolation of new strains from mainly local freshwater and marine water bodies, followed by a detailed characterization in terms of biomass and lipid productivity as well as of their fatty acid profiles. The genus Monoraphidium could be identified as highly interesting for these purposes, since many members show robust growth and considerably high lipid productivities. Two strains of interest, Monoraphidium contortum and Monoraphidium neglectum, were investigated in detail and compared to the model organism Chlamydomonas reinhardtii. Both Monoraphidium strains showed a pronounced increase of neutral lipids under nitrogen starvation which could be furthermore enhanced in lower culture densities, consequently resulting in better light availability for the cells. The accumulation of lipids was not only superior to that of C. reinhardtii but also resulted in a fatty acid profile with a dominance of C18:1 and C16:0 fatty acids, which is promising for liquid biofuel generation. In addition, cells of M. neglectum were found to increase their size at defined salt concentrations, thereby offering the possibility for facilitated down-stream processing. Key element for liquid biofuel production is the content of neutral lipids, namely triacylglycerol (TAG), in the biomass. The elucidation of pathways for TAG synthesis is currently subject to intense research efforts. Therefore the role of two distinct metabolic pathways was investigated in more detail in the model organism C. reinhardtii. To gain further insights into the lipid metabolism of Monoraphidium and to allow targeted improvement of these strains, the genome of M. neglectum was sequenced. The annotation of pathways of fatty acid synthesis as well as within the glycerolipid metabolism allowed not only detailed insights into the diversity of oleaginous organisms, but also leads to further promising targets to improve this strain. Within this work, the Selenastraceae could be identified as a highly interesting family with a number of interesting strains for biomass generation that also have a high potential for subsequent conversion to liquid biofuels. The sequencing of Monoraphidium neglectum was performed to establish this species as future model organism for the other members of this family and also opens the possibility for future targeted engineering approaches.