Acknowledgements

First of all, I would like to express my deep sense of respect and sincere gratitude to Prof. Dr. Elmar Heinzle for providing me a Ph.D. position and for his valuable guidance, stimulating discussion, and constant supports throughout the course of this work. I especially would like to thank him for giving me brilliant directions and his continuous help in solving problems. I would like to express my appreciation to Prof. Dr. Dietrich Volmer for his kind review of this thesis. My great thanks go to Dr. Taehoon Yang for his fruitful discussion on metabolic flux analysis and his XFLUXGATE program which are extremely critical to my project. I especially want to express gratitude to my colleagues. Without the generous help of you all, this thesis would not have been possible. Many thanks to Michel Fritz and Dr. Klaus Hollemeyer for their most valuable assistance of GC-MS, HPLC and MALDI-TOF MS analysis, as well as very useful suggestions. Thank Dr. Susanne Kohring, Robert Schmidt and Veronika Witte for their valuable support. I would like to thank Dr. Fozia Noor for her English correction of my thesis and advices for my work. I thank Verena Schütz for her kind help on my living here in Saarbrücken and fruitful discussions on my project. Thank