By Yarrowia Lipolytica
Total Page:16
File Type:pdf, Size:1020Kb
Enhancing CO2 fixation by synergistic substrate cofeeding by Nian Liu B.S. Chemical Engineering, University of California, Berkeley, 2014 SUBMITTED TO THE DEPARTMENT OF CHEMICAL ENGINEERING IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN CHEMICAL ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY September 2020 © 2020 Massachusetts Institute of Technology. All rights reserved. Signature of author ............................................................................................................................. Department of Chemical Engineering July 1, 2020 Certified by ........................................................................................................................................ Gregory Stephanopoulos William Henry Dow Professor of Chemical Engineering and Biotechnology Thesis Supervisor Accepted by ....................................................................................................................................... Patrick S. Doyle Robert T. Haslam (1911) Professor of Chemical Engineering Graduate Officer Enhancing CO2 fixation by synergistic substrate cofeeding by Nian Liu Submitted to the Department of Chemical Engineering On July 1, 2020, in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Chemical Engineering at the Massachusetts Institute of Technology ABSTRACT The irrevocable rise of atmospheric CO2 levels has prompted the development of scalable carbon fixation technologies in recent years. To this end, biological non-photosynthetic methods serve as promising leads since they not only sequester CO2, but also convert it into a variety of value-added fuels, chemicals, and pharmaceuticals with high specificity. Additionally, as the organisms responsible for fixing CO2 derive energy from free electrons or electron carriers such as H2, the process can interface with existing photovoltaics to achieve a high energy efficiency (~8%) that outcompetes photosynthetic systems (<1%). In this thesis, we describe a non-photosynthetic CO2- fixation approach that sequentially utilizes an acetogenic bacterium and an oleaginous yeast to accomplish the conversion of H2/CO2 into lipid-based biodiesel with acetate as the key intermediate. Despite its feasibility, this two-stage system suffers from slow metabolism of the two chosen microbes. To remedy the issue, we began by identifying the limiting factors, which was determined to be insufficient ATP availability for CO2 fixation in the first stage and inadequate NADPH levels for acetate-driven lipogenesis in the second stage. Correspondingly, a dual carbon source cofeeding scheme was developed to promote mixed substrate metabolism in the two organisms, synergistically stimulating CO2 reduction into products. We demonstrate that minor amounts of glucose addition to acetogen cultures saturated with H2 enhances net CO2 conversion into acetate by simultaneously satisfying ATP and e− demands at the appropriate ratio. Similarly, feeding the resulting acetate in conjunction with small quantities of gluconate balances the supply of carbon, ATP, and NADPH, which significantly accelerates lipid formation. The work advances our understanding of systems-level control of metabolism and can be applied to many other situations as an alternative tool for enhancing strain performance in metabolic engineering. Many products other than biofuels can also be synthesized from CO2 using the two-stage non- photosynthetic design as long as proper organisms are employed. As such, in order to expand the utility of the process, we also developed a data-driven host selection framework. By implementing a recommender system algorithm on strain-product-titer information collected from literature, we aimed to systematically summarize the criteria used for choosing an organism given a certain product of interest and vice versa. The results revealed an implicit principle that governs the selection of model versus non-model host organisms, which could benefit many industrial biotechnological applications. Thesis Supervisor: Gregory Stephanopoulos Title: Willard Henry Dow Professor of Chemical Engineering and Biotechnology 3 4 Acknowledgements To say that my six years of going through grad school was a ‘journey’ would be a massive understatement. It is by no means an exaggeration that the hardships I endured and the emotional swings I felt parallels that of Frodo as he crossed Middle Earth to reach Mount Doom (pardon my nerdy reference here). Although my PhD experience comes nowhere close to as exciting as his adventures (and it is probably best to leave it that way), I find peace in my mind knowing that we share something in common: Frodo always had his sidekick Sam close by his side to carry his footsteps onward when the need arose; I, too, had countless friends, families, and mentors who became the very giants that shouldered me throughout my research endeavor. Needless to say, I feel incredibly lucky and grateful to have everyone as part of my life here at MIT. First and foremost, I would like to express my sincerest gratitude towards my thesis advisor, Professor Gregory Stephanopoulos. Funnily enough, as part of a research group that specializes in metabolic engineering, I have rarely done much of the actual engineering, which at times brings me to question myself as to whether I am doing the right thing. Greg, on the other hand, never doubted my ideas and was patient enough to put up with a lot of the nonsense that I have thrown around throughout the years. I can confidently say that I would not have seen any of my projects through without his continued belief in my skills. His focus on impact and the utility of research have also been invaluable in pushing me to pay close attention to the big picture, in addition to laying a solid scientific foundation. All of his guidance and the resources he placed at my disposal, shaped me into the scientist I am today and for that, I am very thankful. Additionally, I would like to extend my acknowledgements to the rest of my thesis committee members, Professor Charles Cooney and Professor Richard Braatz, for their insightful comments and encouragements. The discussions we had during our meetings inspired me to look into areas beyond metabolic engineering and helped me build confidence in conducting scientific research. I am also indebted to Junyoung Park, whom I had the pleasure to collaborate with on the cofeeding project. In addition to the wealth of knowledge in cellular metabolism that he has imparted to me, what he has truly taught me is how to approach scientific research in general. Through our interactions, I have learned from him to design my experiments with a purpose in mind and to dig through my data extensively before rushing to the next experiment. Although he would always claim that these principles help him minimize manual labor and indulge on his ‘laziness’, I still hold him in the utmost respect as one of the best scientists I have had the honor to work with. Outside of lab and work, I regard Jun as a close friend and we had many interesting conversations and risky bets. Hopefully in the near future, I can finally cash in on some of the delicious Korean barbeque that he has promised me in LA. There are a number of other lab members and collaborators that I would like to thank as well. Yuting Zheng and Thomas Wasylenko were the first people who trained me when I joined the lab. With no prior experience in biology at all, it is a miracle I have made it this far and I owe it to both of them for helping me take the initial step. Kangjian Qiao was another postdoc in the lab I deeply respect. Much of his advice guided me through grad school, avoiding some of the common pitfalls, and I still discuss with him these days about planning my career. I interacted quite heavily with Zbigniew Lazar, who taught me a lot of neat tricks in molecular biology. Our interactions have really made the time I spend in lab much more enjoyable and I am honestly happy to have him as ‘my friend’. I have also had the pleasure to learn from Benjamin Woolston and his immeasurable 5 depth of knowledge in biotechnology and analytical chemistry. His actions have always inspired me to probe the fundamentals of every scientific aspect and not be content with superficial understandings. The time I spent with these mentors have really prepared me in becoming an independent researcher early on during grad school, which I leveraged to build many fruitful collaborations. In particular, I would like to acknowledge Junichi Mano for research on acid whey utilization, Suvi Santala and Ville Santala on wax ester production, David Emerson on acetogen metabolism, and Xiang Ji on microbial electrosynthesis. Of course, none of this would have been possible without the support from our lab’s administrative assistants, Rosangela dos Santos and Nicholas Pasinella, who worked tirelessly to take care of the mundane tasks and offered help whenever needed. Outside of research, I also have to thank a number of people in lab who I have had a lot of fun with. Jack Hammond was one of the few people I knew here that shared the same passion for gaming as I do. In many cases, I felt our personalities and general ‘chill’ attitudes were largely similar, which was refreshing in this hypercompetitive environment. I had many chats with Boonsum Uranukul and Alkiviadis Chatzivasileiou over coffee (despite me not drinking coffee), going over the small details of grad school life and the hardships associated