Date of Award
Doctor of Philosophy (PhD)
Microbial biosynthesis has produced a variety of complex compounds using processes that are more environmentally-friendly than many conventional methods. The most common hosts are heterotrophs, which require the addition of an organic carbon source; while cyanobacteria possess many traits that make them a more sustainable biotechnology platform. As phototrophs, cyanobacteria can employ sunlight and carbon dioxide to create many value-added compounds. A wealth of tools has been developed to engineer the commonly used heterotrophs for higher yields and titers; yet, few synthetic biology tools have been designed for cyanobacteria. Furthermore, many of the tools created for heterotrophs do not function as designed in the photosynthetic organisms. We developed a multi-input and several single-input transcriptional regulators for the model cyanobacterium Synechocystis sp. PCC 6803 to address this problem. These circuits were designed to respond to industrially-relevant signals, including oxygen, light and the cells' nitrogen status, in addition to an inexpensive sugar. The two-input AND logic gate we built adds more sophisticated heterologous gene expression to the cyanobacterium's synthetic biology toolbox. The addition of these regulators provides engineers more options when looking for a part that meets the needs of the situation. This was demonstrated by our use of the oxygen-responsive promoter to express, in a heterologous host, genes from a cluster that encodes nitrogenase. This new device can be used to probe the regulation of nitrogen fixation in a photosynthetic cell. Our development of genetic circuits for transcriptional regulation in Synechocystis sp. PCC 6803 improves the viability of this photosynthetic host in biotechnology.
Tae Seok Moon
Gautam Dantas, Marcus Foston, Elizabeth Haswell, Himadri Pakrasi