As carbon emissions reach record levels annually, the allure of cyanobacterial biotechnology becomes increasingly desirable. The technology to receive a variety of renewable chemicals in exchange for CO2 and light is available, but many advancements are required before it can be commercially applicable. The focus of this dissertation is to improve the potential of cyanobacterial co-culture systems for photosynthetic bioproduction. The co-culture approach offers a degree of flexibility in output products that is difficult to match using other metabolic engineering approaches, and the overall sucrose production from cyanobacteria is promising relative to other carbohydrate feedstocks. Nonetheless, at this time, any attempts to scale cyanobacterial co-culture to industrially relevant volumes are likely to encounter various challenges. My dissertation research focused on two potential weaknesses of cyanobacterial co-culture. In Chapter 2, I describe my research to maximize the output of sucrose by modulating the cultivation conditions for sucrose-secreting strains of Synechococcus elongatus PCC 7942. Maximization of heterotrophic yield in co-culture is directly linked to the amount of fixed carbon that can be supplied by the cyanobacterial partner, and I interrogated a number of different illumination conditions and methods for providing inorganic CO2 to cyanobacterial strains. In Chapter 3, I describe my efforts to rationally design co-cultures for higher resilience and productivity through engineering in a system for physical attachment between the heterotroph and cyanobacterial partner. Specifically, I expanded upon prior work on a cyanobacterial surface display system with the long-range goal of installing extracellular binding domains on the surface of S. elongatus that could be used to mediate direct physical attachments with other proteins displayed on the surface of an engineered heterotrophic partner. Finally, in Chapter 4, I review the outcomes and conclusions of my research program and reflect upon both my experience and future prospects for the topic areas central to my dissertation.
Read
