ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: Biology
- All Subjects: Biofuel
- Creators: Krajmalnik-Brown, Rosa
This work begins by defining a working window of light intensity (LI). Wild-type and laurate-excreting Synechocystis required an LI of at least 5 µE/m2-s to sustain themselves, but are photo-inhibited by LI of 346 to 598 µE/m2-s.
Fixing electrons into valuable organic products, e.g., biomass and excreted laurate, is critical to success. Wild-type Synechocystis channeled 75% to 84% of its fixed electrons to biomass; laurate-excreting Synechocystis fixed 64 to 69% as biomass and 6.6% to 10% as laurate. This means that 16 to 30% of the electrons were diverted to non-valuable soluble products, and the trend was accentuated with higher LI.
How the Ci concentration depended on the pH and the nitrogen source was quantified by the proton condition and experimentally validated. Nitrate increased, ammonium decreased, but ammonium nitrate stabilized alkalinity and Ci. This finding provides a mechanistically sound tool to manage Ci and pH independently.
Independent evaluation pH and Ci on the growth kinetics of Synechocystis showed that pH 8.5 supported the fastest maximum specific growth rate (µmax): 2.4/day and 1.7/day, respectively, for the wild type and modified strains with LI of 202 µE/m2-s. Half-maximum-rate concentrations (KCi) were less than 0.1 mM, meaning that Synechocystis should attain its µmax with a modest Ci concentration (≥1.0 mM).
Biomass grown with day-night cycles had a night endogenous decay rate of 0.05-1.0/day, with decay being faster with higher LI and the beginning of dark periods. Supplying light at a fraction of daylight reduced dark decay rate and improved overall biomass productivity.
This dissertation systematically evaluates and synthesizes fundamental growth factors of cyanobacteria: light, inorganic carbon (Ci), and pH. LI remains the most critical growth condition to promote biomass productivity and desired forms of biomass, while Ci and pH now can be managed to support optimal productivity.
Sustainable global energy production is one of the grand challenges of the 21st century. Next-generation renewable energy sources include using photosynthetic microbes such as cyanobacteria for efficient production of sustainable fuels from sunlight. The cyanobacterium Synechocystis PCC 6803 (Synechocystis) is a genetically tractable model organism for plant-like photosynthesis that is used to develop microbial biofuel technologies. However, outside of photosynthetic processes, relatively little is known about the biology of microbial phototrophs such as Synechocystis, which impairs their development into market-ready technologies. My research objective was to characterize strategic aspects of Synechocystis biology related to its use in biofuel production; specifically, how the cell surface modulates the interactions between Synechocystis cells and the environment. First, I documented extensive biofouling, or unwanted biofilm formation, in a 4,000-liter roof-top photobioreactor (PBR) used to cultivate Synechocystis, and correlated this cell-binding phenotype with changes in nutrient status by developing a bench-scale assay for axenic phototrophic biofilm formation. Second, I created a library of mutants that lack cell surface structures, and used this biofilm assay to show that mutants lacking the structures pili or S-layer have a non-biofouling phenotype. Third, I analyzed the transcriptomes of cultures showing aggregation, another cell-binding phenotype, and demonstrated that the cells were undergoing stringent response, a type of conserved stress response. Finally, I used contaminant Consortia and statistical modeling to test whether Synechocystis mutants lacking cell surface structures could reduce contaminant growth in mixed cultures. In summary, I have identified genetic and environmental means of manipulating Synechocystis strains for customized adhesion phenotypes, for more economical biomass harvesting and non-biofouling methods. Additionally, I developed a modified biofilm assay and demonstrated its utility in closing a key gap in the field of microbiology related to axenic phototrophic biofilm formation assays. Also, I demonstrated that statistical modeling of contaminant Consortia predicts contaminant growth across diverse species. Collectively, these findings serve as the basis for immediately lowering the cost barrier of Synechocystis biofuels via a more economical biomass-dewatering step, and provide new research tools for improving Synechocystis strains and culture ecology management for improved biofuel production.