Date of Award

Winter 12-15-2022

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Plant & Microbial Biosciences)

Degree Name

Doctor of Philosophy (PhD)

Degree Type



Through oxygenic photosynthesis, cyanobacteria, algae, and plants convert light into chemical energy. However, highly energetic light often damages the photosynthetic apparatus, which can lead to the decline of photosynthetic activity (photoinhibition), and prolonged photoinhibition can lead to cell death. Cyanobacteria enact various protective mechanisms to mitigate photodamage, many of which have been conserved in plants. Repair of PSII reaction centers, decreased light absorption, quenching of excess absorbed energy, and biosynthesis of antioxidants all work to mitigate damage during high light. Due to the adjustments to photosynthesis, acclimation to high light requires remodeling of cellular metabolism and physiology. Therefore, phototrophs have evolved a diverse set of regulatory systems that efficiently detect increased light and enact cellular responses. During this study, I have endeavored to understand the unique features of the fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 (Synechococcus 2973) that allow it to grow under extreme high light conditions.In Chapter 1, I have reviewed the current understanding of regulatory mechanisms that control gene expression and physiology for high light response. The interconnectedness of light response with nutrient metabolism demand is discussed and placed in the context of Synechococcus 2973. Chapter 2 takes a global look at the transcriptional changes that occur in two highly homologous Synechococcus strains during high light response and acclimation. Using this two-strain method, changes that are specific to Synechococcus 2973 were identified and discussed. Chapter 3 investigates a novel gene found to be involved in the high light tolerance of Synechococcus 2973. In Chapter 4, conclusions, future directions, and additional data are discussed. In the Appendices, specific polymorphic loci that allow for natural competence in Synechococcus 7942 were identified and a naturally competent Synechococcus 2973 strain was generated. In summary, this dissertation describes the unique ways in which a fast-growing cyanobacteria acclimates to high light, reports the importance of several genes in high light tolerance, and characterizes a conserved phosphatase required for light response in cyanobacteria.


English (en)

Chair and Committee

Himadri B. Pakrasi

Committee Members

Arpita Bose, Hani Zaher, Ram Dixit, Michael Caparon,