UC San Diego

Phytoplankton are central to biogeochemical cycling and climate regulation on Earth and have been utilized for various biotechnological applications, such as the production of high value nutraceuticals, chemicals and therapeutics. While phytoplankton depend on light for photosynthesis, they are not immune to the deleterious effects of ultraviolet radiation (UVR) that can be present in the water column to depths of up to 20 m. This dissertation investigates the genetic basis of UVR tolerance in a model cyanobacterium using the high-throughput genomic screening technique RB-TnSeq and identifies an important and previously overlooked leucyl aminopeptidase (LAP) with cysteinyl-glycinase properties. The LAP is conserved across many ecologically relevant species and may be a key component of the glutathione catabolism pathway, with a pH-dependence that modulates activity of the enzyme based on the photosynthetic activity of the cell. This dissertation also presents the first report of the distribution of mycosporine-like amino acids (MAAs) across the surface of the Southern Ocean on a transect from Eastern New Zealand to the Western Antarctic Peninsula. MAAs, small strongly UVR-absorbing synthesized by phytoplankton and many other organisms, are an effective sunscreen against photo-inhibition and provide a defense against the photooxidative stress of UVR. Correlations were found between MAA composition and phytoplankton taxa, as well as between the ratio of MAAs to chlorophyll-a and the mean UVR dosage experienced the month prior, establishing a baseline for the quantity and quality of this ecologically important bioindicator of UVR-stress. Additionally, a novel biotechnological application of phytoplankton is presented in which genetically engineered cyanobacteria are 3D printed into an alginate hydrogel, producing a stimuli-responsive photosynthetic living material with functional outputs useful for bioremediation and the capacity for inducible cell death to prevent biofouling of the environment. A final data chapter includes projects extending beyond studies of the ultraviolet to the genetic basis of tolerance of unique spectral qualities of light in a model cyanobacterium. Together, this dissertation integrates the interactions between phytoplankton and light, from environmental to genomic levels, and presents a novel biotechnological application of cyanobacterial strains as bioengineered components of a living material.