@phdthesis{oai:oist.repo.nii.ac.jp:00001534,
 author = {Mars Brisbin, Margaret},
 month = {2020-06-01, 2020-06-01},
 note = {Microbial eukaryotes (protists) are important contributors to marine biogeochemistry and play essential roles as both producers and consumers in marine ecosystems. Among protists, mixotrophs—those that use both heterotrophy and autotrophy to meet their energy requirements—are especially important to primary production in low-nutrient regions. Acantharian protists (clades E & F) accomplish mixotrophy by hosting ​Phaeocystis spp.​ as algal endosymbionts and are extremely abundant in subtropical low-nutrient regions where they form productivity hotspots. Despite their ecological importance, acantharians remain understudied due to their structural fragility and inability to survive in culture. In order to overcome these challenges and illuminate key aspects of acantharian biology and ecology—including distribution, abundance, and specificity and specialization of symbioses—single-cell RNA sequencing methods were developed for acantharians and used alongside environmental metabarcode sequencing and high-throughput, in-situ imaging. Major findings from this thesis were that i) acantharian cell (> 250 µm) concentrations decrease with depth, which correlates to patterns in relative sequence abundances for acantharian clades with known morphologies but not for those lacking known morphology, and that ii) while individual acantharians simultaneously harbor multiple symbiont species, intra-host symbiont communities do not match environmental communities, providing evidence for multiple uptake events but against continuous symbiont turnover, and that iii) photosynthesis genes are upregulated in symbiotic Phaeocystis​, reflecting enhanced productivity in symbiosis, but DNA replication and cell-cycle genes are downregulated, demonstrating that hosts suppress symbiont cell division. Moreover, storage carbohydrate and lipid biosynthesis and metabolism genes are downregulated in symbiotic ​Phaeocystis​, suggesting fixed carbon is relinquished to acantharian hosts. Gene expression patterns indicate that symbiotic ​Phaeocystis​ is not nutrient limited and likely benefits from host-supplied ammonium and urea, thus providing evidence for nutrient transfer between hosts and symbionts. Interestingly, genes associated with protein kinase signaling pathways that promote cell proliferation are downregulated in symbiotic ​Phaeocystis​. Deactivation of these genes may prevent symbionts from overgrowing hosts and therefore represents a key component of maintaining the symbiosis. This research contributes new insights into the ecologically relevant photosymbioses between Acantharea and ​Phaeocystis​ and illustrates the benefits of combining single-cell sequencing and imaging technologies to illuminate important microbial relationships in marine ecosystems.},
 school = {Okinawa Institute of Science and Technology Graduate University},
 title = {放散虫と共生藻の関係：分布、生息数、特異性、維持支配機構の解明},
 year = {}
}