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Himadri B. Pakrasi, Robert G. Kranz, Petra A. Levin, Kathryn G. Miller, Craig S. Pikaard, Ralph S. Quatrano
Date of Award
Restricted Access Dissertation
Doctor of Philosophy (PhD)
Thorough understanding of function in any biological system necessitates accurate information of structure. Cyanobacteria are photosynthetic prokaryotes with three highly differentiated membrane systems: plasma membrane, outer membrane, and an internal system of thylakoid membranes. The presence of different membrane systems lends these cells a unique complexity among bacteria. Many details concerning the interrelations between the membrane systems, and between the membrane systems and other cellular components, are largely unknown. In particular, of outstanding interest is the relationship between the plasma membrane and thylakoid membranes, the organization of thylakoid membranes within the cell, and the identification and association of storage inclusion bodies with the membrane systems. This work addresses these outstanding questions via an analysis of two unicellular cyanobacteria, Synechocystis sp. PCC 6803 and Cyanothece sp. ATCC 51142. While the main focus of this work has been the ultrastructural analysis of these organisms, also described are physiological, genomic, and transcriptomic studies that have been performed in parallel.
Three-dimensional electron microscopy showed that, in Synechocystis , thylakoid membranes are largely arranged as concentric sheets that follow the shape of the plasma membrane. In contrast, thylakoid membranes in Cyanothece are radially arranged, extending from the cell periphery into the cell interior, demonstrating a new type of membrane organization in a cyanobacterium. In both organisms, the thylakoid membranes are a separate system discontinuous from the plasma membrane. While the thylakoid membrane sheets in Synechocystis have been found to be disconnected from each other, in Cyanothece , thylakoid membranes form a network that extends throughout the cell. This Cyanothece thylakoid network is stable throughout the diurnal period, even as adjacent inclusion bodies are accumulated and degraded. The multiple-branching structure by which the thylakoid membrane network is perpetuated throughout the Cyanothece cell suggests that this is a mechanism for thylakoid membrane biogenesis. Furthermore, the thylakoid membrane network has a specific architecture: thylakoids displays a rudimentary helical organization, a potential evolutionary step to the modern grana and stroma thylakoid arrangement in plant chloroplasts. Apparently, each cyanobacterial strain has a unique ultrastructure that facilitates the accomplishment of the many specific metabolic functions required within the same single cell.
Liberton, Michelle, "Membrane Systems in Cyanobacteria" (2008). Retrospective Theses and Dissertations. 19.