Thesis (M.S.)--Indiana University, 2007. / Title from screen (viewed on Apr. 30, 2007) Department of Geography, Indiana University-Purdue University Indianapolis (IUPUI) Includes vita. Includes bibliographical references (leaves 122-125)

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Thesis (M.A.)--York University, 2007. Graduate Programme in Geography. / Typescript. Includes bibliographical references (leaves 112-121). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38799

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph.D.)(Microbiology))--University of Pretoria, 2009. / Includes English summary. Includes bibliographical references.

Thesis (Ph.D.)--City University of Hong Kong, 2005. / "Submitted to Department of Biology and Chemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2011. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Several genera of cyanobacteria produce microcystin, a monocyclic peptide, with a unique chemical structure. To date, there have been over a 100 different structural variants of microcystin which have been identified. Microcystin production is affected by numerous environmental factors. However, the primary modulating factor for intracellular microcystin quota is the intracellular N:C ratio. No clearly defined biological role has been described for microcystin. Proposed roles for microcystin include defence against plankton grazers, metal chelation, an infochemical and a protectant against oxidative stress. There is sufficient evidence to support a biological role for microcystin in photosynthesis: microcystin is predominantly located in the thylakoid membranes, the microcystin gene cluster is differentially expressed as a function of light and a growth advantage for the microcystin producer in saturating light intensities. The purpose of this study is to investigate a possible biological role for microcystin in preventing photoinhibition and thus explaining the growth advantage observed in toxin-producers over non-toxin-producers. The uptake of exogenous microcystin was observed in Synechocystis PCC 6803 which was internalized and located in the thylakoid membranes and caused the inhibition of photosynthesis. Microcystin variants and increasing concentrations of microcystin-LR had no effect on the fluidity of the thylakoid membranes. The exposure of thylakoid membranes from Synechocystis PCC 6803 to physiologically relevant concentrations of different microcystin variants resulted in the inhibition of photosystem II activity but not photosystem I activity. The inhibition of photosystem II was variant dependent and concentration dependent for microcystin-LR and microcystin-RR. Chlorophyll a fluorescence data showed that photosystem II inhibition was caused by the inhibition of the oxygen evolving complex. Furthermore, a completion study revealed that the microcystin-producing Microcystis PCC 7806 had a competitive advantage over the non-microcystin producing ΔmcyA mutant of Microcystis PCC 7806 at high light intensities. The data indicates that microcystin protects the toxin-producer by either retarding or preventing photoinhibition and thus identifying the first data supported function for microcystin in cyanobacteria.

Graduation date: 2003