Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

The transcriptional response of freshwater Synechococcus sp. PCC 7942 and oceanic Synechococcus sp. WH 7803 to ammonium, nitrate or iron was studied in single or multiple factor limited cultures. Both strains showed maximum production of NiR mRNA when grown in nitrate-containing media. When grown in ammonium-containing medium, they did not show any signal for NiR mRNA synthesis. The influence on the transcription of NiR mRNA by iron as sole limiting nutrient was also evaluated. Iron increased the NiR mRNA whether or not the positive effect of nitrate was already present. The hybridization signal of mRNA for the large subunit of ribulose bisphosphate carboxylase/oxygenase enzyme (rbcl), was increased in both strains when iron was added. The relative response of NiA was larger than that of rbcL to iron addition. In the final set of experiments, combinations of iron, ammonium, or nitrate nutrient limitation were studied to understand their interactive effect on NiR and rbcL mRNA production. The ammonium-grown cells were allowed to starve for iron and then transferred to +iron+nitrate, +iron-nitrate, or -iron+nitrate cultures. rbcL mANA was increased gradually up to 168 hr. NiR mRNA increased initially but, for unknown reasons, decreased after 24 hr to a minimum that was similar for +iron+nitrate, +iron-nitrate, and -iron+nitrate cultures. A comparison of the rbcL or NiR mRNA from multiple nutrient limitation with that of single nutrient limitation showed different time dependent patterns of synthesis. The response to iron starvation could be different when cells experience a co-limitation with nitrate. This response is also influenced by species specific differences by evolutionary adaptation to different environments. This difference is confirmed in the NiR and rbcL mRNA response in two strains of marine and freshwater Synechococcus for single (iron) or multiple (iron+nitrate) limitation. Physiological studies commonly assume a single factor will constrain cell growth at any moment and when conditions change, the limiting factor will switch. The differential response in the synthesis of NiA and rbcl mANA observed shows that cells exhibit unique responses to combined limitations.

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Cyanobacteria represent one of the morphologically most diverse groups in the bacterial world, and one of the few where true multicellularity evolved. Their diversity ranges from single cells to branched filamentous forms. Some filamentous cyanobacteria are additionally able to undergo cell differentiation forming a two cell type system that represents the simplest model of multicellularity. Anabaena sp. PCC 7120 has been studied extensively in recent years as a model organism. Under nitrogen deprivation it differentiates photosynthetically-active vegetative cells into heterocysts, specialised cells for nitrogen fixation. Accordingly, true multicellularity of nitrogen-fixing cyanobacteria requires different forms of intercellular communication and mutual exchange of nutritional and regulatory compounds. Although several studies could show that molecules are exchanged between cells in Anabaena sp. PCC 7120, little is known about the properties and routes that allow molecules to diffuse between adjacent cells. In this work, the transfer of several physiologically-important molecules was investigated, including the fluorescent sucrose analogue esculin, the fluorescent glucose derivatives 2-NBDG (2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose) and 6-NBDG (6-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-deoxyglucose), and the artificial fluorescent tracer BCECF (2′,7′-Bis-(2-carboxyethyl)-5-(and-6-)carboxyfluorescein). Furthermore, the role of the septal proteins FraC, FraD and SepJ for the exchange of these molecules was examined in Anabaena sp. PCC 7120. Confocal microscopy and fluorescence recovery after photobleaching (FRAP) experiments reveal that cytoplasmic diffusion through channels between neighbouring cells is the primary route for molecular exchange. Loss of FraC, FraD and SepJ strongly reduced the movement of molecules between cells. Overexpression of sepJ altered the heterocyst spacing pattern in Anabaena sp. PCC 7120, suggesting a role of SepJ for the diffusion of regulators. Further, multicellularity in terms of intercellular communication was explored in Mastigocladus laminosus, a true branching cyanobacterium that is one of the morphologically most complex prokaryotes. FRAP analyses indicate the cytoplasmic continuity of the filament network and the dependency of molecular exchange on the morphology of the trichomes.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

published_or_final_version / Biological Sciences / Master / Master of Philosophy

published_or_final_version / Biological Sciences / Master / Master of Philosophy

Bacterial cellulose produced by Gluconacetobacter xylinus possesses an abundance of desirable properties which allow for commercial applications in manufacturing, construction, medicine, as a biofuel feedstock and in electronics as an electrical insulator. Large scale production methods are currently limited by expensive media and requirements for sterile conditions. This thesis investigates the potential for using cellulose synthesized by cyanobacteria as an alternative. Cyanobacteria require fewer media components, fix atmospheric carbon dioxide, and some species fix atmospheric nitrogen, reducing the demand for fertilizer and lowering contamination potential. In this study, a suite of genes involved with cellulose synthesis in G. xylinus were successfully transferred to into the unicellular cyanobacterium, Synechococcus elongatus. Cellulose synthesis was increased in multiple transgenic strains by 300-400% and cellulose microfibrils were observed with enhanced crystallization upon addition of the acsCD transgene from G. xylinus. The evolutionary history of the proteins involved in cellulose synthesis was also investigated, with particular interest paid toward the catalytic subunit. It was determined that all current organisms with the capability of cellulose assembly possess synthases from a single ancestral origin at least 2.5 billion years ago. This work provides additional support to the theory that vascular plants acquired cellulose synthases from cyanobacteria. / text