Response of Synechocystis sp. PCC 6803 to photoperiod and phosphate alterations using functional proteomics approaches.

The consideration of possible future clean-fuel (H2), biodegradable plastic and potential anticancer drug has made the fresh-water unicellular cyanobacterium, Synechocystis sp. pee 6803 one of the most attractive cyanobacteria strains to commercial and industrial markets. To fully exploit the potential of these natural products, it is essential to understand the cellular response of this organism toward environmental stimulations. In this study, Synechocystis sp. was subjected to qualitative 'shotgun'-based proteomic analysis, and a total of 776 unique proteins, covered 24% of the entire proteome, were successfully identified. The use of Synechocystis sp. as a model of organism also revealed the potential of gel-based prefractionation over more classical chromatography approaches. The reliability of the iTRAQ-mediated quantitative proteomic approach was also assessed using Synechocystis sp., Sulfolobus solfataricus (an Archaea) and Saccharomyces cerevisiae (an Eukaryotes). Based on multiple replicate analyses, biological variation was found to have the greatest impact on results, and thus biological replicates were recommended for inclusion in all future iTRAQ experiments. This investigation also revealed at least ±50% variation is necessary for significant protein expression to have occurred. The functional proteomic approaches in this thesis covered two main fundamental ideas: firstly to investigate the basic cellular response of this organism toward photoperiod (Le. light-dark cycle); secondly, to examine the cellular stress response as a consequence of macronutrient deficiency, specifically phosphate starvation. The cellular response as a result of circadian influence was also studied via combining results from both transcriptomic and proteomic approaches; and possible interactions (e.g. post-translational modification) between mRNA and protein were also discussed.