%0 Journal Article
%T Cyanobacteria as an Experimental Platform for Modifying Bacterial and Plant Photosynthesis
%A Dario Leister
%J Frontiers in Bioengineering and Biotechnology
%D 2014
%I Frontiers Media
%R 10.3389/fbioe.2014.00007
%X One of the fascinating characteristics of photosynthesis is its capacity for repair, self-renewal and energy storage within chemical bonds. Given the evolutionary history of plant photosynthesis and the patchwork nature of many of its components, it is safe to assume that the light reactions of plant photosynthesis can be improved by genetic engineering (Leister, 2012). The evolutionary precursor of chloroplasts was a microorganism whose biochemistry was very similar to that of present-day cyanobacteria. Many cyanobacterial species are easy to manipulate genetically and grow robustly in liquid cultures that can be easily scaled up into photobioreactors. Therefore, cyanobacteria such as Synechocystis sp. PCC 6803 (hereafter ˇ°Synechocystisˇ±) have been widely used for decades as model systems to study the principles of photosynthesis (Table 1). Indeed, genetic engineering based on homologous recombination is well established in Synechocystis. Moreover, new genetic engineering toolkits, including marker-less gene deletion and replacement strategies needing only a single transformation step (Viola et al., 2014) and novel approaches for chromosomal integration and expression of synthetic gene operons (Bentley et al., 2014), allow for large-scale replacement and/or integration of dozens of genes in reasonable time frames. This makes Synechocystis a very attractive basis for the experimental modification of important processes like photosynthesis, and it also suggests innovative ways of improving modules of related eukaryotic pathways, among them the combination of cyanobacterial and eukaryotic elements using the tools of synthetic biology. Improving the photosynthetic light reactions in cyanobacteria In plants, the activity of the Calvin cycle (in particular the RuBisCO-mediated carbon fixation step) is considered to represent the major brake on photosynthetic efficiency under saturating irradiance and limiting CO2 concentrations (Quick et al., 1991;Stitt et al., 1991;Furbank et al., 1996). Autotrophic growth of Synechocystis, on the other hand, is constrained by the rate of phosphoglycerate reduction, owing to limitations on the ATP/NADPH supply from the light reactions (Marcus et al., 2011). In fact, cyanobacteria cannot absorb all incoming sunlight due to light reflection, dissipation and shading effects. In some cases, significant numbers of the photons absorbed by the antennae are not used for energy conversion due to dissipation mechanisms. It has therefore been proposed that uneven light distribution could be avoided by using cell cultures with smaller
%K carboxysomes
%K Chloroplasts
%K genetic engineering.
%K Photosynthesis
%K Synechocystis
%K Synthetic Biology
%U http://www.frontiersin.org/Journal/10.3389/fbioe.2014.00007/full