The synthetic biology toolkit for photosynthetic microorganisms.

Cyanobacteria and algae are photosynthetic microorganisms that are emerging as attractive hosts for synthetic biology applications, ranging from metabolic engineering for the production of industrial biochemicals to microbial energy storage. Photosynthetic microbes have a unique combination of characteristics that drives their consideration for synthetic biology, including relatively simple physiology, fast photosynthetic growth, an availability of model systems, and useful subcellular structures. However, their development as synthetic biology hosts/chassis has been relatively slow compared to that of model heterotrophs. Here we review current synthetic biology tools and applications in photosynthetic microbes and identify opportunities and challenges moving into the future. We focus on cyanobacteria as model photosynthetic prokaryotes, specifically the freshwater unicellular species Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942, the marine unicellular species Synechococcus sp. PCC 7002, and the nitrogen fixing filamentous species Nostoc sp. PCC 7120. Moreover, we present algae as model photosynthetic eukaryotes, specifically the unicellular green alga Chlamydomonas reinhardtii and the diatom Phaeodactylum tricornutum. Finally, we include an examination of some emerging systems. For each organism, the toolbox of genetic parts, high-throughput assembly systems, and other methods that are key components to facilitate synthetic biology are described. Challenges and future directions for synthetic biology and its applications in photosynthetic microorganisms are also discussed.