Biotechnological Applications of Cyanobacteria: Synechocystis and Synechococcus Strains

Cyanobacteria as phototrophic microorganisms bear great potential for biotechnological application and a truly sustainable bioeconomy. Besides production of biomass and natural compounds, CO₂-based production of diverse value-added compounds with engineered strains enjoys ever-growing interest. Representatives of the genera Synechocystis and Synechococcus are the most used cyanobacterial model organisms for this purpose, with studies ranging from basic research to their utilization as cell factories. For both genera, genetic tools become more and more established, being, however, still far less advanced compared to those available for heterotrophic workhorse strains. Production of CO₂-based compounds, typically established on a proof-of-concept basis, ranges from highly complex products such as pigments, proteins, and hormones to more simple bulk products such as biofuels and commodity chemicals. For some small molecules, e.g., isobutyraldehyde, 2,3-butanediol, L-lactic acid, sucrose, and ethanol, the gram per liter scale has been achieved. The general benefits of cyanobacterial photobiotechnology are the use of light as energy source and the capacity to use CO₂ via photosynthetic carbon fixation. Additionally, the photosynthetic apparatus offers the opportunity to directly utilize electrons derived from photosynthetic water oxidation for redox biotransformations. In this respect, several enzymes have successfully been implemented in cyanobacterial strains, and high specific rates comparable to those achieved with heterotrophs have been reached. Moreover, oxygenic photosynthesis provides an ideal framework to implement oxyfunctionalization reactions also benefitting from the intracellular in situ supply of O₂. This chapter summarizes the recent advances in cyanobacterial biotechnology with a focus on Synechocystis and Synechococcus strains, encompassing both biotransformation reactions and CO₂-based product formation. Additionally, we discuss advantages and limitations of cyanobacterial chassis strains and give perspectives for future research and required measures to establish this unique group of bacteria in industrial biotechnology.