Genome Editing in Cyanobacteria

Cyanobacteria are potential organisms being exploited for a wide range of biotechnological applications. They are photosynthetic bacteria and grow in a carbonfree medium and become attractive hosts for biotechnology industries. Cyanobacteria can utilize solar energy and atmospheric CO2 for the growth and synthesis of biomolecules. It is used in many large-scale preparations of various bioproducts such as pharmaceuticals, biofuels, etc. Cyanobacteria become target organisms for the next generation of biofactories for producing desired products with a low-cost technology. The problem in the metabolic engineering of Cyanobacteria is due to ploidy. It has multiple copies of chromosomes ranging from 3-218 copies. There are 12 copies of the genome in Synechocystis PCC 6803 and 3 copies in Synechococcus PCC 7942. Segregation analysis in the conventional genetic approaches of Cyanobacteria becomes laborious due to its polyploidy. Modern genome editing tools such as CRISPR-Cas9 and 12 are available to perform genome editing. CRISPR-Cas9 has been used in a wide range of Cyanobacteria such as Synechococcus elongates UTEX 2973, Synechocystis sp. PCC 6803. To avoid toxic effects caused by Cas-9, a low-level expression system is adopted in Cyanobacteria. Cas-9 base genome editing was applied in Synechococcus and produced succinate 11-fold higher than the normal. Cas-9 is used to cure plasmids in Synechocystis sp. PCC 6803 to develop a shuttle vector for heterologous expression. Another variant of genome editing tool is CRISPR-Cas12a, which is successfully used in Synechocystis sp.