A sustainable, green economy must be created to address global challenges. Nitrogen, the principal component of amino acids and proteins, is currently isolated from the air by the relatively expensive and energy-dependent Haber-Bosch process that converts atmospheric nitrogen into ammonia for the needs of chemical industry and agriculture.
Diazotrophic cyanobacteria, a group of photosynthetic prokaryotes, can naturally fix atmospheric nitrogen, driven by the power of solar energy, and convert it into organic nitrogen-containing compounds. The fixed nitrogen can be deposited in the form of proteins or cyanophycin, also known as CPG (cyanophycin polypeptide granules). Cyanophycin is a non-ribosomally produced amino acid polymer composed of an aspartic acid backbone and arginine side groups. Cyanophycin is insoluble under physiological conditions and is accumulated in the form of granules in the cytoplasm and in heterocysts.
We have developed a methodology for the isolation of CPG over-accumulating mutants of the diazotrophic strain Nostoc sp. PCC 7120 by selecting them on media containing canavanine, a toxic analogue of arginine. We isolated mutant strains accumulating 1.5 to 2-fold more cyanophycin than the wild-type depending on cultivation conditions. The mutant strains demonstrate 30% higher volumetric cyanophycin production in optimal conditions. We sequenced the genomes of the isolated mutants and identified shared and unique mutations in several candidate genes that may be involved in the regulation of cyanophycin accumulation and offer potential targets for genetic manipulation. Overall, we can conclude that we developed a promising platform for the biological conversion of atmospheric nitrogen into a valuable nitrogen-rich compound.
