Cyanophycin—an Ideal Bacterial Nitrogen Storage Material with Unique Chemical Properties

Abstract

Cyanophycin (CGP) is a nitrogen-rich, polypeptide-like storage material of cyanobacteria and heterotrophic bacteria. CGP inclusions were discovered more than 100 years ago and from that time on have attracted the interest of many researchers with both basic and applied research interests. The discovery of CGP goes along with the de- velopment of the light microscope and the electron microscope, respectively, as well as application of differential staining techniques and refined analysis methods that were employed to determine its chemical structure. CGP has different physiological functions depending on the cell type and organism in which it occurs, but can be considered as a widespread intracellular nitrogen reserve. Its biosynthesis is mediated by the activity of a single enzyme, the cyanophycin synthetase, that possesses two putative active sites re- sponsible for the alternating incorporation of the amino acids arginine and aspartic acid. Heterologous expression of CGP synthetase genes (cphA) and the activity of the enzyme during in vitro studies led to the formation of CGP with altered monomer composi- tion. By employment of recombinant bacterial strains that accumulate large amounts of CGP, strategies were developed to produce CGP in semitechnical amounts in comparably cost effective and time saving biotechnological processes. CGP inclusion body formation in transgenic plant lines demonstrated the potential of eukaryotic organisms to serve as hosts for heterologous expression of cphA and as potential future CGP production organisms.