Nostoc

Nostoc is a genus of filamentous cyanobacteria, the blue-green algae, that grow in damp places as distinctive green to black gelatinous colonies. These organisms fix atmospheric nitrogen through specialized heterocyst cells and produce abundant polysaccharide slime. Certain species synthesize large amounts of phycobiliproteins, the vivid blue and red accessory pigments eyed as natural alternatives to synthetic food colours. Several Nostoc species are traditional foods in Asia and the Andes, eaten for their protein and polysaccharide content. Commercial use demands careful strain selection and closed cultivation, because wild cyanobacterial mats can harbour toxin producers; photobioreactors plus toxin screening make food applications feasible.