From Nitrogen to Protein: Harnessing the Power of Nitrogen-Fixing Cyanobacteria for Protein-Rich Biomass Production

To meet the increasing demand for food and protein sources sustainably, innovative dietary alternatives must be explored. Nitrogen-fixing cyanobacteria represent a promising option for producing biomass with high nutritional value while promoting a more efficient and ecofriendly use of nitrogen resources. Most efforts still focus on optimizing the biomass and nutrient content, in terms of total protein, lipid, and carbohydrate composition. However, a systematic investigative approach to how the production system influences the nutritional value of biomass is still lacking. Crucial aspects, such as amino acid profile and bioaccessibility, are typically presented only as a final product characterization. This study presents the diazo-phototrophic continuous cultivation of the heterocystous cyanobacterium Nostoc PCC 7120 as a strategy for the stable production of protein-rich biomass without the need for a nitrogen fertilizer. Findings indicate that light intensity and residence time significantly affect the biomass nutritional value. Production under diazo-phototrophic conditions with a residence time of 1.07 +/- 0.11 days led to a notable increase in the essential amino acid content, which reached 15.06 +/- 0.35%. Considering also the conditionally indispensable amino acids for infant nutrition requirements-arginine, cysteine, and tyrosine-the percentage increased to 23.14 +/- 0.53%. Furthermore, protein bioaccessibility was measured at 81.3 +/- 3.6%, comparable to that of conventional vegetal protein sources like soy. In conclusion, continuous cultivation of Nostoc diazo-phototrophically presents a promising strategy for producing well-balanced biomass from a nutritional perspective, eliminating the need for an external nitrogen fertilizer.