Elevated CO2modulates the metabolic machinery of cyanobacteria and valorizes its potential as a biofertilizer

Elevated CO2 is one of the drivers of global warming and cyanobacteria can be promising options to gainfully convert this to useful biomass. The present investigation was carried out to understand the metabolic changes underlying the C-N dynamics in two cyanobacteria- Anabaena laxa and Calothrix elenkinii grown under ambient CO2 (400 ± 50 ppm) and elevated CO2 (700 ± 50 ppm) environments. Total chlorophyll, phycobilins, proteins, IAA, total sugars, organic carbon, and total-N increased by 14–16% in both the cultures under elevated CO2. Under elevated CO2, the activity of C- and N-assimilation enzymes such as RuBisCO, nitrogenase, nitrate reductase, and glutamine synthetase were significantly enhanced by 20–28% and 18–25% in A. laxa and C. elenkinii respectively. Time course studies suggested that the C-N ratio increased both with the period of incubation and elevated CO2, and there was a significant response of the antioxidant machinery in both organisms. The profiles of fatty acid methyl esters (FAME) analysed using MetaboAnalyst 5.0, illustrated a significant increase in the saturated and branched fatty acids, with increasing age of both cultures, while carbocyclic fatty acids and unsaturated fatty acids enhanced distinctly under elevated CO2 in C. elenkinii and A. laxa respectively illustrating their adaptation and robust nature. Overall, elevated CO2 elicited a positive impact on N-fixation, C-assimilation, and biomass production in both cyanobacteria, thereby improving their suitability as a biofertilizer.