¹⁵N₂ and ¹³CO₂ fixation by cyanobacteria as measured by Raman and isotope ratio mass spectrometry. (A) Single-cell Raman spectra of Anabaena sp. PCC 7120 incubated with ¹⁵N₂ at various headspace percentages. (B) A comparison of single-cell Raman spectra of Anabaena sp. PCC 7120 and R. raciborskii XM1 incubated in the air (¹⁴N₂) and ¹⁵N₂ of 99.36%, respectively. (C) The linear correlation between ¹⁵N₂ percentages in the headspace and PCA scores derived from ¹⁵N-induced spectral variations of Anabaena sp. PCC 7120. Each point is from a single-cell, and ∼20 cells were measured. A significant difference was observed between 0.36 and 10.22% of ¹⁵N₂ in the headspace (P < 0.001, t-test). (D) The linear correlation between PCA scores and bulk ¹⁵N contents of Anabaena sp. PCC 7120 measured via isotope ratio mass spectrometry. (E) Single-cell Raman spectra of Anabaena sp. PCC 7120 incubated in ¹³C-NaHCO₃-amended media. (F) A comparison of single-cell Raman spectra of Anabaena sp. PCC 7120 and R. raciborskii XM1 incubated in ¹²C-NaHCO₃ and ¹³C-NaHCO₃ at 99.36%. (G) The linear correlation between ¹³C-NaHCO₃ percentages in the incubation medium and PCA scores derived from ¹³C-induced spectral variations of Anabaena sp. PCC 7120. Each point is from a single-cell. A significant difference was observed between 1.11 and 10.90% of ¹³C in the medium (P < 0.001, t-test). (H) The linear correlation between PCA scores and bulk ¹³C contents of Anabaena sp. PCC 7120 was measured via isotope ratio mass spectroscopy.