Figure 1.

Flow scheme for the stable isotope metabolic footprinting approach for marine microalgae. Algal cells are cultured in either ¹²C (control with natural isotopic distribution) or ¹³C-enriched media. Cells are removed by filtration and metabolites in the cell free filtrate concentrated onto solid phase extraction columns. Eluted compounds are then analyzed using FT-ICR mass spectrometry and a novel algorithm is used to automatically locate the stable isotope patterns, compare them to theoretical isotope intensity profiles, and output the empirical formula(e) of the exuded metabolite(s).