Figure 2

¹³C-enrichments of amino acid fragments synthesized from 100% and 50% U-¹³C glucose evidence significant glucose uptake. The 41 measured proteinogenic amino acid fragments in cell hydrolysates of Pt are grouped according to their metabolic precursor(s) (Figure 1). In each of the 100% and 50% U-¹³C glucose ILEs, the fragments show a ¹³C-enrichment approximately proportional to the ¹³C enrichment of the supplied glucose. In contrast, purely photoautotrophic cells would only be ¹³C-enriched to the 1.1% natural abundance CO₂ from the flask headspace. A 2% dilution by initially present biomass and a combination of anaplerotic and photosynthetic inorganic carbon fixation explain the slightly lower average enrichments than would be expected for cells consuming glucose as their sole carbon source: 88% ± 3% in the 100% U-¹³C glucose ILE and 45% ± 1% in the 50% U-¹³C glucose ILE.