Extracellular substrate and metabolite concentrations in pure and mixed cultures. Glutamine, glutamate and glucose were quantified by an enzymatic assay. Gluconate and 2-KDG were quantified by HPLC. Time courses of (A) glutamine (filled symbols) and glutamate (open symbols) and (B) glucose (half-filled symbols), 2-KDG (filled symbols) and gluconate (open symbols) are presented over a cultivation period of 12 h. For S. aureus neither gluconate nor 2-KDG were detected (n.d., below detection limit). Error bars represent standard deviation of three biological replicates.