FIG 2.

Relationship of ABM production and intracellular free-thiol amino acids of WT S. griseus. (A) Bioassay with cells grown in the absence (APB-iron) or presence (APB) of 1 mM iron in a glycerol-based ABM production medium (APB). The size of the inhibition zone is proportional to the amount of ABM in the culture assayed (see Materials and Methods). (B) HPLC-fluorescence detection of monobromobimane-derived intracellular amino acids. Cysteine (●) and homocysteine (*) are the only two free-thiol amino acids detected under these conditions. The chromatograms show (i) and (ii) standards, (iii) N-ethylmaleimide (NEM)-treated intracellular metabolic extracts (the negative control), (iv) cells in APB without iron, (v) cells in normal APB with 1 mM iron, and (vi) cells in APB supplemented with 9 mM propargylglycine (APB+PPGL). Percentage ratios of the peak areas of the two thiols are shown for traces iv, v, and vi. The standard error of three replicates for each was ≤0.2. (C) ABM production of cells grown in APB or APB+PPGL. ABM was quantified by isolation and HPLC analysis. The statistical significance was derived from nine experimental replicates; the standard error is presented by an error bar. **, P < 0.01 (t test).