FIG. 3.

NO₃⁻ reduction by S. putrefaciens with 5 mmol liter⁻¹ NTA (Δ), without NTA (□), with 50 mmol liter⁻¹ goethite (▪), and with 5 mmol liter⁻¹ NTA plus 50 mmol liter⁻¹ goethite (•). Error bars are not shown for cultures lacking goethite, for the sake of clarity.