The production of HCN was determined by spreading 1 ml of J12 broth culture (24 h old) on the King's B plates and by incubating the plates with Whatman filter paper soaked with a solution containing 0.5% picric acid in 2% sodium carbonate placed in the lid plate (Bakker and Schippers 1987). The plates were sealed with the parafilm to avoid gas from escaping. A change in the color, from yellow to orange, of the filter paper was observed after 2 days.