air saturation l tryptophan is fed to produce indigo the l tryptophan is first converted to indole by the action of the enzyme tryptophanase encoded on the chromosome of fm5 the indole is then converted to indigo by the action of the naphthalene dioxygenase enzyme system encoded by the plasmid borne genes up to 20 g l indigo can be produced by such a process an indigo containing fermentation broth with 12 0 g l indigo and 147 g l total solids 8 2 indigo purity made such as described in example 2 was recovered as shown in fig2 indigo purity after the various steps is summarized in table 1 an initial centrifugation was attempted to specifically separate indigo from cell mass but no separation was observed the material was resuspended in water to 14 0 g l indigo and naoh was added to a final concentration of 1 this was held for 12 hours at 15 u00b0 c after being passed through a centrifuge the resulting sludge contained 158 g l indigo and 232 g l total solids for an indigo purity of 68 an increase of a factor of eight water and naoh were added to give 115 g l indigo and 5 naoh and the mixture was heated to 90 u00b0 c and held for 12 hours centrifugation was followed by resuspension to the original volume with water and a second centrifugation the resulting sludge had 366 g l indigo and 401 g l total.