HYPER-PRODUCTION OF L-TRYPTOPHAN VIA FERMENTATION WITH CRYSTALLIZATION

A stable and fast L-tryptophan producer, AGX1757, was isolated from Es cherichia coli W3110 trpAE1 trpR tnaA, which carried pSC101-trpI15.14. Cells of AGX1757 did not lose the composite plasmid during fermentati on. Whenever a fed-batch culture of AGX1757 attained an L-tryptophan c oncentration of about 30 g/l, indole began to appear in the broth. The emergence of indole was caused by inhibition of tryptophan synthase d ue to accumulated L-tryptophan. Hence, the production rate Of L-trypto phan sharply decreased. A higher solubility of L-tryptophan in the sup ernatant of culture broth (about 32 g/1) than that in the initial medi um (about 22 g/1) was attributed to some unknown interaction between L -tryptophan and certain macromolecular material(s) coming from the bac terial cells. An addition of non-ionic detergents into the supernatant was effective for decreasing the solubility Of L-tryptophan, hence ca using crystallization Of L-tryptophan. Pluronic L-61 was supplied from outside to an extent of 0.5% in terms of wt% concentration at around 45 h of fermentation when the L-tryptophan accumulated reached about 2 5 g/l. This addition actually caused crystallization Of L-tryptophan a nd, as a result, the inhibitory effect of tryptophan synthase by L-try ptophan accumulated in the broth could be alleviated. Thus far, furthe r fermentation became possible. L-Tryptophan of more than 50 g/l was f inally produced by feeding solutions of both glucose and anthranilic a cid.