S. Azuma et al., HYPER-PRODUCTION OF L-TRYPTOPHAN VIA FERMENTATION WITH CRYSTALLIZATION, Applied microbiology and biotechnology, 39(4-5), 1993, pp. 471-476
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.