%0 Journal Article %A Fildes, P. %T Production of Tryptophan by Salmonella typhi and Escherichia coli %D 1956 %J Microbiology, %V 15 %N 3 %P 636-642 %@ 1465-2080 %R https://doi.org/10.1099/00221287-15-3-636 %I Microbiology Society, %X SUMMARY: In order to determine whether Salmonella typhi in growth produces free tryptophan in excess, extracts and cultures were tested by various microbiological methods. A positive result was seldom seen, but when excess indole was added to the culture, comparatively large yields of tryptophan were obtained with all strains examined except one in which there was some disability in the indole → tryptophan process. Escherichia coli behaved in the same way, the free tryptophan produced being preserved owing to inhibition of tryptophanase by the indole added. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-15-3-636