A multi-stage microbial process for the production of tryptophan is described where the biocatalyst production and bioconversion stages are separated. In the biocatalyst production stage bacterial host cells are transformed with a vector containing a DNA sequence coding for tryptophanase wherein the expression of the tryptophanase gene is directly controllable; the transformed host cells are induced to synthesise tryptophanase; and then in a subsequent bioconversion stage the reaction substrates for tryptophan synthesis are added and the tryptophan which accumulates in the reaction mixture is optionally isolated.
