Plasmid pCGS containing a mutated trp operon was constructed and introduced into an Escherichia coli host for increasing tryptophan biosynthesis. Since tryptophan is a biosynthethic precursor of pyrrolnitrin, the mutated trp operon was inserted into a Pseusdomonas vector pME290 to obtain the plasmid pCG12, and then was introduced into Pseudomonas pyrrocinia for enhancing the pyrrolnitrin synthesis. Data showed that the production of pyrrolnitrin of the transformed strain was five-times greater than that of the parental strain.