Team:Cornell/project/wetlab/results/nah operon


nah Operon Expression

Biosynthesis of Indigo

Past work indicates that when the nah operon from the NAH7 Pseudomonas plasmid is heterologously expressed in E. coli, the cells have the ability to synthesize indigo from tryptophan [1]. Therefore, as indirect proof that our nah operon BioBrick has activity in our engineered strains, we set several cultures to determine whether indigo was present when cultures were supplemented tryptophan.

E. coli contains the enzyme tryptophanase, which splits the indole group from the peptide backbone. Naphthalene dioxygenase, from the nah operon, then creates a compound which will spontaneously eliminate water and be air oxidized into indigo as the final product.

We are in the process of isolating the four coding regions which make up the naphthalene dioxygenase complex from the operon and BioBrick-ing this genetic part so that future researchers have access an indigo-producing BioBrick.

Testing and Results

Cultures of DH5α containing the nah operon were started in LB broth with 200 μM tryptophan and 100 mg/L ampicillin. Six days after the initial cultures were started, the liquid culture appeared purple. After extracting with chloroform, the organic phase was a light purple color. Testing is being done to determine if this purple compound is indigo.
Fig. 1. Pathway by which E. coli can produce indigo from tryptophan when expressing genes of the Nah7 operon. (Ensley et al., 1983)


[1] Ensley, B., Ratzkin, B., Osslund, T., Simon, M., Wackett, L., & Gibson, D. (1983). Expression of naphthalene oxidation genes in Escherichia coli results in the biosynthesis of indigo. Science, 222(4620), 167-9.