this invention relates to a process for the enhancement of naphthalene dioxygenase activity in organisms that have been transformed with dna encoding the expression of a multiple component naphthalene dioxygenase enzyme . cells containing the naphthalene dioxygenase enzyme are capable of producing indigo when cultured in the presence of indole . the invention includes procedures to enhance naphthalene dioxygenase activity by transforming a host cell with a dna sequence that encodes at least two ferredoxin polypeptides for each reductase polypeptide and iron - sulfur polypeptide , by growing transformed organisms in the presence of iron , or by transforming a host cell with a dna sequence that encodes a ferredoxin analog .