Hyperexpression of the enzyme, parahydroxyphenylpyruvate dioxygenase (pHPPH; melA), in the tyrosine degradative pathway yields excess homogentisic acid which oxidatively polymerizes to pyomelanin. Depression of melA in Shewanella colwelliana strain D was found to result from a single base pair transition upstream of the promoter. This was the sole lesion detected in pHPPH hyperexpressing strains. It is suggested that a T to C transition alters the mRNA structure, exposing the ribosome binding site, thereby enhancing translational efficiency.