A method for the facile and inexpensive inducible expression of heterologous genes has been discovered. The yhcS regulator gene has been found to be inducible by aromatic carboxylic acids and to alter the expression of operons in the LysR gene family, including the yhcRQP operon, common in enteric bacteria. Heterologous nucleic acid molecules placed under the control of yhcs responsive promoters may be overexpressed in response to the presence of inexpensive aromatic carboxylic acids.