Regulation of carbon and nitrogen metabolism: adding regulation of ion channels and another second messenger to the mix.

T he regulation of metabolism in bacteria is accomplished by a complex array of signal transduction systems, metabolic interactions, and gene regulatory relationships. For example, maintenance of the balance of carbon and nitrogen metabolism involves (as a partial list) ppGpp, cAMP, the NtrBC two-component system and the coupled Nac-controlled regulon, the leucine-responsive protein LRP, the carbohydrate phosphotransferase system (PTS), and a parallel PTS that has been referred to as the nitrogen PTS. Understanding how these signaling and regulatory systems function to coordinate metabolism remains a significant challenge. In a recent issue of PNAS, Lee et al. (1) show for the first time one of the ways that the nitrogen PTS plays a role in regulating gene expression and metabolism. It does so by regulating an ion channel that is the major K transporter, TrkA. Apparently, K is a second messenger controlling gene expression and enzyme activity in bacteria.