Osmoregulation in Enterobacteriaceae: role of proline betaine transport systems

In a wide variety of organisms, L-proIine and glycine betaine are amongst the compounds accumulated intracellularly as compatible solutes to counteract the effects of turgor reduction during growth in water-stressed environments. Two osmoregulatory transport systems, ProP and ProU, have been identified and characterized in the enterobacteria, each of which participates in the active concentration of both L-proline and glycine betaine from the culture medium in response to osmotic stress. The expression of genes encoding the components of the ProU porter is induced 400-fold upon growth in high-osmolarity medium; elucidation of the molecular mechanisms underlying such regulation would possibly enable understanding of the large class of processes that involve transduction of mechanical signals to chemical ones within biological systems. A complete understanding of the molecular basis by which ProP and ProU function in osmoregulation would also provide insight into the mechanisms of similar adaptation at the cellular level in the economically important genera of microbes and higher plants.