An osmoregulated dipeptide in stressed Rhizobium meliloti.

One common mechanism of cellular adaptation to osmotic stress is the accumulation of organic solutes in the cytosol. We have used natural-abundance 13C nuclear magnetic resonance to identify all organic solutes that accumulate to significant levels in Rhizobium meliloti. Our studies led to the discovery of a new dipeptide, N-acetylglutaminylglutamine amide (NAGGN), which is accumulated during osmotic stress. Only rarely have peptides been shown to function in bacteria, and furthermore, this is the first example of a peptide playing a role in osmoregulation. Evidence for the biological role of NAGGN in osmotic-stress protection is presented.