Osmoprotection of Salmonella enterica serovar Typhimurium by Nγ-acetyldiaminobutyrate, the precursor of the compatible solute ectoine

Nγ-acetyl-2,4-diaminobutyrate (NADA), the precursor of the compatible solute ectoine, was shown to function as an osmoprotectant for the non-halophilic bacterium Salmonella enterica serovar Typhimurium. The addition of NADA-containing extracts of an ectoine synthase mutant of the broad salt-growing halophile Chromohalobacter salexigens DSM 3043T could alleviate the inhibitory effects of high salinity in S. enterica, which lacks the ectoine biosynthetic pathway. NADA, purified from extracts of the mutant, protected S. enterica against salinity stress. This osmoprotective effect was slightly lower than that of ectoine, but more potent than that of hydroxyectoine. Accumulation of purified NADA by S. enterica was demonstrated by 13C-NMR spectroscopy and HPLC analysis. In addition, it was shown that NADA was taken up by S. enterica   via the ProP and ProU transport systems, which are known to transport glycine betaine and proline. This finding provides evidence that these permeases can recognize a diaminoacid that carries an unsubstituted αα-amino group. This is the first time that NADA has been connected with osmoprotective functions in non-halophilic bacteria.