Chemical characterization of an antimicrobial substance produced by Lactobacillus reuteri

Lactobacillus reuteri converts glycerol into a potent cell growth inhibitor. This substance, termed reuterin, inhibits the growth of gram-positive and gram-negative bacteria as well as yeasts, fungi, and protozoa. Semipreparative chromatography was used to purify reuterin, and Fourier transform infrared spectroscopy and liquid chromatography-mass spectrometry were used to establish the molecular weight as well as the molecular functionality of the reuterin molecule. Nuclear magnetic resonance studies of purified reuterin carried out with deuterium oxide confirmed the presence of two three-carbon compounds, beta-hydroxypropionaldehyde and the corresponding hydrated acetal, and a six-carbon cyclic dimer of the aldehyde. Further nuclear magnetic resonance studies with deuterated methanol revealed that in this solvent the compound existed as a three-carbon compound in a methoxy form. Trimethylsilyl derivatives of reuterin were analyzed by gas chromatography-mass spectrometry, and a molecule was identified which had a molecular weight corresponding to a disilylated dimeric structure. On the basis of the above information, reuterin was determined to be an equilibrium mixture of monomeric, hydrated monomeric, and cyclic dimeric forms of beta-hydroxypropionaldehyde. This was subsequently confirmed by chemical synthesis.