GC-MS analysis of diaminopimelic acid stereoisomers and amino acid enantiomers in rumen bacteria

The amounts and the configuration of the stereoisomers of 2,6-diaminopimeli c acid (Dap) and the enantiomeric content of other amino acids were determi ned in five individual species (Fibrobacter succinogenes, Streptococcus bov is, Selenomonas ruminantium, Prevotella ruminicola and Anaerovibrio lipolyt ica) of rumen bacteria, and in samples of mixed rumen bacteria isolated fro m sheep. The separation and quantification of the Dap stereoisomers was ach ieved by gas chromatography (GC) of trifluoroacetyl 2-propyl esters on a Ch irasil-L-Val fused silica column, and detection was achieved by selected io n monitoring mass spectrometry (SIM-MS). No isomers of Dap were detected in S. bovis and P. ruminicola, two of the bacterial isolates. LL- and DD-Dap were not detected in any of the bacterial samples. As only the meso-isomer of Dap was detected in these microorganisms, it was quantified by adding LL -Dap as an internal standard before the bacteria were acid-hydrolyzed. Amou nts of between 4.8 and 12.0 mg meso-Dap per gram of bacterial dry matter (D M) were determined. The presence in the rumen bacteria of free amino acid e nantiomers, extractable with 70% aqueous ethanol, were determined by GC-SIM -MS; the D-amino acids were predominantly Ala, Asp and Glu, but there was c onsiderable variation between the species. Copyright (C) 1999 John Wiley & Sons, Ltd.