Abstract
D-amino acids (D-AAs) have various biological activities, such as activation of N-methyl-D-aspartic acid (NMDA) receptor as a co-agonist by D-Ser. Since several free D-AAs are released in the broth monocultured with bacterium and D-AAs are probably utilized for bacterial communication, we presume that intestinal microbiota releases several kinds of free D-AAs, which may be involved in the hosts’ health. However, presently, only four free D-AAs have been found in the ceacal lumen, but not in the colonic lumen. Here, we showed, by simultaneous analysis of chiral AAs using high-sensitivity liquid chromatography-tandem mass spectrometry (LC-MS/MS), that 12 free D-AAs (D-Ala, D-Arg, D-Asp, D-Gln, D-Glu, D-allo-Ile, D-Leu, D-Lys, D-Met, D-Phe, D-Ser, and D-Trp) are produced by intestinal microbiota and identified bacterial groups belonging to Firmicutes as the relevant bacterial candidates.
Highlights
Low-molecular weight metabolites produced by intestinal microbiota from diet- and host-derived compounds regulate intestinal microbiota and host crosstalk[1]
Since several free D-amino acids (D-AAs) are released in the broth monocultured with bacterium[7] and D-AAs are probably utilized for bacterial communication[8,9], we presume that intestinal microbiota releases several kinds of free D-AAs
The concentrations of D-Arg (p < 0.001), D-Asp (p < 0.001), D-Glu (p < 0.001), D-Met (p < 0.001), and D-Trp (p < 0.01) were significantly higher in Ex-GF mice than in GF mice. We demonstrated that these 12 D-AAs are produced by intestinal bacteria, and this is the first report in which free D-Arg, D-Gln, D-allo-Ile, D-Leu, D-Lys, D-Met, D-Phe, D-Ser, and D-Trp were identified in the colonic lumen
Summary
Low-molecular weight metabolites produced by intestinal microbiota from diet- and host-derived compounds regulate intestinal microbiota and host crosstalk[1]. Only one study has analyzed free D-AAs in caecal samples extracted using phosphate buffered saline (PBS) and two-dimensional high-performance liquid chromatography (HPLC) and showed that except the known D-Ala, three additional D-AAs, namely, D-Asp, D-Glu, and D-Pro, were produced by the gut microbiota[13]. This analysis was conducted using only three mice, and is insufficient for profiling of intestinal luminal free D-AAs. Considering that various types of free D-AAs are produced by microorganisms in fermented food[11], four or more free D-AAs could be present in the intestinal lumen, which is inhabited by various bacteria. We observed that 12 free D-AAs are produced by intestinal microbiota and identified the relevant bacterial candidates
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