In the representative gut bacterium Lactobacillus plantarum, we identified genes encoding the enzymes involved in a saturation metabolism of polyunsaturated fatty acids and revealed in detail the metabolic pathway that generates hydroxy fatty acids, oxo fatty acids, conjugated fatty acids, and partially saturated transfatty acids as intermediates. Furthermore, we observed these intermediates, especially hydroxy fatty acids, in host organs. Levels of hydroxy fatty acids were much higher in specific pathogen-free mice than in germ-free mice, indicating that these fatty acids are generated through polyunsaturated fatty acids metabolism of gastrointestinal microorganisms. These findings suggested that lipid metabolism by gastrointestinal microbes affects the health of the host by modifying fatty acid composition.biohydrogenation | hydratase | fatty acid isomerase | conjugated linoleic acid | lipid nutrition

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We determined the enzymatic characteristics of an industrially important biocatalyst, ␣-ketoglutaratedependent L-isoleucine dioxygenase (IDO), which was found to be the enzyme responsible for the generation of (2S,3R,4S)-4-hydroxyisoleucine in Bacillus thuringiensis 2e2. Depending on the amino acid used as the substrate, IDO catalyzed three different types of oxidation reactions: hydroxylation, dehydrogenation, and sulfoxidation. IDO stereoselectively hydroxylated several hydrophobic aliphatic L-amino acids, as well as L-isoleucine, and produced (S)-3-hydroxy-L-allo-isoleucine, 4-hydroxy-L-leucine, (S)-4-hydroxy-L-norvaline, 4-hydroxy-L-norleucine, and 5-hydroxy-L-norleucine. The IDO reaction product of L-isoleucine, (2S,3R,4S)-4-hydroxyisoleucine, was again reacted with IDO and dehydrogenated into (2S,3R)-2-amino-3-methyl-4-ketopentanoate, which is also a metabolite found in B. thuringiensis 2e2. Interestingly, IDO catalyzed the sulfoxidation of some sulfur-containing L-amino acids and generated L-methionine sulfoxide and L-ethionine sulfoxide. Consequently, the effective production of various modified amino acids would be possible using IDO as the biocatalyst.Hydroxy amino acids are unusual hydroxylated amino acids and are ubiquitous in nature. They exist as secondary metabolites and components of peptides and proteins. Free amino acids are mostly found in higher plants (3,29), and also, free threo-3-hydroxy-L-asparagine has been found in human urine (25) and free 3-hydroxy-