Beta-aminoglutaric acid is a major soluble component of Methanococcus thermolithotrophicus

13C- and 15N-NMR spectroscopy have been used to identify beta-aminoglutaric acid (beta-glutamic) as a major soluble component of the thermophilic, autotrophic marine methanogen Methanococcus thermolithotrophicus. This rare, non-protein amino acid has been recognized as a major dissolved free amino acid in marine sediments, but the microorganism responsible for its production has not previously been identified. The concentration of beta-aminoglutarate (beta-glutamate) is about one half that of free alpha-glutamate and increases (relative to the alpha-isomer) as cells enter the stationary phase. Analysis of the 13C label distribution in a 13CO2-pulse/12CO2-chase experiment shows that label enters the beta-aminoglutarate pool after it has decayed from other small soluble molecules. This implies that beta-aminoglutarate is a catabolic product of the cells. Preliminary biosynthesis studies with labeled precursors indicate that only a single acetate moiety is incorporated in this unusual compound. This information is used to suggest possible biosynthetic pathways.