BIOSYNTHETIC PATHWAYS OF THE OSMOLYTES N-EPSILON-ACETYL-BETA-LYSINE, BETA-GLUTAMINE, AND BETAINE IN METHANOHALOPHILUS STRAIN FDF1 SUGGESTED BY NUCLEAR-MAGNETIC-RESONANCE ANALYSES

Methanohalophilus strain FDF1 synthesizes beta-glutamine, betaine, and Nepsilon-acetyl-beta-lysine as osmoprotective agents when the cells are grown in high external concentrations of NaCl. Nuclear magnetic resonance spectroscopic analyses of (CH3OH-CO2)-C-13-C-12 label incorporation by the cells provide information on the biosynthetic pathways of these organic osmolytes. The labeling studies indicate that Methanohalophilus strain FDF1 produces glutamate and beta-glutamine via a partial oxidative Krebs pathway. C-13 labeling of betaine is consistent with methylation of glycine generated from serine (via serine hydroxymethyltransferase). The labeling pattern for Nepsilon-acetyl-beta-lysine is consistent with the synthesis of its precursor alpha-lysine occurring by the diaminopimelate pathway in these cells.