Origin of D-alanine present in urine of mutant mice lacking D-amino-acid oxidase activity

Abstract

Urine of mutant ddY/DAO- mice lacking D-amino-acid oxidase contained 13 times more D-alanine than that of normal ddY/DAO+ mice. Because D-alanine is a component of bacterial cell walls, the possibility that the urinary D-alanine came from intestinal bacteria was examined. In ddY/DAO- mice that were made germ free at birth and reared in a germ-free environment, the quantity of urinary D-alanine was found to be at a low level comparable to that of the normal mice. When these germ-free mice were made gnotobiotic by inoculation with gram-negative bacteria (Escherichia coli and Bacteroides vulgatus), the urinary D-alanine increased to a high level. When these gnotobiotic mice were further inoculated with gram-positive bacteria (Bifidobacterium longum and Eubacterium aerofaciens), the urinary D-alanine increased further. These results indicate that most of the urinary D-alanine of the conventionally reared ddY/DAO- mice is of gastrointestinal bacterial origin.