The maintenance and significance of the complex populations of microbe
s present in the mammalian intestine are poorly understood. Comparison
of conventionally housed and germ-free NMRI mice revealed that produc
tion of fucosylated glycoconjugates and an alpha 1,2-fucosyltransferas
e messenger RNA in the small-intestinal epithelium requires the normal
microflora. Colonization of germ-free mice with Bacteroides thetaiota
dmicron, a component of this flora, restored the fucosylation program,
whereas an isogenic strain carrying a transposon insertion that disru
pts its ability to use L-fucose as a carbon source did not. Simplified
models such as this should aid the study of open microbial ecosystems
.