Vitamin B12 changes in Nippostrongylus brasiliensis in its free-living and parasitic habitats with biochemical implications.

Bacteria in rat feces cultures that had synthesized vitamin B12 were ingested by the free-living stages of Nippostrongylus brasiliensis and the vitamin was concentrated and stored in the third-stage infective filariform larvae. As assayed with Ochromonas malhamensis, the vitamin B12 content of a single filariform larva as well as the concentration expressed as microgram B12 per g filariform larvae reached extraordinarily high levels, the latter being the highest yet recorded for a metazoan organism. The stored B12 content of the filariforms surviving in fecal culture for as long as 104 days remained constant, whereas the B12 concentration rose due to gradual loss of larval body weight. This storage strategy ensured that a high level of the vitamin would be immediately available to the rapidly growing and differentiating worms following infection of the rat. The changing patterns of B12 content and concentration during the parasitic cycle were followed quantitatively and correlated with B12 turnover, increase in worm weight with growth, and incorporation of B12 into the eggs. The possible sources of B12 and its metabolic functions in nematodes are discussed.