VITAMIN-B-12 CHANGES IN NIPPOSTRONGYLUS-BRASILIENSIS IN ITS FREE-LIVING AND PARASITIC HABITATS WITH BIOCHEMICAL IMPLICATIONS

Bacteria in rat feces cultures that had synthesized vitamin B-12 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 B-12 content of a single filariform larva as well as the concentratio n expressed as mu g B-12 per g filariform larvae reached extraordinari ly high levels, the latter being the highest yet recorded for a metazo an organism. The stored B-12 content of the filariforms surviving in f ecal culture for as long as 104 days remained constant, whereas the B- 12 concentration rose due to gradual loss of larval body weight. This storage strategy ensured that a high level of the vitamin would be imm ediately available to the rapidly growing and differentiating worms fo llowing infection of the rat. The changing patterns of B-12 content an d concentration during the parasitic cycle were followed quantitativel y and correlated with B-12 turnover, increase in worm weight with grow th, and incorporation of B-12 into the eggs. The possible sources of B -12 and its metabolic functions in nematodes are discussed.