AUXOTROPHS OF PLASMODIUM-FALCIPARUM DEPENDENT ON P-AMINOBENZOIC ACID FOR GROWTH

The isolation of auxotrophic strains of a parasite offers new opportun ities for studying parasitology. We have isolated cloned lines of Plas modium falciparum that, unlike the parent line from which they were de rived, rely on exogenous p-aminobenzoic acid (PABA) for growth. Isolat ion involved random mutagenesis of a cloned line of P. falciparum and subsequent selection of PABA-dependent parasites. Both parent and PABA -dependent clones were analyzed for PABA uptake and synthesis. Each cl one takes up comparable amounts of PABA from the medium. The parent li ne, clone 3D7, can synthesize PABA de novo, whereas the BABA-dependent clones cannot. The requirement of exogenous PABA for growth by the au xotrophic strains coupled with their inability to synthesize PABA indi cates that normal parasite growth can be completely supported by eithe r synthesis or salvage. This work further clarifies the relationship b etween the availability of PABA and success of the parasite, an issue of debate from classic studies showing reduced parasite load in indivi duals on milk-fed diets.