Intracellular Structures of Normal and Aberrant Plasmodium falciparum Malaria Parasites Imaged by Soft-X-Ray Microscopy

Soft x-ray microscopy is a novel approach for investigation of intracellular organisms and subcellular structures with high spatial resolution. We used x-ray microscopy to investigate structural development of Plasmodium falciparum malaria parasites in normal and genetically abnormal erythrocytes and in infected erythrocytes treated with cysteine protease inhibitors. Investigations in normal red blood cells enabled us to recognize anomalies in parasite structures resulting from growth under unfavorable conditions. X-ray microscopy facilitated detection of newly elaborated structures in the cytosol of fixed, unstained, intact erythrocytes, redistribution of mass (carbon) in infected erythrocytes, and aberrant parasite morphology. In cysteine protease inhibitortreated, infected erythrocytes, high concentrations of material were detected in abnormal digestive vacuoles and aggregated at the parasite plasma membrane. We have demonstrated that an abnormal host erythrocyte skeleton affects structural development of parasites and that this aberrant development can be detected in the following generation when parasites from protein 4.1-deficient red blood cells infect normal erythrocytes. This work extends our current understanding of the relationship between the host erythrocyte membrane and the intraerythrocytic malaria parasite by demonstrating for the first time that constituents of the erythrocyte membrane play a role in normal parasite structural development.