Examination of changes in parasite population structure when grown in different RBC genotypes and under different O2 conditions. Parasite subpopulations exist as 1N, 2N, or 4N and >4N and in wild-type cells are maintained at ∼ 33%:33%:33%. (A) Represents subpopulations at 1% O2; (B) represents 2N subpopulations at 21% O2. Within the AA genotype, the population structure of growing parasites is almost equally divided between 1N, 2N, and together 4N and >4N. As evident from the graphs, within the AA RBCs, the population structure was similar across both O2 conditions. (A) When grown in AS cells, parasites had a higher percentage of 1N at 1% O2 (46.09% ± 3.84%) and significant reduction in 4N populations as compared with AA (20.479% ± 2.12% in AS vs 31.529% ± 1.73% in AA). For SS RBCs, at 1% O2 (hypoxia), 1N contributes 51.006% ± 4.298% to the population structure, thus explaining the stunted growth at these hypoxic conditions. (B) At 21% O2, 1N, 2N, and 4N of AS changed to 33.09% ± 2.58%, 34.78% ± 0.89%, and 32.27% ± 2.066%, respectively, which is largely similar to the wild-type AA 33%:33%:33% pattern. In SS host cells, parasite subpopulations exhibit a major recovery compared with 1% O2 with 1N, 2N, and 4N at 41.82% ± 3.26%, 33.625% ± 1.829%, and 23.977% ± 1.829%, respectively. None of these at 21% O2 are statistically significant when compared with parasite structures in AA cells. (C) Giemsa-stained images of parasites grown in AA, AS, and SS RBCs at 1% and 21% O2. As evident in representative images, at lower O2 levels, rings (marked with red arrows) were more prevalent in AS and SS cells. As O2 concentrations are increased, parasites grown in AS RBCs appear identical to the parasites in AA RBCs. Parasites grown in SS RBCs also recover and appear similar to the wild type at hyperoxic conditions. Scale = 10 μm.
