Quantitative Dissection of Clone-Specific Growth Rates in Cultured Malaria Parasites

Measurement of parasite proliferation in cultured red blood cells underpins many facets of malaria research, from drug sensitivity assays to assessing the impact of experimentally altered genes on parasite growth, virulence, and fitness. Pioneering efforts to grow Plasmodium falciparum in cultured red blood cells revolutionized malaria research and spurred the development of semi-high throughput growth assays using radio-labeled hypoxanthine, an essential nucleic acid precursor, as a reporter of whole-cycle proliferation (Trager and Jensen, 1976; Desjardins et al., 1979). Use of hypoxanthine (Hx) and other surrogate readouts of whole-cycle proliferation remains the dominant choice in malaria research. While amenable to high-throughput inference of bulk proliferation rates, these assays are blind to the underlying developmental and cellular steps of growth in human red blood cells. Modern whole-genome methods promise to reveal much about basic parasite biology, but progress is hindered by limitations of our ability to precisely quantify the specific development and growth events within the erythrocytic cycle. Here we build on standard visual and Hx-incorporation measures of growth by quantifying sub-phenotypes of a rapid proliferator, the multi-drug resistant clone Dd2, from a standard wild type clone, HB3. These data illustrate differences in cycle duration, merozoite production, and invasion rate and efficiency that underpin Dd2’s average 2-fold proliferation advantage over HB3 per erythrocytic cycle. The ability to measure refined growth phenotypes can inform the development of high-throughput methods to isolate molecular and developmental determinants of differential parasite growth rates