New Assays to Characterise Growth-Related Phenotypes of
Plasmodium falciparum Reveal Variation in Density-Dependent
Growth Inhibition between Parasite Lines
The growth phenotype of asexual blood stage malaria parasites
can influence their virulence and also their ability to survive
and achieve transmission to the next host, but there are few
methods available to characterise parasite growth parameters in
detail. We developed a new assay to measure growth rates at
different starting parasitaemias in a 96-well format and applied
it to characterise the growth of Plasmodium falciparum lines
3D7-A and 3D7-B, previously shown to have different invasion
rates and to use different invasion pathways. Using this simple
and accurate assay we found that 3D7-B is more sensitive to high
initial parasitaemia than 3D7-A. This result indicates that
different parasite lines show variation in their levels of
density-dependent growth inhibition. We also developed a new
assay to compare the duration of the asexual blood cycle between
different parasite lines. The assay is based on the tight
synchronisation of cultures to a 1 h parasite age window and the
subsequent monitoring of schizont bursting and formation of new
rings by flow cytometry. Using this assay we observed
differences in the duration of the asexual blood cycle between
parasite lines 3D7 and HB3. These two new assays will be useful
to characterise variation in growth-related parameters and to
identify growth phenotypes associated with the targeted deletion
of specific genes or with particular genomic, transcriptomic or
proteomic patterns. Furthermore, the identification of
density-dependent growth inhibition as an intrinsic parasite
property that varies between parasite lines expands the
repertoire of measurable growth-related phenotypic traits that
have the potential to influence the outcome of a malarial blood
infection