Figure 3. Growth of pyrimidine auxotrophic T. b. brucei bloodstream forms on various pyrimidine sources.

PYR6-5 ^−/− cell cultures were seeded at a density of 1×10⁵ cells ml⁻¹ and cultured at 37°C/5% CO₂, either in normal HMI-9 or in a simplified pyrimidine version supplemented with dialysed FBS and the indicated pyrimidine source at (A) 100 µM or (B) 1 mM. Samples were taken every 24 h and cell densities determined using a haemocytometer, in duplicate. The experiment shown is representative of several similar experiments with essentially identical results. In cultures with conditions that allowed fast growth, the trypanosome population declined after 36–48 h due to overgrowth.