Fig. 2. Trypanosomes acidify their environment in liquid culture and on semi-solid agarose plates.

Early procyclic forms (Lister 427 Bern) grown in SDM79 were analysed. a pH (left y-axis) of medium only, a log-phase culture (log, 3.9 × 10⁶ cells ml⁻¹) and a dense culture (dense, 5.6 × 10⁷ cells ml⁻¹). Three technical replicates are shown. The H⁺ concentration is indicated on the right y-axis. Medium only was incubated for the same length of time as the cultures. b, c pH measurements on SoMo plates. b Trypanosomes (2 × 10⁵ cells) were either spotted onto the centre of a plate as a single inoculum (left row) or in pairs (right row). White numbers indicate pH measurements on days 0, 2, 3, 4, and 7 in the centre of a community, at the periphery and in the space between two communities (indicated with a white arrow). c Graphs for pH measurement shown in (b). Each data point represents the pH measured from individual plates (n = 2). Top: plates with single communities. pH at the plate periphery (filled circle, dashed line) or in the centre of the community (filled circle, solid line). Bottom: paired communities. pH at the plate periphery (open circle, dashed line), in the centres of the two communities (filled triangle, solid line), or between them (filled rhombus, dotted line). Y-axes are the same as in (a). d The time-point of migration depends on the volume of the substrate. Equal numbers of early procyclic forms were inoculated onto wells that contained different volumes of medium with agarose. Plates were photographed on days 3, 4, and 5 post-inoculation. Source data are provided as a Source Data file.