Figure 1.

Bacterial density in the ascending colon (pLI) is determined by flow and mixing, in addition to bacterial growth. For a range of mixing strengths and flow velocities, average bacterial densities in the ascending colon are shown as a color gradient. If flow through the colon is fast, and mixing weak, the microbiota cannot reach high densities, as they are washed out quickly (bottom right corner of the plot). Both stronger mixing and slower flow rates help to increase microbiota densities. The dashed white lines indicate conditions that we assume to be prevalent in a healthy human colon (a mixing coefficient of 10⁶ µm²/s, see Figure 2 for how this number was derived, and an average flow velocity of 17.5 µm/s). Simulations were performed as described in,¹⁷ Figure S2).