Figure 3

Peptide cross-feeding between Prt⁺ and Prt^- strains in a mixed culture of both variants. The extra cellular protease of Prt⁺ strains cleaves casein into peptides that diffuse away from the cell and can be utilized by invading Prt^- cheating cells (Panel a). Modelling the dynamics between the two variant strains shows that at low cell densities and low Prt⁺ frequencies the fractional gain after one propagation step is high for Prt⁺ cells. If cultures are grown (inoculated) at high cell desities and high frequencies of Prt^- cells the fractional gain of Prt⁺ cells is negative indicating that they are outcompeted by Prt^- cells (Panel b). Reproduced from Bachmann et. al. 2010 with permission from the publisher.