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Adaptation of metabolite leakiness leads to symbiotic chemical exchange and to a resilient microbial ecosystem
Fig 2
Example of leaker-consumer mutualism between two cell species.
(A) A simple example of the mutualism between the leaker (left) and consumer (right) cells. Both have the same network structure that consists of substrate S, enzyme E, ribosome rb, metabolites M1 and M2, and biomass BM, with different rate constants. (B) Schematic illustration of leaker-consumer mutualism. When only a leaker cell is present, the secreted chemical accumulates in the environment and inhibits further secretion (left). The coexistence of other consumer cells is beneficial for both cells as it reduces the concentration of the leaked chemical in the environment (right). (C) Phase diagram of symbiosis depending on 
and 
. Regions M (red), P (green), and NC (black) are delineated by gray lines and represent mutualism, parasitism, and noncoexistence, respectively. The environment volume ratio Venv and the degradation rate in the environment Rdeg are both set at unity. The color denotes the growth rate μ, where a brighter color corresponds to a higher μ. μ with 
is just the growth rate of the leaker cells in isolated conditions, 
; in region M, it is smaller than μ at the corresponding 
value in the panel. (D) Phase diagram of symbiosis depending on the environmental parameters, Rdeg and Venv. The diffusion coefficients of M1 are fixed as 
. Red and black diamonds are delineated by gray lines and represent mutualism and noncoexistence, respectively. The rate constants are set as: 
, so that the leaker’s growth rate in isolation 
with optimal diffusion coefficient 
is higher than the consumer’s growth rate in isolation 
with 
. The other parameters are set as 
.
doi: https://doi.org/10.1371/journal.pcbi.1009143.g002