Fig 1.
Carbon and electron transport pathways in M. hungatei.
The methanogenesis pathway has an overall stoichiometry of CO2 + 4 H2 → CH4 + 2 H2O. Substrates and products are indicated with purple and blue ovals, respectively, while reactions with and without estimates are indicated with green and orange arrows, respectively. Metabolite and reaction abbreviations are given in S2 Dataset.
Table 1.
Experimentally observed and computationally predicted extracellular flux distributions for S. fumaroxidans examined in this study.
Fig 2.
Carbon and electron transport pathways in S. fumaroxidans under different substrate conditions.
Simulations maximized ATP production with no minimum biomass requirement. The overall stoichiometry of each pathway corresponds to the experimental stoichiometry given in Table 1. (A) Monoculture growth on fumarate alone. (B) Monoculture growth on fumarate and propionate. (C) Syntrophic growth on propionate. Substrates and products are indicated with purple and blue ovals, respectively, while reactions with and without estimates are indicated with green and orange arrows, respectively. Arrow thickness indicates relative flux values. Metabolite and reaction abbreviations are given in S4 Dataset.
Fig 3.
Alternative carbon and electron transport pathways in S. fumaroxidans under coculture growth conditions.
(A) Formate production via cytFDH. (B) Formate production via cFDH. (A and B) Simulations maximized ATP production with no minimum biomass requirement. The overall stoichiometry of each pathway corresponds to the alternative stoichiometry given in Eq 4. Substrates and products are indicated with purple and blue ovals, respectively, while reactions with and without estimates are indicated with green and orange arrows, respectively. Arrow thickness indicates relative flux values. Metabolite and reaction abbreviations are given in S4 Dataset.
Fig 4.
Predicted individual and community by-product yields in the coculture system at a ratio of three M. hungatei to four S. fumaroxidans.
(A and D) Diagrams illustrating that yields are calculated around individual species (A) and the entire community (D). The plots show the yields of acetate, H2, CO2, and formate for S. fumaroxidans (per propionate) (B and C); CH4 for M. hungatei (per CO2) (B and C); and acetate, H2, CO2, formate, and CH4 for the entire reactor (per propionate) (E and F), as a function of the dilution rate of the reactor (X-axis). Plots are shown in which H2 and CO2 and exchanged (B and E), and in which formate and H2 is exchanged (C and F).
Fig 5.
Predicted community by-product yields by the coculture at a dilution rate of 0.05 days-1.
The plot shows the yields of acetate, H2, CO2, and CH4 for the entire reactor (per propionate) as a function of the relative biomass ratio of M. hungatei to S. fumaroxidans (X-axis). As in Fig 4, formate could be exchanged in the place of CO2 and H2.
Table 2.
Model-predicted steady-state metabolite concentrations for select external metabolites in coculture.