(674d) Constraint-Based Community Modeling Reveals Condition-Dependent Alternate Interactions

Phototrophs and heterotrophs were combined as a novel sustainable symbiotic platform for the production of biofuel precursors. Synthetic communities of cyanobacterium-bacterium and fungus-algae pairs were studied through genome-scale metabolic modeling. Six co-culture metabolic models (CMM) were constructed and used to predict growth phenotypes. The CMM enabled the systematic characterization of communities and the elucidation of the nature of specific interactions between individual members (e.g. mutualism, competition, etc).

The CMM of Chlorella vulgaris and Saccharomyces cerevisiae was reconstructed using the toolbox Constraint-Based Reconstruction and Analysis of Communities, which was developed in the framework of this project. Based on experimental observations, we corroborated our predictions about growth rates, culture medium, and genetic modifications for this co-culture pair. While yeast uptakes O₂ and provides CO₂ when nitrate is the nitrogen source in medium, both members split the available glucose and grow as mutualists. By using the reconstructed CMM, we predicted and validate that when NH₄ was added to the culture medium yeast dominated the co-culture and outcompeted Chlorella, changing the interaction type. The growth of this co-culture is mediated by exchange of ten metabolites; validation by targeted metabolomics is under way. We also evaluated the effect of 1,748 single gene deletions for monocultures and the co-culture. The experimental growth rates match with predictions, e.g. yeast’s mutant alters both Chlorella and yeast growth rates. In some cases, deleting a gene can offer a growth advantage in co-culture, including an improved growth phenotype for the participating species. These examples demonstrate how community metabolic models can accurately predict the behavior of heterogeneous co-culture pairs thus improving production phenotype for bioproduction.