Abstract
Bacterial communities may display metabolic complementation, in which different members of the association partially contribute to the same biosynthetic pathway. In this way, the end product of the pathway is synthesized by the community as a whole. However, the emergence and the benefits of such complementation are poorly understood. Herein, we present a simple model to analyze the metabolic interactions among bacteria, including the host in the case of endosymbiotic bacteria. The model considers two cell populations, with both cell types encoding for the same linear biosynthetic pathway. We have found that, for metabolic complementation to emerge as an optimal strategy, both product inhibition and large permeabilities are needed. In the light of these results, we then consider the patterns found in the case of tryptophan biosynthesis in the endosymbiont consortium hosted by the aphid Cinara cedri. Using in-silico computed physicochemical properties of metabolites of this and other biosynthetic pathways, we verified that the splitting point of the pathway corresponds to the most permeable intermediate.
Highlights
Species that coexists on time and space form complex networks of interactions which are shaped by abiotic and biotic factors (Faust and Raes, 2012; Seth and Taga, 2014)
Using the model and the optimization criteria introduced in previous sections, we turn on the analysis of the optimal proteome allocation obtained, for different scenarios
When the metabolites are allowed to permeate, the two cell populations are in principle allowed to interact, and an asymmetric solution corresponding to metabolic complementation may emerge
Summary
Species that coexists on time and space form complex networks of interactions which are shaped by abiotic and biotic factors (Faust and Raes, 2012; Seth and Taga, 2014). The association between different species can be analyzed from the perspective of the metabolic interactions. In this context, the possible nutritional interactions within different organisms can be grouped as follows: (1) competition for limiting nutrients; (2) syntrophy, i.e., the cooperation emerging as each of the partners gain by the metabolic reactions of the other; (3) commensalism or nutrient cross-feeding, in which the presence of an organism that over-produces an essential nutrient enables auxotroph organisms to survive. While in the case of competition one of the organism will inevitably exclude the other (Hardin, 1960), in the cases of syntrophy and cross-feeding, the interaction will tend to stabilize the coexistence of both species, otherwise competitive. When the exchange of nutrients or precursors is bidirectional and is beneficial for both partners, the nutritional interdependence will lead, in most of the cases, to a co-evolutionary process, the most striking example being the emergence of symbiotic associations (Douglas, 1998; Hansen et al, 2007; Germerodt et al, 2016).
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