Abstract
The rate of production of methane in many environments depends upon mutualistic interactions between sulfate-reducing bacteria and methanogens. To enhance our understanding of these relationships, we took advantage of the fully sequenced genomes of Desulfovibrio vulgaris and Methanococcus maripaludis to produce and analyze the first multispecies stoichiometric metabolic model. Model results were compared to data on growth of the co-culture on lactate in the absence of sulfate. The model accurately predicted several ecologically relevant characteristics, including the flux of metabolites and the ratio of D. vulgaris to M. maripaludis cells during growth. In addition, the model and our data suggested that it was possible to eliminate formate as an interspecies electron shuttle, but hydrogen transfer was essential for syntrophic growth. Our work demonstrated that reconstructed metabolic networks and stoichiometric models can serve not only to predict metabolic fluxes and growth phenotypes of single organisms, but also to capture growth parameters and community composition of simple bacterial communities.
Highlights
By interacting with other species, organisms are able to occupy environmental niches that they otherwise could not
Mutualisms between tubeworms and methane-oxidizing or sulfide-oxidizing bacteria support life in hydrocarbon seeps in the ocean (Brooks et al, 1987; Cavanaugh et al, 1987); coral–zooxanthella mutualisms drive the growth of corals (Hay et al, 2004); a mutualistic interaction between Archaea and Bacteria is suggested to be responsible for the anaerobic oxidation of methane, an important component of global methane cycles (Boetius et al, 2000)
We explored the practicality of this approach by developing and evaluating a metabolic model for an ecologically relevant microbial mutualism, a syntrophic association between Desulfovibrio vulgaris Hildenborough and Methanococcus maripaludis S2
Summary
By interacting with other species, organisms are able to occupy environmental niches that they otherwise could not. It is the complex web of interactions between species that defines the structure of communities and how those communities respond to environmental change. One form of interspecies interaction that may significantly influence community structure and stability is a mutualism, in which two or more species provide a net benefit to one another (Hay et al, 2004). Mutualisms may be especially important in microbial communities where multiple species are involved in degrading organic substrates (Schink, 2002; Schink and Stams, 2002; Stams et al, 2006).
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