Abstract

Co-authors: Glen D’Souza (Experimental Ecology and Evolution Research Group, Max Planck Institute for Chemical Ecology), Christian Kost (Experimental Ecology and Evolution Research Group, Max Planck Institute for Chemical Ecology), Christoph Kaleta (Theoretical Systems Biology Research Group, FSU Jena)

Bacteria invest a significant proportion of their available energy and resources into the biosynthesis of amino acids, which are required for cell growth and maintenance. As a consequence, the costs of amino acid biosynthesis profoundly limit the growth rate and, hence, the fitness of a bacterial species. Despite the substantial role for the metabolic economics of a cell, little is known about how these costs may shape the dynamics of cooperative cross-feeding interactions in bacterial communities. Here we show that the growth rates of Escherichia coli amino acid auxotrophic strains relative to the growth rate of the E. coli wild type are strongly carbon source-dependent, when amino acid availability is limiting. To understand these differences we developed a computational framework to quantitatively estimate biosynthetic costs of amino acid anabolism. This approach is based on a genome-scale metabolic network of E. coli and essentially estimates the amount of a given carbon source which is needed to synthesize a specific amino acid. The observed carbon source-dependent increase of the auxotroph’s maximum growth rate max with increasing amino acid concentration correlated positively with the predicted biosynthetic costs. We conclude that the differences in the increase of max are due to the metabolic costs, which the auxotrophs save by taking up the focal amino acid from the environment. These findings imply that there is a high potential for mutualistic amino acid cross-feeding interactions to evolve among sympatric populations of the same bacterial species that specialize in the utilization of different substrates when multiple carbon sources are available in the environment.