Contributed Talk 2: Less is more: Selective advantages can explain the loss of biosynthetic functions in bacteria

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• D'Souza, G (Max-Planck-Institut fr Chemische kologie)
• Monday 27 October 2014, 15:00-15:15
• Seminar Room 1, Newton Institute.

If you have a question about this talk, please contact Mustapha Amrani.

Understanding Microbial Communities; Function, Structure and Dynamics

Co-authors: Silvio Waschina (Experimental Ecology and Evolution Research Group, Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, 07745 Jena, Germany; Research Group Theoretical Systems Biology, Friedrich Schiller University of Jena, 07743 Jena, Germany), Christoph Kaleta (Research Group Theoretical Systems Biology, Friedrich Schiller University of Jena, 07743 Jena, Germany), Christian Kost (Experimental Ecology and Evolution Research Group, Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, 07745 Jena, Germany)

Bacteria that have adapted to nutrient-rich, stable environments are typically characterized by reduced genomes. The loss of biosynthetic genes frequently renders these lineages auxotroph, hinging their survival on an environmental uptake of certain metabolites. However, the factors that govern this genome streamlining remain poorly understood. Our analysis of 1532 metabolic networks revealed that auxotrophies are likely to be highly prevalent in both symbiotic and free-living bacteria. To unravel whether selective advantages can account for the rampant loss of anabolic genes, we systematically determined the fitness consequences that result from deleting conditionally essential biosynthetic genes from the genome of Escherichia coli in the presence of the focal nutrient. Pairwise competition experiments with each of 16 mutants auxotrophic for different amino acids, vitamins, and nucleobases against the prototrophic wild type unveiled a pronounced, concentration-dependent growth advantage of around 13% for virtually all mutants tested. Our in silico analysis also suggests that bacteria are frequently auxotrophic for multiple metabolites. Also bacteria are frequently subjected to changes in resource environments. Hence we also determined the effect of different carbon environments and epistasis on the fitness of Escherichia coli genotypes from whose genome one, two, or three different amino acid biosynthesis genes have been deleted. Competition experiments between auxotrophic mutants and prototrophic wild type cells in one of two carbon environments revealed that plasticity and epistasis strongly affected the mutants fitness individually and interactively. Taken together, our findings suggest adaptive benefits could drive the loss of conditionally essential biosynthetic genes and that both the genetic background and environmental conditions determine the adaptive value of the loss of these biosynthetic functions.

This talk is part of the Isaac Newton Institute Seminar Series series.

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