title: Less is more: selective advantages can explain the prevalent loss of biosynthetic genes in bacteria.
abstract: 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. The evolutionary forces that drive this genome degradation, however, remain elusive. Our analysis of 949 metabolic networks revealed auxotrophies are likely 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 genomes of Escherichia coli and Acinetobacter baylyi in the presence of the focal nutrient. Pairwise competition experiments with each of 20 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. Individually deleting different genes from the same biosynthesis pathway entailed gene-specific fitness consequences and loss of the same biosynthetic genes from the genomes of E. coli and A. baylyi differentially affected the fitness of the resulting auxotrophic mutants. Taken together, our findings suggest adaptive benefits could drive the loss of conditionally essential biosynthetic genes.
authors.affiliation: Experimental Ecology and Evolution Research Group, Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, 07745, Jena, Germany.
authors.forename: Glen
authors.initials: G
authors.lastname: D'Souza
authors.forename: Silvio
authors.initials: S
authors.lastname: Waschina
authors.forename: Samay
authors.initials: S
authors.lastname: Pande
authors.forename: Katrin
authors.initials: K
authors.lastname: Bohl
authors.forename: Christoph
authors.initials: C
authors.lastname: Kaleta
authors.forename: Christian
authors.initials: C
authors.lastname: Kost
mesh_terms: D000150:Acinetobacter / Q000235:genetics* / Q000378:metabolism*; D001419:Bacteria / Q000235:genetics* / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D005798:Genes, Bacterial / Q000235:genetics; D020043:Genes, Essential; D053858:Metabolic Networks and Pathways / Q000235:genetics*
keywords: Adaptive gene loss; auxotrophy; black queen hypothesis; cross-feeding; prototrophy; symbiosis