title: The evolution of bacterial cell size: the internal diffusion-constraint hypothesis.
abstract: Size is one of the most important biological traits influencing organismal ecology and evolution. However, we know little about the drivers of body size evolution in unicellulars. A long-term evolution experiment (Lenski's LTEE) in which Escherichia coli adapts to a simple glucose medium has shown that not only the growth rate and the fitness of the bacterium increase over time but also its cell size. This increase in size contradicts prominent 'external diffusion' theory (EDC) predicting that cell size should have evolved toward smaller cells. Among several scenarios, we propose and test an alternative 'internal diffusion-constraint' (IDC) hypothesis for cell size evolution. A change in cell volume affects metabolite concentrations in the cytoplasm. The IDC states that a higher metabolism can be achieved by a reduction in the molecular traffic time inside of the cell, by increasing its volume. To test this hypothesis, we studied a population from the LTEE. We show that bigger cells with greater growth and CO2production rates and lower mass-to-volume ratio were selected over time in the LTEE. These results are consistent with the IDC hypothesis. This novel hypothesis offers a promising approach for understanding the evolutionary constraints on cell size.
authors.affiliation: CEFE UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, Montpellier Cedex 5, France.|UMR-BGPI-INRA-TA A-54/K Campus International de Baillarguet, Montpellier Cedex 5, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Gallet
authors.affiliation: CEFE UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, Montpellier Cedex 5, France.
authors.forename: Cyrille
authors.initials: C
authors.lastname: Violle
authors.affiliation: CEFE UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, Montpellier Cedex 5, France.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Fromin
authors.affiliation: CEFE UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, Montpellier Cedex 5, France.
authors.forename: Roula
authors.initials: R
authors.lastname: Jabbour-Zahab
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA.|Santa Fe Institute, Santa Fe, NM, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Enquist
authors.affiliation: CEFE UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE, Montpellier Cedex 5, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lenormand
mesh_terms: D001419:Bacteria / Q000166:cytology* / Q000235:genetics*; D005075:Biological Evolution; D048429:Cell Size