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Free keywords:
cooperation; gene regulation; interactions; public goods; siderophore; social cheats
Abstract:
The idea that bacteria are social is a popular concept with implications for understanding the ecology and evolution of microbes. The
view arises predominately from reasoning regarding extracellular products, which, it has been argued, can be considered “public
goods.” Among the best studied is pyoverdin—a diffusible iron-chelating agent produced by bacteria of the genus Pseudomonas.
Here we report the de novo evolution of pyoverdin nonproducing mutants, genetically characterize these types and then test the
appropriateness of the sociobiology framework by performing growth and fitness assays in the same environment in which the
nonproducing mutants evolved. Our data draw attention to discordance in the fit between social evolution theory and biological
reality. We show that pyoverdin-defective genotypes can gain advantage by avoiding the cost of production under conditions
where the molecule is not required; in some environments pyoverdin is personalized. By exploring the fitness consequences of
nonproducing types under a range of conditions, we show complex genotype-by-environment interactions with outcomes that
range from social to asocial. Together these findings give reason to question the generality of the conclusion that pyoverdin is a
social trait.
