The major long-term goal of this project is to comprehensively identify and analyze all evolutionary mutations that accumulated in five experimentally-evolved strains of the model social bacterium Myxococcus xanthus. Each strain evolved a novel form of social behavior that will be the focus of study, namely obligate cheating, re-evolved multicellular fruiting body development, re-evolved social swarming, adaptive cheater suppression and ten-fold enhanced predatory searching. Having sequenced the genomes of these strains to a high coverage level, all accumulated mutations will be identified by genome sequence, PCR and insertion element analyses. The history of mutation appearances and subsequent frequencies will be defined for each lineage among clones from evolutionary intermediate frozen populations (Specific Aim 1). The mutations that cause the phenotypes of primary interest will be identified, and each mutation will be analyzed for its effects on evolutionary fitness and social phenotypes. The degree of epistatic interaction among sequentially incurred mutations will also be quantified. These goals will be accomplished by transfer of mutations across genomic backgrounds and corresponding population-level performance assays (Specific Aim 2). The molecular pathways and mechanisms that underlie these social adaptations will be characterized by a combination of global approaches (e.g. transcriptome and proteome analysis) and testing of focused mechanistic hypotheses based on existing knowledge of M. xanthus social genetics (Specific Aim 3). This project is highly significant because it represents a ground-breaking, DNA sequence based approach to understanding bacterial social evolution at multiple levels of biological organization. This research investigates several important themes in evolutionary biology that are also relevant to the evolution of human pathogens that rely on social traits analogous to those of M. xanthus for evolutionary success.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Genetic Variation and Evolution Study Section (GVE)
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Eckstrand, Irene A
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Indiana University Bloomington
Schools of Arts and Sciences
United States
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Yu, Yuen-Tsu N; Cooper, Elizabeth; Velicer, Gregory J (2017) A conserved stem of the Myxococcus xanthus sRNA Pxr controls sRNA accumulation and multicellular development. Sci Rep 7:15411
Zee, Peter C; Velicer, Gregory J (2017) Parallel emergence of negative epistasis across experimental lineages. Evolution 71:1088-1095
Kraemer, Susanne A; Wielgoss, S├ębastien; Fiegna, Francesca et al. (2016) The biogeography of kin discrimination across microbial neighbourhoods. Mol Ecol 25:4875-88
Rendueles, Olaya; Zee, Peter C; Dinkelacker, Iris et al. (2015) Rapid and widespread de novo evolution of kin discrimination. Proc Natl Acad Sci U S A 112:9076-81
Mendes-Soares, Helena; Chen, I-Chen Kimberly; Fitzpatrick, Kara et al. (2014) Chimaeric load among sympatric social bacteria increases with genotype richness. Proc Biol Sci 281:
Kraemer, Susanne A; Velicer, Gregory J (2014) Social complementation and growth advantages promote socially defective bacterial isolates. Proc Biol Sci 281:20140036
Chen, I-Chen Kimberly; Griesenauer, Brad; Yu, Yuen-Tsu Nicco et al. (2014) A recent evolutionary origin of a bacterial small RNA that controls multicellular fruiting body development. Mol Phylogenet Evol 73:1-9
Zee, Peter C; Mendes-Soares, Helena; Yu, Yuen-Tsu N et al. (2014) A shift from magnitude to sign epistasis during adaptive evolution of a bacterial social trait. Evolution 68:2701-8
Mendes-Soares, Helena; Velicer, Gregory J (2013) Decomposing predation: testing for parameters that correlate with predatory performance by a social bacterium. Microb Ecol 65:415-23
Manhes, Pauline; Velicer, Gregory J (2011) Experimental evolution of selfish policing in social bacteria. Proc Natl Acad Sci U S A 108:8357-62

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