Spatial behavioural ecology of the social bacterium Myxococcus xanthus
Final Report Abstract
The work funded by this grant helped to pioneer a new field of understanding the biogeography of both genetic and social phenotype variation in a highly social bacterium. Highlights of what we learned included the following. i) Despite being a highly social bacterium, global natural isolates of Myxococcus xanthus are extremely antagonistic toward one another. In some cases, one strain will exploit another to gain an absolute advantage in sporulation success during multicellular development at the expense of another strain. ii) Global phenotypic variation includes extensive variation in the relationship between population density and sporulation efficiency. While all strains require a minimum density to initiate development, some have a much lower density threshold than others. iii) Global genetic variation in M. xanthus is highly spatially structured, with larger areas harboring more diversity and with more distant populations being more differentiated than neighboring populations. Distant populations appear to diverge by genetic drift. iii) There is a remarkably high degree of genetic variation in this species at the cm scale, but this variation is not spatially structured at the cm scale, indicating that clonal patch size is smaller than 1 cm. iv) Cm-scale populations also vary extensively in swarming rates and patters and secondary metabolite production patterns. v) Cm-scale isolates, even those that show no genetic variation at up to 15 sequenced loci, show frequencies and intensities of antagonism toward one another similar to patterns of antagonism found amond much more divergent and globally distributed isolates. This remarkable result indicates that these incompatibilities evolve at the local scale rather than as a result of divergence of spatially isolated populations. The grant also supported the analysis of developmentally defective social cheater of M. xanthus re-evolved developmental proficiency by a single mutation. This work showed that social bacteria can evolutionarily compensate for social defects by finding alternative regulatory pathways allowing social function and that cheater-resistant cooperators can evolve from cheaters themselves. The re-evolved developmentally proficient cooperator was found to exhibit a very different pattern developmental gene expression than the normal, ancestral cooperator from which the intermediate cheater strain originally derived. Several papers supported by this grant have received attention in the scientific and popular press.
Publications
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2005. Exploitative and hierarchical antagonism in a cooperative bacterium. PLoS Biology 3:1980-1987
Fiegna, F. and G. J. Velicer
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2006. Evolution of an obligate social cheater to a superior cooperator. Nature 441: 310-314
Fiegna, F., Yu, Y.-T. N., Kadam, S. V. and G. J. Velicer
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2006. Genetic population structure of the soil bacterium Myxococcus xanthus at the centimeter scale. Applied & Environmental Microbiology 72: 3615-3625
Vos, M. and G. J. Velicer
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2006. Variable patterns of density-dependent survival in a social bacterium. Behavioral Ecology, 17:833-838
Kadam, S. V. and G. J. Velicer
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2008. Discovering the hidden secondary metabolome of Myxococcus xanthus: a study of intra-specific diversity. Applied and Environmental Microbiology, 74:3058-3068
Krug, D., G. Zurek, O. Revermann, M. Vos, G. J. Velicer and R. Müller
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2008. Isolation by distance in the spore-forming soil bacterium Myxococcus xanthus. Current Biology, 18:386-391
Vos, M. and G. J. Velicer
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2008. Natural variation of gliding motility in a centimetre-scale population of Myxococcus xanthus. FEMS Microbiology Ecology, 64:343-350
Vos, M. and G. J. Velicer
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2008. Novel transcriptome patterns accompany evolutionary reversion of defective social development in the bacterium Myxococcus xanthus. Molecular Biology and Evolution, 25:1274-1281
Kadam, S. V., J. S. Jakobson, L. Sogaard-Andersen and G. J. Velicer
