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Natural variation in developmental life-history traits of the bacterium Myxococcus xanthus.

ABSTRACT: The soil bacterium Myxococcus xanthus is a model for the study of cooperative microbial behaviours such as social motility and fruiting body formation. Several M. xanthus developmental traits that are frequently quantified for laboratory strains are likely to be significant components of fitness in natural populations, yet little is known about the degree to which such traits vary in the wild and may therefore be subject to natural selection. Here, we have tested whether several key M. xanthus developmental life-history traits have diverged significantly among strains both from globally distant origins and from within a sympatric, centimetre-scale population. The isolates examined here were found to vary considerably, in a heritable manner, in their rate of developmental aggregation and in both their rate and efficiency of spore production. Isolates also varied in the nutrient-concentration threshold triggering spore formation and in the heat resistance of spores. The large diversity of developmental phenotypes documented here leads to questions regarding the relative roles of selection and genetic drift in shaping the diversity of local soil populations with respect to these developmental traits. It also raises the question of whether fitness in the wild is largely determined by traits that are expressed independent of social context or by behaviours that are expressed only in genetically heterogeneous social groups.

SUBMITTER: Kraemer SA

PROVIDER: S-EPMC2910118 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Natural variation in developmental life-history traits of the bacterium Myxococcus xanthus.

Kraemer Susanne A SA Toups Melissa A MA Velicer Gregory J GJ

FEMS microbiology ecology 20100414 2

The soil bacterium Myxococcus xanthus is a model for the study of cooperative microbial behaviours such as social motility and fruiting body formation. Several M. xanthus developmental traits that are frequently quantified for laboratory strains are likely to be significant components of fitness in natural populations, yet little is known about the degree to which such traits vary in the wild and may therefore be subject to natural selection. Here, we have tested whether several key M. xanthus d ...[more]

PMID: 20491924

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Project description:The ability of plants to acquire and use water is critical in determining life-history traits such as growth, flowering, and allocation of biomass into reproduction. In this context, a combination of functionally linked traits is essential for plants to respond to environmental changes in a coordinated fashion to maximize resource use efficiency. We analyzed different water-use traits in Arabidopsis ecotypes to identify functionally linked traits that determine water use and plant growth performance. Water-use traits measured were (i) leaf-level water-use efficiency (WUE i ) to evaluate the amount of CO 2 fixed relative to water loss per leaf area and (ii) short-term plant water use at the vegetative stage (VWU) as a measure of whole-plant transpiration. Previously observed phenotypic variance in VWU, WUE i and life-history parameters, highlighted C24 as a valuable ecotype that combined drought tolerance, preferential reproductive biomass allocation, high WUE i , and reduced water use. We therefore screened 35 Arabidopsis ecotypes for these parameters, in order to assess whether the phenotypic combinations observed in C24 existed more widely within Arabidopsis ecotypes. All parameters were measured on a short dehydration cycle. A segmented regression analysis was carried out to evaluate the plasticity of the drought response and identified the breakpoint as a reliable measure of drought sensitivity. VWU was largely dependent on rosette area, but importantly the drought sensitivity and plasticity measures were independent of the transpiring leaf surface. A breakpoint at high rSWC indicated a more drought-sensitive plant that closed stomata early during the dehydration cycle and consequently showed stronger plasticity in leaf-level WUE i parameters. None of the sensitivity, plasticity, or water-use measurements were able to predict the overall growth performance; however, there was a general trade-off between vegetative and reproductive biomass. PCA and hierarchical clustering revealed that C24 was unique among the 35 ecotypes in uniting all the beneficial water use and stress tolerance traits, while also maintaining above average plant growth. We propose that a short dehydration cycle, measuring drought sensitivity and VWU is a fast and reliable screen for plant water use and drought response strategies.

Project description:BackgroundThe Myxococcales are well known for their predatory and developmental social processes, and for the molecular complexity of regulation of these processes. Many species within this order have unusually large genomes compared to other bacteria, and their genomes have many genes that are unique to one specific sequenced species or strain. Here, we describe RNAseq based transcriptome analysis of the FruA regulon of Myxococcus xanthus and a comparative RNAseq analysis of two Myxococcus species, M. xanthus and Myxococcus stipitatus, as they respond to starvation and begin forming fruiting bodies.ResultsWe show that both species have large numbers of genes that are developmentally regulated, with over half the genome showing statistically significant changes in expression during development in each species. We also included a non-fruiting mutant of M. xanthus that is missing the transcriptional regulator FruA to identify the direct and indirect FruA regulon and to identify transcriptional changes that are specific to fruiting and not just the starvation response. We then identified Interpro gene ontologies and COG annotations that are significantly up- or down-regulated during development in each species. Our analyses support previous data for M. xanthus showing developmental upregulation of signal transduction genes, and downregulation of genes related to cell-cycle, translation, metabolism, and in some cases, DNA replication. Gene expression in M. stipitatus follows similar trends. Although not all specific genes show similar regulation patterns in both species, many critical developmental genes in M. xanthus have conserved expression patterns in M. stipitatus, and some groups of otherwise unstudied orthologous genes share expression patterns.ConclusionsBy identifying the FruA regulon and identifying genes that are similarly and uniquely regulated in two different species, this work provides a more complete picture of transcription during Myxococcus development. We also provide an R script to allow other scientists to mine our data for genes whose expression patterns match a user-selected gene of interest.

Dataset Information

Natural variation in developmental life-history traits of the bacterium Myxococcus xanthus.

Publications

Natural variation in developmental life-history traits of the bacterium Myxococcus xanthus.

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