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Overflow metabolism is ubiquitous in nature, and it is often considered inefficient because it leads to a relatively low biomass yield per consumed carbon. This metabolic strategy has been described as advantageous because it supports high growth rates during nutrient competition. Here, we experimentally evolved bacteria without nutrient competition by repeatedly growing and mixing millions of parallel batch cultures of Escherichia coli. Each culture originated from a water-in-oil emulsion droplet seeded with a single cell. Unexpectedly we found that overflow metabolism (acetate production) did not change. Instead, the numerical cell yield during the consumption of the accumulated acetate increased as a consequence of a reduction in cell size. Our experiments and a mathematical model show that fast growth and overflow metabolism, followed by the consumption of the overflow metabolite, can lead to a higher numerical cell yield and therefore a higher fitness compared with full respiration of the substrate. This provides an evolutionary scenario where overflow metabolism can be favorable even in the absence of nutrient competition. [ABSTRACT FROM AUTHOR]

The genome size of 51 populations of 20 species of the North American endemic sagebrushes (subgenus Tridentatae), related species, and some hybrid taxa were assessed by flow cytometry, and were analysed in a phylogenetic framework. Results were similar for most Tridentatae species, with the exception of three taxonomically conflictive species: Artemisia bigelovii Gray, Artemisia pygmaea Gray, and Artemisia rigida Gray. Genome size homogeneity (together with the high morphological, chemical, and karyological affinities, as well as low DNA sequence divergence) could support a recent diversification process in this geographically restricted group, thought to be built upon a reticulate evolutionary framework. The Tridentatae and the other North American endemic Artemisia show a significantly higher genome size compared with the other subgenera. Our comparative analyses including genome size results, together with different kinds of ecological and morphological traits, suggest an evolutionary change in lifestyle strategy linked to genome expansion, in which junk or selfish DNA accumulation might be involved. Conversely, weed or invasive behaviour in Artemisia is coupled with lower genome sizes. Data for both homoploid and polyploid hybrids were also assessed. Genome sizes are close to the expected mean of parental species for homoploid hybrids, but are lower than expected in the allopolyploids, a phenomenon previously documented to be related with polyploidy. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 631–649. [ABSTRACT FROM AUTHOR]

A mechanistic understanding of microbial community establishment and product formation in open fermentative systems can aid the development of bioprocesses utilising organic waste. Kinetically, a single rate-limiting substrate is expected to result in one dominant species. Four enrichment cultures were operated to ferment either xylose or glucose in a sequencing batch reactor (SBR) or a continuous-flow stirred tank reactor (CSTR) mode. The combination of 16S rRNA gene-based analysis and fluorescence in situ hybridisation revealed no complete dominance of one species in the community. The glucose-fed and xylose-fed SBR enrichments were dominated >80% by one species. Enterobacteriaceae dominated the SBRs enrichments, with Citrobacter freundii dominant for xylose and Enterobacter cloacae for glucose. Clostridium, Enterobacteriaceae and Lachnospiraceae affiliates dominated the CSTRs enrichments. Independent of substrate, SBR communities displayed 2–3 times higher biomass-specific rate of substrate uptake (qsmax) and 50% lower biomass yield on ATP, to CSTR communities. Butyrate production was linked to dominance of Clostridium and low qsmax (1.06 Cmols Cmolx−1 h−1), while acetate and ethanol production was linked to dominance of Enterobacteriaceae and Lachnospiraceae and high qsmax (1.72 Cmols Cmolx−1 h−1 and higher). Overall, more diversity than expected through competition was observed, indicating mutualistic mechanisms might shape microbial diversity. [ABSTRACT FROM AUTHOR]