Project description:Adaptive laboratory evolution is highly effective for improving desired traits through natural selection. However, its applicability is inherently constrained to growth-correlated traits precluding traits of interest that incur a fitness cost, such as metabolite secretion. Here, we introduce the concept of tacking trait enabling natural selection of fitness-costly metabolic traits. The concept is inspired from the tacking maneuver used in sailing for traversing upwind. We use first-principle metabolic models to design an evolution niche wherein the tacking trait and fitness become correlated. Adaptive evolution in this niche, when followed by the reversal to the original niche, manifests in the improvement of the desired trait due to biochemical coupling between the tacking and the desired trait. We experimentally demonstrate this strategy, termed EvolveX, by evolving wine yeasts for increased aroma production. Our results pave the way for precision laboratory evolution for biotechnological and ecological applications.
Project description:Highly enriched methanotrophic communities (> 25 serial transfers) were obtained from acidic ombrotrophic peat bogs from four boreal forest sites. The enrichment strategy involved using media conditions that were associated with the highest rates of methane uptake by the original peat samples, namely, the use of diluted mineral medium of low buffering capacity, moderate incubation temperature (20 degrees C), and pH values of 3 to 6. Enriched communities contained a mixture of rod-shaped bacteria arranged in aggregates with a minor contribution of Hyphomicrobium-like cells. The growth stoichiometry of isolates was characteristic of methanotrophic bacteria (CH4/O2/CO2 = 1:1.1:0.59), with an average apparent yield of 0.41 +/- 0.03 g of biomass C/g of CH4-C. DNA from each enrichment yielded a PCR product of the expected size with primers for both mmoX and mmoY genes of soluble methane monooxygenase. Two types of sequences were obtained for PCR-amplified fragments of mmoX. One of them exhibited high identity to the mmoX protein of the Methylocystis-Methylosinus group, whereas the other showed an equal level of divergence from both the Methylosinus-Methylocystis group and Methylococcus capsulatus (Bath) and formed a distinct branch. The pH optimum for growth and for CH4 uptake was 4.5 to 5.5, which is very similar to that for the optimum CH4 uptake observed in the original peat samples. These methanotrophs are moderate acidophiles rather than acidotolerant organisms, since their growth rate and methane uptake were much lower at neutral pH. The growth of the methanotrophic community was enhanced by using media with a very low salt content (20 to 200 mg/liter), more typical of their natural environment. All four enriched communities grew on N-free medium.
Project description:Organisms modify and choose components of their local environments. This 'niche construction' can alter ecological processes, modify natural selection and contribute to inheritance through ecological legacies. Here, we propose that niche construction initiates and modifies the selection directly affecting the constructor, and on other species, in an orderly, directed and sustained manner. By dependably generating specific environmental states, niche construction co-directs adaptive evolution by imposing a consistent statistical bias on selection. We illustrate how niche construction can generate this evolutionary bias by comparing it with artificial selection. We suggest that it occupies the middle ground between artificial and natural selection. We show how the perspective leads to testable predictions related to: (i) reduced variance in measures of responses to natural selection in the wild; (ii) multiple trait coevolution, including the evolution of sequences of traits and patterns of parallel evolution; and (iii) a positive association between niche construction and biodiversity. More generally, we submit that evolutionary biology would benefit from greater attention to the diverse properties of all sources of selection.