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Les bactéries Gram - se distinguent par la présence d’une membrane externe. Il a été démon- tré que dans une situation de limitation en glucose, E.coli se sépare en deux sous-populations présentant respectivement une faible et une forte perméabilité de la membrane externe. Ce phénomène peut être interprété comme une stratégie de ‘bet-hedging’ (distribution des risques), la sous-population présentant une membrane externe plus perméable ayant une plus grande capacité d’absorption de nutriments et la sous-population présentant une faible perméabilité membranaire étant plus résistante à un potentiel stress. Premièrement, la croissance en conditions de limitation en glucose d’un ensemble de mu- tants d’E.coli présentant des ratios différent du phénotype perméable a été évalué. Tous les mutants, à l’exception de ceux comprenant la suppression de OMPA, ont montré une meilleure croissance en conditions de limitation. Ceci semble confirmer la présence d’un mécanisme de bet-hedging mais l’évaluation de celui-ci a été complexifié par les mutations utilisées. En effet, probablement due à l’impact structurel de cette importante porine, la suppression de OMPA a entraîné une diminution de la croissance en conditions non-limitante en glucose. Dans un deuxième temps, la dynamique de la sous-population perméable a été suivie à l’aide d’une cy- tomètre en flux en ligne. Dès lors, il a été observé que plusieurs dynamiques étaient impliquées ce qui suggère que plusieurs mécanismes cellulaires entrent en jeux dans l’adaptation au manque de glucose. Plus spécifiquement, ces résultats peuvent être interprétés comme une succes- sion de deux mécanismes adaptatifs, le premier intervient rapidement et mène à une fraction de cellules ayant une capacité accrue d’absorption des nutriments et le second, plus lent, im- plique une réduction significative de la taille des cellules. En conclusion, un mécanisme de bet- hedging a été observé durant la première phase d’adaptation à la limitation en glucose, ce mé- canisme a ensuite été suivi par une modification plus approfondi de la structure cellulaire. Nos résultats soulignent le fait que les mécanismes d’adaptation d’une population microbienne à la limitation en glucose sont complexes et impliquent probablement une balance bénéfice-coût conduisant à une succession de stratégies. Gram negative bacteria are characterised by the presence of an outer membrane (OM). It has been shown that upon glucose limiting conditions the bacterial population splits into two sub- populations exhibiting low and high OM permeability respectively. Such phenomenon could be interpreted as a bet-hedging strategy, with the subpopulation expressing high OM permeability exhibiting higher nutrient uptake and the subpopulation with low OM permeability being more resistant to potential stressor. In the first part of this work, a set of E.coli mutant strains displaying different ratio between OM permeabilized and non permeabilized subpopulations have been challenged for their growth fitness under nutrient limiting conditions. Mutants with higher OM permeabilized subpopula- tion, except the ones with OMPA deletion, exhibited increased fitness under limitation, suggest- ing a bet-hedging mechanism. However, deletion of OMPA resulted in a decreased fitness, prob- ably due to the structural impact of this important porin. In a second stage, dynamics of the OM permeabilized subpopulation has been tracked based on on-line flow cytometry. A highly non-monotic dynamics was observed at this level, suggesting that several cellular mechanisms are implied in the adaptation to nutrient scarcity. More specifically, these results can be inter- preted as a succession of two adaptive mechanisms, i.e. with the first one being fast and im- plying a fraction of cells with increased nutrient uptake capacity and the second one, slower, implying a significant reduction in cell size. As a conclusion, a bet-hedging mechanism has been observed during the first phase of adaptation to nutrient limiting conditions, this mech- anism being then followed by deeper modification of the cellular structure. Our results point out the fact that the mechanisms of adaptation of a microbial population to nutrient limitation are complex and involved probably a cost-benefit effect leading to a succession of strategies.
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As human populations grow and resources are depleted, agriculture will need to use land, water, and other resources more efficiently and without sacrificing long-term sustainability. Darwinian Agriculture presents an entirely new approach to these challenges, one that draws on the principles of evolution and natural selection. R. Ford Denison shows how both biotechnology and traditional plant breeding can use Darwinian insights to identify promising routes for crop genetic improvement and avoid costly dead ends. Denison explains why plant traits that have been genetically optimized by individual selection--such as photosynthesis and drought tolerance--are bad candidates for genetic improvement. Traits like plant height and leaf angle, which determine the collective performance of plant communities, offer more room for improvement. Agriculturalists can also benefit from more sophisticated comparisons among natural communities and from the study of wild species in the landscapes where they evolved. Darwinian Agriculture reveals why it is sometimes better to slow or even reverse evolutionary trends when they are inconsistent with our present goals, and how we can glean new ideas from natural selection's marvelous innovations in wild species.
Sustainable agriculture. --- Agricultural biotechnology. --- Evolution (Biology) --- Crops --- Low-input agriculture --- Low-input sustainable agriculture --- Lower input agriculture --- Resource-efficient agriculture --- Sustainable farming --- Agriculture --- Alternative agriculture --- Crop evolution --- Agro-biotechnology --- Biotechnology --- Animal evolution --- Animals --- Biological evolution --- Darwinism --- Evolutionary biology --- Evolutionary science --- Origin of species --- Biology --- Evolution --- Biological fitness --- Homoplasy --- Natural selection --- Phylogeny --- Evolution. --- Crops - Evolution --- Agricultural biotechnology --- Sustainable agriculture --- Colin Donald. --- Green Revolution. --- adaptation. --- agricultural ecosystems. --- agricultural research. --- agriculture. --- agroecologists. --- agroecology. --- animals. --- bet-hedging. --- biodiversity. --- biotechnology. --- cheating. --- chemicals. --- competition. --- complementarity. --- conflict. --- cooperation. --- cotton farmers. --- crop diversity. --- crops. --- cultivation. --- drought tolerance. --- environmental impact. --- evolution. --- evolutionary arms races. --- evolutionary biology. --- farmers. --- food production. --- food security. --- food supply. --- fungus-growing ants. --- genes. --- genetic engineering. --- genetic improvement. --- group selection. --- intercropping. --- kin selection. --- leaf-cutter ants. --- multispecies interactions. --- mutualism. --- natural ecosystems. --- natural selection. --- nitrogen fixation. --- nutrient-use efficiency. --- nutrients. --- perennial grain crops. --- pest control. --- pesticide resistance. --- pests. --- phenotypic plasticity. --- photosynthesis. --- plant breeding. --- plants. --- population. --- refuge strategy. --- reindeer. --- reproductive success. --- resource-use efficiency. --- sanctions. --- sustainability. --- tradeoffs. --- transfer RNA. --- transportation. --- trees. --- water-use efficiency. --- watergrass. --- weeds. --- wild rice. --- wild species. --- yield.
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