Year: 2022

GENETIC BACKGROUND. "The founding strain is strictly asexual, and thus populations have evolved by natural selection and genetic drift acting on variation generated solely by spontaneous mutations that occurred during the experiment." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

NO CITRATE USERS. "In a long-term experiment, we propagated 12 populations of E. coli, all founded from the same ancestral strain, in a medium containing glucose, which is the limiting resource, and abundant citrate. For more than 30,000 generations, none of them evolved the capacity to use the citrate, although billions of mutations occurred in each population, such that any typical base pair mutation would have been tested many times in each one." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

FITNESS. "Previous analyses of this experiment have shown numerous examples of parallel phenotypic and genetic evolution. All twelve populations underwent rapid improvement in fitness that decelerated over time." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

EVOLUTIONARY PROFILES. "All evolved higher maximum growth rates on glucose, shorter lag phases upon transfer into fresh medium, reduced peak population densities, and larger average cell sizes relative to their ancestor. Ten populations evolved increased DNA supercoiling, and those populations examined to date show parallel changes in global gene-expression profiles." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

GENE SUBSTITUTIONS. "At least three genes have substitutions in all 12 populations, and several others have substitutions in many populations, even though most loci harbor no substitutions in any of them." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

DIVERGENT MUTANTS. "At the same time, there has also been some divergence between populations. Four have evolved defects in DNA repair, causing mutator phenotypes. There is subtle, but significant, between-population variation in mean fitness in the glucose-limited medium in which they evolved." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

CHANGE OF ENVIRONMENT. "In media containing other carbon sources, such as maltose or lactose, the variation in performance is much greater. And while the same genes often harbor substitutions, the precise location and details of the mutations almost always differ between the populations." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

NO CITRATE EVOLUTION. "Despite this potential, none of the 12 LTEE populations evolved the capacity to use the citrate that was present in their environment for over 30,000 generations. During that time, each population experienced billions of mutations, far more than the number of possible point mutations in the ≈4.6-million-bp genome. It must be difficult, therefore, to evolve the Cit+ phenotype, despite the ecological opportunity." http://www.pnas.org/content/105/23/7899.full View in LinkedIn

SUDDEN APPEARANCE OF CITRATE EVOLUTION. "Here we report that a Cit+ variant finally evolved in one population by 31,500 generations, and its descendants later rose to numerical dominance." For 30,000 generations there were no citrate metabolizes evolving in this defined population. http://www.pnas.org/content/105/23/7899.full View in LinkedIn

WHY SO SLOW? "A citrate-using (Cit+) variant finally evolved in one population by 31,500 generations, causing an increase in population size and diversity. The long-delayed and unique evolution of this function might indicate the involvement of some extremely rare mutation. Alternately, it may involve an ordinary mutation, but one whose physical occurrence or phenotypic expression is contingent on prior mutations in that population." http://www.pnas.org/content/105/23/7899.full View in LinkedIn