Favorable Mutations? Help me!!

What is a "normal environment"? Has there even been a stable environment in the last 20Ky?Are the bacteria in this study in a normal or abnormal environment?Proc Natl Acad Sci U S A. 2001 Sep 25;98(20):11388-93. Related Articles, LinksContribution of individual random mutations to genotype-by-environment interactions in Escherichia coli.Remold SK, Lenski RE.Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824, USA. remold@msu.eduNumerous studies have shown genotype-by-environment (GxE) interactions for traits related to organismal fitness. However, the genetic architecture of the interaction is usually unknown because these studies used genotypes that differ from one another by many unknown mutations. These mutations were also present as standing variation in populations and hence had been subject to prior selection. Based on such studies, it is therefore impossible to say what fraction of new, random mutations contributes to GxE interactions. In this study, we measured the fitness in four environments of 26 genotypes of Escherichia coli, each containing a single random insertion mutation. Fitness was measured relative to their common progenitor, which had evolved on glucose at 37 degrees C for the preceding 10,000 generations. The four assay environments differed in limiting resource and temperature (glucose, 28 degrees C; maltose, 28 degrees C; glucose, 37 degrees C; and maltose, 37 degrees C). A highly significant interaction between mutation and resource was found. In contrast, there was no interaction involving temperature. The resource interaction reflected much higher among mutation variation for fitness in maltose than in glucose. At least 11 mutations (42%) contributed to this GxE interaction through their differential fitness effects across resources. Beneficial mutations are generally thought to be rare but, surprisingly, at least three mutations (12%) significantly improved fitness in maltose, a resource novel to the progenitor. More generally, our findings demonstrate that GxE interactions can be quite common, even for genotypes that differ by only one mutation and in environments differing by only a single factor.

Actually, I will post an example here of beneficial mutations that do not incur a cost or cause a disease yet are fixed or go to high frequency in a bacterial population over timeMicrobiology. 2001 Apr;147(Pt 4):995-1006. Related Articles, LinksRapid phenotypic change and diversification of a soil bacterium during 1000 generations of experimental evolution.Riley MS, Cooper VS, Lenski RE, Forney LJ, Marsh TL.Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824, USA.Evolutionary pathways open to even relatively simple organisms, such as bacteria, may lead to complex and unpredictable phenotypic changes, both adaptive and non-adaptive. The evolutionary pathways taken by 18 populations of Ralstonia strain TFD41 while they evolved in defined environments for 1000 generations were examined. Twelve populations evolved in liquid media, while six others evolved on agar surfaces. Phenotypic analyses of these derived populations identified some changes that were consistent across all populations and others that differed among them. The evolved populations all exhibited morphological changes in their cell envelopes, including reductions of the capsule in each population and reduced prostheca-like surface structures in most populations. Mean cell length increased in most populations (in one case by more than fourfold), although a few populations evolved shorter cells. Carbon utilization profiles were variable among the evolved populations, but two distinct patterns were correlated with genetic markers introduced at the outset of the experiment. Fatty acid methyl ester composition was less variable across populations, but distinct patterns were correlated with the two physical environments. All 18 populations evolved greatly increased sensitivity to bile salts, and all but one had increased adhesion to sand; both patterns consistent with changes in the outer envelope. This phenotypic diversity contrasts with the fairly uniform increases in competitive fitness observed in all populations. This diversity may represent a set of equally probable adaptive solutions to the selective environment; it may also arise from the chance fixation of non-adaptive mutations that hitchhiked with a more limited set of beneficial mutations.and another oneProc Natl Acad Sci U S A. 1999 Mar 30;96(7):3807-12. Related Articles, LinksGenomic evolution during a 10,000-generation experiment with bacteria.Papadopoulos D, Schneider D, Meier-Eiss J, Arber W, Lenski RE, Blot M.Abteilung Mikrobiologie, Biozentrum, CH-4056 Basel, Switzerland.Molecular methods are used widely to measure genetic diversity within populations and determine relationships among species. However, it is difficult to observe genomic evolution in action because these dynamics are too slow in most organisms. To overcome this limitation, we sampled genomes from populations of Escherichia coli evolving in the laboratory for 10,000 generations. We analyzed the genomes for restriction fragment length polymorphisms (RFLP) using seven insertion sequences (IS) as probes; most polymorphisms detected by this approach reflect rearrangements (including transpositions) rather than point mutations. The evolving genomes became increasingly different from their ancestor over time. Moreover, tremendous diversity accumulated within each population, such that almost every individual had a different genetic fingerprint after 10,000 generations. As has been often suggested, but not previously shown by experiment, the rates of phenotypic and genomic change were discordant, both across replicate populations and over time within a population. Certain pivotal mutations were shared by all descendants in a population, and these are candidates for beneficial mutations, which are rare and difficult to find. More generally, these data show that the genome is highly dynamic even over a time scale that is, from an evolutionary perspective, very brief.