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At least 37 records · Page 2Linked to original sources
PubMed1978

Experimental evolution of a new enzymatic function. II. Evolution of multiple functions for ebg enzyme in E. coli.

The evolution of ebgo enzyme of Escherichia coli, an enzyme which is unable to hydrolyze lactose, lactulose, lactobionate, or galactose-arabinoside effectively, has been directed in successive steps so that the evolved enzyme is able to hydrolyze these galactosides effectively. I show that in order for a strain of E. coli with a lacZ deletion to evolve the ability to use lactobionate as a carbon source, a series of mutations must occur in the ebg genes, and that these mutations must be selected in a particular order. The ordered series of mutations constitutes an obligatory evolutionary pathway for the acquisition of a new function for ebgo enzyme. A comparison of newly evolved strains with parental strains shows that when ebg enzyme acquires a new function, its old functions often suffer; but that in several cases old functions are either unaffected or are improved. I conclude that divergence of functions catalyzed by an enzyme need not require gene duplication.

Biological Evolution↗
PubMed1995

Emergence of nylon oligomer degradation enzymes in Pseudomonas aeruginosa PAO through experimental evolution.

Through selective cultivation with 6-aminohexanoate linear dimer, a by-product of nylon-6 manufacture, as the sole source of carbon and nitrogen, Pseudomonas aeruginosa PAO, which initially has no enzyme activity to degrade this xenobiotic compound, was successfully expanded in its metabolic ability. Two new enzyme activities, 6-aminohexanoate cyclic dimer hydrolase and 6-aminohexanoate dimer hydrolase, were detected in the adapted strains.

Amidohydrolases↗
PubMed1983

Experimental evolution of a metabolic pathway for ethylene glycol utilization by Escherichia coli.

Spontaneous mutants of Escherichia coli able to grow on ethylene glycol as a sole source of carbon and energy were obtained from mutants that could grow on propylene glycol. Attempts to obtain ethylene glycol-utilizing mutants from wild-type E. coli were unsuccessful. The two major characteristics of the ethylene glycol-utilizing mutants were (i) increased activities of propanediol oxidoreductase, an enzyme present in the parental strain (a propylene glycol-positive strain), which also converted ethylene glycol into glycolaldehyde; and (ii) constitutive synthesis of high activities of glycolaldehyde dehydrogenase, which converted glycolaldehyde to glycolate. Glycolate was metabolized via the glycolate pathway, which was present in the wild-type cells; this was indicated by the induction in ethylene glycol-grown cells of glycolate oxidase, the first enzyme in the pathway. Glycolaldehyde dehydrogenase was partially characterized as an enzyme of this new metabolic pathway in E. coli, and glycolate was identified as the product of the reaction. This enzyme used NAD and NADP as coenzymes, although the NADP-dependent activity was about 10 times lower than the NAD-dependent activity. Uptake of [14C]ethylene glycol was dependent on the presence of the enzymes capable of metabolism of ethylene glycol. Glycolaldehyde and glycolate were identified as intermediate metabolites in the pathway.

Acetaldehyde↗
PubMed1985

Experimental evolution of penicillin G acylases from Escherichia coli and Proteus rettgeri.

Proteus rettgeri and Escherichia coli W were shown to express structurally different penicillin G acylases. The enzymes had similar substrate specificity but differed in molecular weight, isoelectric point, and electrophoretic mobility in polyacrylamide gels and did not antigenically cross-react. When the organisms were subjected to environmental conditions which made expression of this enzyme essential for growth, spontaneous mutants were isolated that used different amides as the only source of nitrogen. These mutants acquired the ability to use amides for growth by deregulating the penicillin G acylase and by their evolution to novel substrate specificities. The enzymes expressed by mutants isolated from each genus appeared to have evolved in parallel since each acylase attained similar new substrate specificities when the organisms were subjected to identical selection pressure.

Amidohydrolases↗
PubMedDate not supplied

[Experimental evolutive cycle of Diphyllobothrium erinaceieuropei in Paracyclops fimbriatus, tadpoles of Bufo arenarum and dogs].

Experiments were performed in order to develop the life cycle of Diphyllobothrium erinaceieuropei Rudolphi 1819 (Cestoda, Pseudophyllidea) in Paracyclops fimbriatus and Bufo arenarum as intermediate hosts and dogs as definitive hosts. The eggs of Diphyllobothrium erinaceieuropei from faeces of naturally infected dogs were kept refrigered, in water. In order to obtain coracidiums they were incubated at 25 degrees C, and then were placed in a flask which contained Paracyclops fimbriatus. The copepods were observed to be infected with procercoids 12 days after, (mean temperature 22.6 degrees C) and then, ten tadpoles of Bufo arenarum were put into the same flask. The tadpoles were examined 22, 23, 61 and 107 days later, finding plerocercoids in all them (mean temperature 24.9 degrees C). On the 23rd day, 49 plerocercoids were removed from 6 tadpoles and 28 of them were fed to a bitch. On the 107th day, 11 plerocercoids were recovered from a dead tadpole and 3 of them were fed to another bitch. In the faeces of the first bitch there were observed the eggs of Diphyllobothrium erinaceieuropei 22 days post infection (d.p.i.) and part of the strobila 30 d.p.i.. In the faeces of the second bitch the eggs were found 30 d.p.i..

Animals↗
PubMed1988

Comparative study of the action of topical heparinoids on the evolution of experimental thrombophlebitis.

The action of three different topical heparinoids on the evolution of experimental thrombophlebitis was studied. Thrombophlebitis was induced in the marginal vein of the ear of rabbits by stasis and injection of hypertonic glucose solution. Forty-eight hours later the animals were allocated to three treatment groups and a control group. The substances were applied over the affected vein three times a day for 6 days and the ears inspected daily by transilumination. After 7 days, the animals were killed and anatomopathological studies performed. No difference in thrombus frequency or inflammatory reaction was observed between the animals treated with heparinoids and the control groups, or among the treated groups.

Animals↗
PubMed2026

Predictive evolutionary genomics: principles, validation, and practice.

Climate change and habitat loss are driving rapid evolutionary responses in populations world-wide, which creates an urgent need for evolutionary forecasting in conservation and agriculture. Such forecasting can be categorized into three time scales: trait-based models that use multivariate quantitative genetic equations to project correlated phenotypic responses up to c. 20 generations, allele-based analyses that model allele frequency dynamics up to 100 generations, and composite adaptation scores that aggregate many small effects to yield predictions across longer horizons. However, these approaches have remained largely disconnected. Here, we present a Bayesian framework that integrates these three complementary approaches for evolutionary prediction. Our framework combines genomic, phenotypic, and environmental data to yield probabilistic predictions with explicit uncertainty. We show how predictive evolutionary forecasts can be validated with experimental evolution, field experimentation, historical specimens, and reciprocal transplants. These validated forecasts can help advance conservation and agricultural programmes by helping predict which populations are at risk of future extinction, optimizing breeding programmes for future climates, and planning ecosystem management under environmental change. By supporting a shift towards more predictive approaches in evolutionary biology, this framework may help improve our ability to manage biodiversity and food security in a changing world.

Genomics↗
PubMedDate not supplied

[Influence of the injection of polyethyleneglycol 400 on the evolution of experimental candidosis of the mouse (author's transl)].

The authors mention their work showing the influence of polyethyleneglycol 400 on the evolution of experimental candidosis in mice. The animals are infested by one single intra peritoneal injection of a determined number of cells of Candida albicans and then receive daily an injection of polyethyleneglycol 400 1/2 0,2 ml (Harmless dose for non infested animals). These animals die more quickly from Candida albicans septicaemia than others infested in same conditions but not treated by daily injections of polyethyleneglycol 400 1/2.

Animals↗
PubMed1976

Evolution of experimental "mutator" populations of Drosophila melanogaster.

The theory of evolution predicts that the rate of adaptation of a population is a function of the amount of genetic variation present in the population. This has been experimentally demonstrated in Drosophila populations in which genetic variability was increased either by mass hybridization of two gene pools, or by X-irradiation.--Mutator genes increase the spontaneous mutation rates of their carriers. We have now studied the effects of a third-chromosome mutator gene, mt, on the rate of adaptation of laboratory populations. Initially, experimental and control populations had similar genetic constitutions except for the presence of absence of the mt gene. The populations were maintained for 20-25 generations by "serial transfer" under conditions of very intense selection.--The number of flies produced per unit time remained constant throughout the experiment in the experimental as well as in the control populations. However, in the mutator-carring populations the average longevity of the flies (and consequently the average population size) gradually decreased. Under the experimental conditions natural selection is unable to counteract completely the increased input of deleterious mutations due to the mt gene.

Animals↗
PubMedDate not supplied

Ultrastructural studies of the dying-back process. III. The evolution of experimental peripheral giant axonal degeneration.

The spatio-temporal evolution of peripheral giant axonal degeneration has been studied in rats during the development of concurrent peripheral (PNS) and central (CNS) nervous system dying-back disease after chronic intoxication with the neurotoxic hexacarbons n-hexane (CH3CH2CH2CH2CH2CH3), methyl n-butyl ketone (MBK) (CH3COCH2CH2CH2CH3), or 2,5-hexanedione (CH3COCH2CH2CHOCH3), a neurotoxic metabolite of MBK. Each compound caused animals insidiously to develop identical, symmetrical peripheral neuropathies characterized by eversion and drop of hindfeet, inability to extend hindlimbs and upper extremity weakness. Teased fiber studies demonstrated that giant axonal swellings first developed on the proximal sides of multiple paranodes sited in distal, non-terminal regions of large myelinated fibers. Later, swellings developed at internodal sites. Smaller myelinated and unmyelinated fibers also underwent multifocal, giant axonal swelling. In affected myelinated fibers, swollen nodal and paranodal axons were frequently associated with retracted paranodal myelin sheaths. Adjacent distal internodes were attenuated and corrugated. Demyelinated paranodes apparently underwent local shrinkage and remyelination before complete distal fiber breakdown commenced. The proximal limits of chains of homogeneous myelin ovoids were interfaced with proximal, preserved regions at sites of giant axonal swellings. Regeneration of myelinated axons also occurred during intoxication. Regenerating fibers wre composed of multiple, short, branched internodes which sometimes appeared multifocally swollen. Interfaces between regenerating and preserved portions of fibers were unswollen. Thick section studies showed that pronounced endoneurial edema accompanied fiber degeneration in peripheral nerve trunks. Ultrastructural studies revealed multifocal, giant axonal swellings containing masses of 10 nm neurofilaments and sometimes, clustered mitochondria, neurotubules and smooth endoplasmic reticulum. Enlarged granular mitochondria, interdigitated Schwann cell/axon networks and corrugated myelin sheaths were common findings. Dense granules, vesicles and hexagonal particles were also noted in the axoplasm. These findings provide new insights into the nature of the dying-back process: although there was a retrograde, temporal spread of axonal swelling up affected nerve trunks, axonal degeneration neither began in the nerve terminal nor spread seriatim centripetally along individual nerve fibers. The dying-back process was further examined in a companion study in this issue (32) which analyzed some of the factors determining the differential vulnerability of PNS and CNS fibers in animals intoxicated either with these neurotoxic hexacarbons or with acrylamide.

Alkanes↗
PubMedDate not supplied

[Effects of chronic ethanol intoxication on the evolution of experimental trypanosomiasis cruzi in mice].

The effect of chronic ethyl alcohol intoxication on the evolution of Trypanosoma cruzi infection in mice was studied by two experimental procedures: (1) mice after 60 days of infection with a myotropic strain of T. cruzi were submitted to chronic alcoholic intoxidation receiving a 7% ethanol solution as only liquid source for six months; (2) mice chronically intoxicated with ethanol during five months were infected with the same strain of T. cruzi and were followed up for 45 days drinking the 7% alcoholic solution. In comparison with the infected group, not treated with ethanol, the infected mice that received the ethanol showed: a) similar mortality in the two experiments; (b) higher parasitemia in the acute phase and more frequent blood parasites in the chronic phase; (c) myocarditis with less severe cellular exudation but with increased fibrosis; (d) in the skeletal muscle, milder myositis and low frequency of arteritis and hyaline thrombi.

Alcoholism↗
PubMed2025

Adaptation of the Cyst Nematode Globodera pallida to the Colinear Potato Resistant QTLs GpaVvrn and GpaVspl Involved Distinct Genomic Regions and Absence of Cross-Virulence.

The use of alternative methods to control cyst nematode populations has accelerated since the ban of chemical nematicides in Europe. The resistant QTL GpaVvrn, derived from the wild species Solanum vernei, is widely present in resistant European potato cultivars and provides strong protection against Globodera pallida populations although a risk of resistance breakdown has already been demonstrated in both experimental evolution studies and field populations. The wild relative S. sparsipilum, harbouring the resistant QTL GpaVspl, would be an interesting alternative source of resistance to control virulent G. pallida. The goal of the present study was to understand the genomics of adaptation of the nematode to these two colinear resistant QTLs. Starting with two natural populations, an experimental evolution approach allowed, after 10 generations on resistant potato genotypes, selecting independent nematode lineages adapted to each QTL. These virulent lineages were analysed through a combination of phenotyping and genome scans approaches. Phenotyping enabled the quantification of virulence levels and confirmed resistance breakdowns. Pool-Seq whole genome sequencing followed by genome scan analyses identified genomic regions under selection, potentially involved in the adaptive mechanisms to each resistance factor. Candidate genes within these regions provided insights into the genetic basis of adaptation, revealing effectors known to suppress plant immunity. As genome scans highlighted distinct genomic regions for the adaptation to both resistant factors, we were able to predict and phenotypically confirm the absence of cross-virulence between nematode lineages evolving on GpaVvrn and GpaVspl. These findings have significant implications for the design of effective and sustainable resistance management strategies.

Animals↗
PubMed1987

Codification and evolution of experimentally observed specific recognition sites for restriction enzymes on DNA.

The list of published restriction endonucleases along with their substrates provides an excellent data base for the evaluation of the evolution and codification of the key elements for specific recognition sites on the DNA. In this paper the considerations will be limited to palindromic tetramer-, pentamer-, and hexamer-sequences. It is basically assumed that each base pair within these sequences has to be recognized by directionally unique bidentate hydrogen bonds either within the plane of the base pair or by bridging the appropriate H-bond donor/acceptor groups of the neighbouring bases of the same strand. Thus sequence specificity is mediated by twelve (eight) H-bonds, originating from the protein recognition modules. Besides a pronounced preference for GC base pairs expressed by their high frequency in the most abundant sequences, serving the need of maximal thermodynamic stability of the double helical substrates, it can also be shown that the stacking of consecutive bases within the recognition site sequences plays a major role in shaping the particular DNA/protein interface. Finally it will be demonstrated that the full set of sequences discussed in this paper can readily be derived by stepwise expanding the vocabulary of three simple tetrameric sequences by inserting single base pairs into the centre of a minimal sequence, thus creating all the published pentameric restriction sites, or by inserting/adding two GC base pairs in a palindromic way, thus creating the known multiplicity of hexameric sites.

Base Sequence↗
PubMed1989

Evolution of experimental mild and severe chronic renal failure in the rat. Mathematical models.

Two degrees of renal insufficiency were obtained in female Wistar rats, one mild (M) and the other severe (S) by surgical resection of 2/3 or 3/4 of one kidney, followed by contralateral nephrectomy. The serum creatinine concentration (Cr) s was evaluated as an index of renal function and followed in the two mentioned groups under a normal protein diet and in "S" also under a low protein diet. The evolution was assessed by two functions of time: 1/(Cr) s and log e (Cr) s. Several differences between M and S were detected. In M a smaller initial and maximal increase in (Cr) s than in S followed by a plateau was observed; in S a decrease in (Cr) s posterior to the initial increase was detected attributed to hyperfiltration followed by a sustained increment. The lowering of protein content in the diet caused a decrement in (Cr) s. In both groups a better adjustment with the logarithmic than with the inverse function was obtained, although poorer in S rats owing to a larger variability. In order to look for a mathematical link between inulin clearance (Cl In) and (Cr) s, the relationship between Cl In vs. 1/(Cr) s, and log e Cl In vs. log e (Cr) s was studied in normal and in rats in renal insufficiency. By regression analysis we found a good adjustment with both functions from 0.58 to 1.60 mg % (Cr) s.

Animals↗