Adiabatic pumping in a superconductor-normal-superconductor weak link

We present a formalism to study adiabatic pumping through a superconductor-normal-superconductor weak link. At zero temperature, the pumped charge is related to the Berry phase accumulated, in a pumping cycle, by the Andreev bound states. We analyze in detail the case when the normal region is short compared to the superconducting coherence length. The pumped charge turns out to be an even function of the superconducting phase difference. Hence, it can be distinguished from the charge transferred due to the standard Josephson effect.

Stress and survival of aging Escherichia coli rpoS colonies

In Escherichia coli, the expression of the RpoS regulon is known to be crucial for survival in liquid cultures during stationary phase. By measuring cell viability and by transcriptome analysis, here we show that rpoS cells as well as wild-type cells survive when they form colonies on solid media.

Kinematic study of a reconstructed hip in paediatric oncology

In 1997, a large portion of the femur of a four-year-old child affected by a Ewing's sarcoma was reconstructed with an innovative technique that used a massive bone allograft, in conjunction with a vascularised fibula autograft that was directly articulated within the acetabulum. The aim of the present study was to assess the kinematic behaviour of the reconstructed hip during flexion, once the acute remodelling process observed after the operation had ceased. A few additional CT slices of the hip joint region, in a flexed position, were taken at month 33 of the follow-up. The helical axes relative to the neutral-flexion motor action were estimated: their relative positions, with respect to the anatomical femoral heads, were compared, and the translation of the anatomical head centres was estimated. The angles spanned by the two femurs were almost equal, as were the translations along the respective helical axis. The main difference between the two femurs was the distance between the estimated femoral head centres and the relative helical axes. This resulted in a non-negligible translation of 2.9 mm of the fibula head inside the acetabulum during flexion, significantly higher than the 0.5 mm found for the intact contralateral femur. The results showed that, although the transplanted fibula grew and remodelled during the follow up, the action of the reconstructed hip joint still cannot be described as a ball-and-socket.

In vitro and ex vivo activation of the TLR5 signaling pathway in intestinal epithelial cells by a commensal Escherichia coli strain

The capacity of non-pathogenic enteric bacteria to induce a pro-inflammatory response is under debate in terms of its effect on the symbiosis between the mammalian host and its commensal gut microflora. Activation of NF-kappaB and induction of interleukin-8 (IL-8) and CCL-20 by the commensal Escherichia coli strain MG1655 were first studied in vitro in the human intestinal epithelial cell (IECs) lines HT29-19A and Caco-2, transfected or not with plasmids encoding dominant negative Toll-like receptor (TLR) 5 and myeloid differentiation factor-88 (MyD88) adaptor protein. The response of enterocytes in situ was then assessed using murine ileal biopsies mounted in Ussing chambers. Commensal E. coli induced NF-kappaB DNA binding, NF-kappaB transcriptional activity, CCL-20 expression, and IL-8 secretion in the human IEC lines. E. coli MG1655 flagellin was necessary and sufficient to trigger this pro-inflammatory pathway via its interaction with TLR5 and the subsequent recruitment of the adaptor protein MyD88. Following epithelial cell polarization, signaling could be induced by live E. coli and flagellin on the apical side of HT29-19A. The in vivo relevance of our findings was confirmed, because immunohistochemical staining of murine ileum demonstrated expression of TLR5 in the apical part of enterocytes in situ. Furthermore, flagellin added on the mucosal side of murine ileal biopsies mounted in Ussing chambers induced a basolateral production of KC, a functional murine homolog of human IL-8. These findings provide strong evidence that flagellin released by flagellated commensal bacteria in the intestinal lumen can induce a pro-inflammatory response in enterocytes in vivo.

Survival versus maintenance of genetic stability: a conflict of priorities during stress

Bacteria are constantly facing many different environmental assaults, which may be of such severity that numerous survivors have important alterations in their genetic material. Some genetic systems induced in response to such stresses, for example the SOS system and the sigmaS regulon, actively participate in the generation of genetic alterations. The key priority of those genetic systems during stress is to ensure survival. Therefore, the repair of lethal DNA lesions is an absolute necessity, while perfect restoration of original genetic information is not. Furthermore, the nature of DNA lesions might render error-free repair too costly, or even impossible for stressed bacterial cells. Although the majority of these genetic alterations are deleterious, the rare advantageous alterations may have long-term evolutionary consequences independently of whether the selection of molecular mechanisms involved in their generation is linked to survival strategies or not.

Tailoring Josephson coupling through superconductivity-induced nonequilibrium

The distinctive quasiparticle distribution existing under nonequilibrium in a superconductor-insulator-normal metal-insulator-superconductor mesoscopic line is proposed as a novel tool to control the supercurrent intensity in a long Josephson weak link. We present a description of this system in the framework of the diffusive-limit quasiclassical Green-function theory and take into account the effects of inelastic scattering with arbitrary strength. Supercurrent enhancement and suppression, including a marked transition to a pi junction, are striking features leading to a fully tunable structure.

[Monitoring of pregnancy complicated by maternal-fetal isoimmunization. A comparison between two clinical protocols]

AIM

Invasive techniques such as amniocentesis and cordocentesis are used for the diagnosis and treatment of fetus at risk for anemia due to maternal red-cell alloimmunization. The purpose of this study was to determine the value of non invasive measurements of the peak velocity middle cerebral artery in the fetus (PVMCA) for the diagnosis of fetal anemia.

METHODS

From 1996 to September 2002, we studied 23 pregnancies with anti D title >1:32. In the 1(st) group of 11 women (from 1996 to 1999) fetal anemia was detected by invasive techniques (amniocentesis and cordocentesis). In the 2(nd) group of 12 women (from 1999 to 2002) fetal anemia was suspected on the basis of PVMCA. When PVMCA was significantly increased, cordocentesis was performed in order to rule out fetal anemia and to provide in utero transfusions.

RESULTS

In the 1(st) period we performed 23 invasive techniques (7 amniocentesis and 16 cordocentesis) in 11 women, but we identified fetal anemia only in 4 cases. In the 2(nd) period we performed only 2 cordocentesis in women in which PVMCA was increased; the blood sampling confirmed fetal anemia in both cases.

CONCLUSION

PVMCA and fetal hematocrit are highly significantly correlated: high values of PVMCA are associated with fetal anemia. Doppler velocity of PVMCA is related to fetal anemia with positive predictive value 100% and negative predictive value 100%. The middle cerebral artery blood velocity is a non invasive technique for detecting anemia in pregnancies complicated by alloimmunization.

Management of patients with syncope referred urgently to general hospitals

OBJECTIVE

To evaluate the incidence and the strategy of management of syncope admitted urgently to a general hospital.

BACKGROUND

The management of patients with syncope is not standardized.

METHODS

The study was a prospective observational registry from a sample of 28 general hospitals in Italy and enroled all consecutive patients referred to their emergency rooms from November 5th 2001 to December 7th 2001 who were affected by transient loss of consciousness as the principal symptom.

RESULTS

The incidence of syncope was 0.95% (996 of 105,173 patients attending). Forty-six percent were hospitalized, mostly in the Department of Internal Medicine. The mean in-hospital stay was 8.1+/-5.9 days. A mean of 3.48 tests was performed per patient. A definite diagnosis was made in 80% of cases, neurally-mediated syncope being the most frequent. The findings of each of the 28 hospitals participating in the survey were separately evaluated. We observed great inter-hospital and inter-department heterogeneity regarding the incidence of emergency admission, in-hospital pathways, most of the examinations performed and the final assigned diagnosis. For example, the execution of carotid sinus massage ranged from 0% in one hospital to 58% in another (median 12.5%); tilt testing ranged from 0 to 50% (median 5.8%); the final diagnosis of neurally-mediated syncope ranged from 10 to 78.6% (median 43.3%).

CONCLUSION

Great inter-hospital and inter-department heterogeneity in the incidence and management of syncope was observed in general hospitals. As a consequence, we were unable to describe a uniform strategy for the management of syncope in everyday practice.

Stress-induced mutagenesis in bacteria

The evolutionary significance of stress-induced mutagenesis was evaluated by studying mutagenesis in aging colonies (MAC) of Escherichia coli natural isolates. A large fraction of isolates exhibited a strong MAC, and the high MAC variability reflected the diversity of selective pressures in ecological niches. MAC depends on starvation, oxygen, and RpoS and adenosine 3',5'-monophosphate regulons; thus it may be a by-product of genetic strategies for improving survival under stress. MAC could also be selected through beneficial mutations that it generates, as shown by computer modeling and the patterns of stress-inducible and constitutive mutagenesis. We suggest that irrespective of the causes of their emergence, stress-induced mutations participate in adaptive evolution.

Mechanical strength of a femoral reconstruction in paediatric oncology: a finite element study

In 1997 the proximal femur of a four-year-old child affected by a Ewing sarcoma was reconstructed using a massive bone allograft in conjunction with a vascularized fibula autograft. During the first three years of follow-up the reconstruction underwent important morphological changes. The aim of the present study was to evaluate the risk of fracture of the reconstructed proximal femur, once the physiological loads are restored, associated with a short, slow but unprotected level walk. Subject-specific finite element models of the operated femur, and of the intact contralateral one, were generated from a computed tomography exam, taken for routine clinical monitoring at month 33 of follow-up. The material properties were mapped on to the mesh and a loading condition comprising the hip joint reaction and the abductor muscle force was simulated. The risk of fracture was locally estimated, for the operated and intact femur, using the ratio between the bone tissue strength and the predicted Von Mises equivalent stress, taking into account the different behaviours of the bone tissue in tension or compression. The results showed that although the fibula grew dramatically during follow-up, the reconstructed femur had not recovered the whole mechanical strength of a normal femur. The reconstructed femoral neck seemed to be weaker than the contralateral one and hence at a higher fracture risk. However, no region reached the failure limit, so the model predicted no fracture of the femur if a short, slow but unprotected walk were allowed. The model predictions found an indirect clinical validation when the child was allowed to perform short unprotected walks and did not experience any fracture.

Polymorphism of genes encoding SOS polymerases in natural populations of Escherichia coli

High fidelity replicative DNA polymerases can be blocked during DNA replication by various base damages, which represents a potentially lethal event. Escherichia coli possesses three DNA polymerases, PolII, PolIV and PolV, that can continue replication over such lesions in template DNA, thus allowing for cell survival. Genes coding for these enzymes, polB, dinB, and umuCD respectively, belong to the stress-inducible SOS regulon. We have analyzed the patterns of nucleotide sequence variability of genes encoding for three SOS polymerases from E. coli natural isolates in order to identify the nature of selective forces that determine their evolution. The frequency of inferred inter-strain recombination events, and the frequency of synonymous and non-synonymous base substitutions within these genes do not deviate significantly from those observed for the control group composed of 2 genes coding for DNA polymerases PolI and PolIII and 10 metabolic genes. This suggests that the loci coding for SOS polymerases are subject to selective pressure for the maintenance of their function and specificity. The fact that genes coding for translesion-synthesis (TLS) polymerases, particularly dinB and umuC homologs, have been conserved during evolution and the present analysis suggest that their activity is essential for the cellular survival and fitness.

A computer assisted approach for monitoring and planning biological reconstructions in orthopaedic oncology: preliminary results and future perspectives

The evaluation of the mechanical strength of a reconstructed bone, and its evolution during the follow-up is, at present, almost impossible. This information, however, may prove extremely useful in clinical practice, both in the surgical planning and in the management of the rehabilitation therapy. In this work, a non-invasive technique, based on the use of finite element modelling, is presented that allows the simulation of the mechanical behaviour of a skeletal reconstructions starting from Computed Tomography data. This method was applied to study the evolution, during the first year of follow-up, of the strength of the reconstructed femur of a ten year-old child if a short, slow, level walk were allowed. The preliminary results indicate that the window sculpted by the surgeon to allow the anastomosis of the vascular pedicle acts as a stress concentrator and that the reduced bone mineral density, induced in the child's bone by the absence of load during the post-operative period, increases the stress level in the proximal femur.

[Impact of mutation rate on the adaptation of gut bacteria]

To study the role of mutator bacteria in the evolution of bacterial populations, we followed the impact of the mutation rate of Escherichia coli strains in the colonisation of the gut of axenic mice and the evolution of the mutation rate of bacterial populations living in the gut. We show that mutator bacteria have an advantage during the colonization. This adaptive advantage comes from their ability to generate adaptive mutations faster than wild type strains, mutations that allow their maintenance in the ecosystem. However, while mutator bacteria are becoming specialised to the environment they are living in, they accumulate mutations that may be deleterious or lethal in secondary environments. By following the evolution of the mutation rate of bacterial populations living in the gut of mice receiving antibiotics, we show that this therapy selects not only for antibiotic resistant mutants but also for mutator alleles that enhance mutation rates and are responsible for the appearance of the resistance. The costs of a high mutation rate, due to the accumulation of mutations, is seen in environments where changes are recurrent. In an ever-changing situation where every change is new, mutator bacteria might help the evolution of bacterial populations.

Plasmids spread very fast in heterogeneous bacterial communities

Conjugative plasmids can mediate gene transfer between bacterial taxa in diverse environments. The ability to donate the F-type conjugative plasmid R1 greatly varies among enteric bacteria due to the interaction of the system that represses sex-pili formations (products of finOP) of plasmids already harbored by a bacterial strain with those of the R1 plasmid. The presence of efficient donors in heterogeneous bacterial populations can accelerate plasmid transfer and can spread by several orders of magnitude. Such donors allow millions of other bacteria to acquire the plasmid in a matter of days whereas, in the absence of such strains, plasmid dissemination would take years. This "amplification effect" could have an impact on the evolution of bacterial pathogens that exist in heterogeneous bacterial communities because conjugative plasmids can carry virulence or antibiotic-resistance genes.

Growth and remodelling of the autologous bone transplant used in a pediatric femoral reconstruction

The aim of the present work was to assess how growth and remodelling changed the morphology of the transplanted fibula used to reconstruct the proximal femur of a 5 year old child affected by a Ewing's sarcoma during the first 3 years of follow-up. The morphological evolution of the transplant was quantitatively assessed on diagnostic images. Special software was developed to perform three-dimensional measurements on computed tomography (CT) datasets, while state-of-the-art image processing software was used for conventional radiography. The measurements were then correlated with the loads expected to act on the hip during the various stages of the rehabilitation protocol. A simple cantilever beam model was used for a gross estimate of the risk of fracture of the transplant. The results of the analysis showed that there is no clear correlation between the morphological changes of the autograft and the hip loading conditions experienced. Apart from a drastic increase in the periosteal radius in the frontal plane, occurring in the first 10 months after the operation, the growth of the transplanted fibula seems well within the ranges of the normal fibular growth. The cantilever beam model suggested that, although the autograft is currently subjected to subcritical stresses. morphological evolution could increase the risk of fracture in the next few years if a normal level of loading were allowed.

Over-representation of repeats in stress response genes: a strategy to increase versatility under stressful conditions?

The survival of individual organisms facing stress is enhanced by the induction of a set of changes. As the intensity, duration and nature of stress is highly variable, the optimal response to stress may be unpredictable. To face such an uncertain future, it may be advantageous for a clonal population to increase its phenotypic heterogeneity (bet-hedging), ensuring that at least a subset of cells would survive the current stress. With current techniques, assessing the extent of this variability experimentally remains a challenge. Here, we use a bioinformatic approach to compare stress response genes with the rest of the genome for the presence of various kinds of repeated sequences, elements known to increase variability during the transfer of genetic information (i.e. during replication, but also during gene expression). We investigated the potential for illegitimate and homologous recombination of 296 Escherichia coli genes related to repair, recombination and physiological adaptations to different stresses. Although long repeats capable of engaging in homologous recombination are almost absent in stress response genes, we observed a significant high number of short close repeats capable of inducing phenotypic variability by slipped-mispair during DNA, RNA or protein synthesis.

Prognostic role of umbilical artery Doppler velocimetry in growth-restricted fetuses

OBJECTIVE

To correlate umbilical artery Doppler velocimetry with perinatal outcome in a group of growth-restricted fetuses.

DESIGN

The study was a retrospective analysis of 578 singleton pregnancies with diagnosis of intrauterine growth restriction (IUGR), delivered in a single obstetric unit, at the Spedali Civili, Brescia, Italy, a university and teaching hospital with 3500 deliveries a year and neonatal intensive care unit (NICU).

METHODS

During 1991-99 we studied 578 pregnancies with a diagnosis of IUGR referred for Doppler velocimetry. From this population, four subsets were formed: normal umbilical artery pulsatility index (NUAPI; 334 fetuses); increased pulsatility index but with telediastolic flow (abnormal umbilical artery pulsatility index AUAPI; 137 fetuses); absent end-diastolic flow (AEDF; 70 fetuses); reverse telediastolic flow (RF; 37 fetuses). Fetal biometry, amniotic fluid and fetal-maternal Doppler velocimetry were evaluated in all patients, with biophysical profile and routine non-stress test, when indicated. The following outcomes were examined: mean gestational age at delivery, number of preterm deliveries (< 34 weeks), mean neonatal weight, Apgar score at 5 min < 7, prenatal and neonatal deaths (within the first 28 days of life), admission to the NICU and number of days spent after birth in hospital. Neonatal morbidity was analyzed, including respiratory distress syndrome (RDS), intraventricular hemorrhage (IVH, grade 2-3), necrotizing enterocolitis (NEC) and retinopathy of prematurity. Long-term neurological follow-up is still ongoing and will not be presented in this paper.

RESULTS

Out of 578 fetuses with IUGR, 547 were born alive. There were 26 neonatal deaths. The mean gestational age at delivery was 35.6 +/- 4 weeks and mean birth weight 1844 +/- 612 g. There were 28 intrauterine deaths and three elective terminations of pregnancy. A total of 60 cases (11%) were complicated by RDS, 13 cases (2.4%) by retinopathy of prematurity, IVH was present in nine cases (1.6%) and NEC in seven cases (1.3%). Total perinatal mortality was 9.8%; in the 26 cases of neonatal death, the mean week at delivery was 29.6 +/- 4 with a mean weight of 840 +/- 425 g. Patients with NUAPI had a mean week at delivery of 37 +/- 3, those with AUAPI delivered at 34 +/- 3.2, those with AEDF delivered at 31 +/- 3 and those with RF delivered at 29 +/- 2 weeks. In progressively worsening umbilical velocimetry, we observed an increase of incidence of low Apgar score. Days of admission to the NICU and incidence of perinatal mortality increased with the worsening of Doppler velocimetry.

CONCLUSIONS

Our study underlines the existence of a strict correlation between umbilical Doppler velocimetry and an increased incidence of perinatal complications in IUGR fetuses.

Mutator bacteria as a risk factor in treatment of infectious diseases

We show in a gnotobiotic mouse model that, in addition to direct selection of antibiotic-resistant bacteria, some antibiotic treatments also select for mutator alleles. Because of these mutator alleles' high mutation rates, the initial treatment failure increases the probability of failures in subsequent treatments with other drugs.

High frequency of mutator strains among human uropathogenic Escherichia coli isolates

By using a panel of 603 commensal and pathogenic Escherichia coli and Shigella isolates, we showed that mutation rates of strains vary considerably among different ecotypes. Uropathogenic strains had the highest frequency of mutators, while strains from patients with bacteremia had the lowest mutation rates. No correlation between the mutation rates and antibiotic resistance was observed among the studied strains.

The rise and fall of mutator bacteria

Bacteria with elevated mutation rates are frequently found among natural isolates. This is probably because of their ability to generate genetic variability, the substrate for natural selection. However, such high mutation rates can lead to the loss of vital functions. The evolution of bacterial populations may happen through alternating periods of high and low mutation rates. The cost and benefits of high mutation rates in the course of bacterial adaptive evolution are reviewed.

Translational misreading: a tRNA modification counteracts a +2 ribosomal frameshift

Errors during gene expression from DNA to proteins via transcription and translation may be deleterious for the functional maintenance of cells. In this paper, extensive genetic studies of the misreading of a GA repeat introduced into the lacZ gene of Escherichia coli indicate that in this bacteria, errors occur predominantly by a +2 translational frameshift, which is controlled by a tRNA modification involving the MnmE and GidA proteins. This ribosomal frameshift results from the coincidence of three events: (1) decreased codon-anticodon affinity at the P-site, which is caused by tRNA hypomodification in mnmE(-) and gidA(-) strains; (2) a repetitive mRNA sequence predisposing to slippage; and (3) increased translational pausing attributable to the presence of a rare codon at the A-site. Based on genetic analysis, we propose that GidA and MnmE act in the same pathway of tRNA modification, the absence of which is responsible for the +2 translational frameshift. The difference in the impact of the mutant gene on cell growth, however, indicates that GidA has at least one other function.

Genes and olympic performance: a co-twin study

An Olympic gold medalist in a 20 km competitive walking race and his identical twin brother, also an Olympic athlete in the same event but with inferior performance, were tested in order to obtain some further insight into the relative importance of genetic factors in modulating athletic excellence. Both twins had undergone the same strenuous, long-term training for 19 years since the age of 15 under the guidance of the same coach. An assessment of their bio-behavioural profiles at 40 years of age, i. e. 7 years after they ceased training, revealed that intrapair differences were negligible in physiological attributes but divergent in personality traits measured. Respective values for the Olympic winner and his identical counterpart were as follows: Body mass index 23.2 and 22.7, cardiac mass index 85.4 and 84.4 g x m2, squatjumping 25.3 and 27.3 cm, VO2 at running speed 9 km x h(-1) 33.1 and 33.6 ml x kg(-1) x min(-1), VO2 max 57.1 and 58.6 ml x kg(-1) x min(-1) (72.5ml x kg(-1) x min(-1) for the Olympic winner at age 22 yrs), reaction to anger 97 and 9 and anger expression 2 and 76 in percentile of the State-Trait Anger Expression Inventory. Findings suggest that although genetic constitution and years of physical training are prerequisites for making an Olympic athlete, success may be largely influenced by personality traits.

Genotoxic hazard of pollutants in cetaceans: DNA damage and repair evaluated in the bottlenose dolphin (Tursiops truncatus) by the Comet Assay

Single cell gel electrophoresis (or Comet Assay) was used for evaluation of the in vitro genotoxicity of hydrogen peroxide (used as a positive control), polychlorinated biphenyls (PCBs) (Aroclor 1254) and methyl mercury chloride, in isolated bottlenose dolphin leukocytes. Results showed that hydrogen peroxide and methyl mercury induced DNA strand breakage in a dose-dependent manner, while PCBs did not induce a clear dose-effect response at the low doses investigated. Efficiency in repairing DNA breakage induced by methyl mercury was also evaluated. Findings demonstrated that dolphin cells are characterized by higher efficiency in DNA repair when compared to human leukocytes. The observed resistance to methyl mercury toxicity in dolphins was hypothesized to be a defence strategy developed to combat high dietary exposure and compensate for limited capacity to excrete persistent pollutants.

Costs and benefits of high mutation rates: adaptive evolution of bacteria in the mouse gut

We have shown that bacterial mutation rates change during the experimental colonization of the mouse gut. A high mutation rate was initially beneficial because it allowed faster adaptation, but this benefit disappeared once adaptation was achieved. Mutator bacteria accumulated mutations that, although neutral in the mouse gut, are often deleterious in secondary environments. Consistently, the competitiveness of mutator bacteria is reduced during transmission to and re-colonization of similar hosts. The short-term advantages and long-term disadvantages of mutator bacteria could account for their frequency in nature.

The control of blood glucose in the critical diabetic patient: a neuro-fuzzy method

Conventional algorithms for regulating insulin infusion rates in those critical diabetic patients submitted to parenteral glucose and insulin infusions do not allow to approach near normal blood glucose (BG) levels since traditional control systems are not fully effective in complex nonlinear systems as BG control is. Thus, we applied fuzzy logic principles and neural network techniques to modify intravenous insulin administration rates during glucose infusion. Forty critically ill, fasted diabetic subjects submitted to glucose and potassium infusion entered the study. They were randomly assigned to two treatment regimes: in group A, insulin infusion rates were adjusted, every 4 h at any step between -1.5 and +1.5 U/h, according to a neuro-fuzzy nomogram; in control group B, insulin infusion rates were modified according to a conventional algorithm. In group A, BG was lowered below 10 mmol/l faster than in group B (8.2+/-0.7 vs. 13+/-1.8 h, P<.02). Mean BG was 7.8+/-0.2 in group A and 10.6+/-0.3 mmol/l in group B (P<.00001). BG values below 4.4 mmol/l were: A=5.8% and B=10.2%. BG values lower than 2.5 mmol/l had never been observed. In conclusion, the neuro-fuzzy control system is effective in improving the BG control in critical diabetic patients without increasing either the number of BG determinations or the risk of hypoglycemia.

Second-order selection in bacterial evolution: selection acting on mutation and recombination rates in the course of adaptation

The increase in genetic variability of a population can be selected during adaptation, as demonstrated by the selection of mutator alleles. The dynamics of this phenomenon, named second-order selection, can result in an improved adaptability of bacteria through regulation of all facets of mutation and recombination processes.

Mutator natural Escherichia coli isolates have an unusual virulence phenotype

A small percentage of natural Escherichia coli isolates (both commensal and pathogenic) have a mutator phenotype related to defects in methyl-directed mismatch repair (MR) genes. We investigated whether there was a direct link between the mutator phenotype and virulence by (i) studying the relationships between mutation rate and virulence in a mouse model of extraintestinal virulence for 88 commensal and extraintestinal pathogenic E. coli isolates and (ii) comparing the virulence in mice of MR-deficient and MR-proficient strains that were otherwise isogenic. The results provide no support for the hypothesis that the mutator phenotype has a direct role in virulence or is associated with increased virulence. Most of the natural mutator strains studied displayed an unusual virulence phenotype with (i) a lack of correspondence between the number of virulence determinants and pathogenicity in mice and (ii) an intermediate level of virulence. On a large evolutionary scale, the mutator phenotype may help parasites to achieve an intermediate rate of virulence which mathematical models predict to be selected for during long-term parasite-host interactions.

Evolutionary implications of the frequent horizontal transfer of mismatch repair genes

Mutation and subsequent recombination events create genetic diversity, which is subjected to natural selection. Bacterial mismatch repair (MMR) deficient mutants, exhibiting high mutation and homologous recombination rates, are frequently found in natural populations. Therefore, we have explored the possibility that MMR deficiency emerging in nature has left some "imprint" in the sequence of bacterial genomes. Comparative molecular phylogeny of MMR genes from natural Escherichia coli isolates shows that, compared to housekeeping genes, individual functional MMR genes exhibit high sequence mosaicism derived from diverse phylogenetic lineages. This apparent horizontal gene transfer correlates with hyperrecombination phenotype of MMR-deficient mutators. The sequence mosaicism of MMR genes may be a hallmark of a mechanism of adaptive evolution that involves modulation of mutation and recombination rates by recurrent losses and reacquisitions of MMR gene functions.

Negative length orbits in normal-superconductor billiard systems

The path-length spectra of mesoscopic systems including diffractive scatterers and connected to a superconductor are studied theoretically. We show that the spectra differ fundamentally from that of normal systems due to the presence of Andreev reflection. It is shown that negative path lengths should arise in the spectra as opposed to the normal system. To highlight this effect we carried out both quantum mechanical and semiclassical calculations for the simplest possible diffractive scatterer. The most pronounced peaks in the path-length spectra of the reflection amplitude are identified by the routes that the electron and/or hole travels.

No genetic barriers between Salmonella enterica serovar typhimurium and Escherichia coli in SOS-induced mismatch repair-deficient cells

Conjugational crosses trigger SOS induction in Escherichia coli F(-) cells mated with Salmonella enterica serovar Typhimurium Hfr donors. Using an epigenetic indicator of SOS induction, we showed that a strong SOS response occurring in a subpopulation of mated mismatch repair-deficient cells totally abolishes genetic barriers between these two genera.

Mutators and sex in bacteria: conflict between adaptive strategies

Bacterial mutation rates can increase and produce genetic novelty, as shown by in vitro and in silico experiments. Despite the cost due to a heavy deleterious mutation load, mutator alleles, which increase the mutation rate, can spread in asexual populations during adaptation because they remain associated with the rare favorable mutations they generate. This indirect selection for a genetic system generating diversity (second-order selection) is expected to be highly sensitive to changes in the dynamics of adaptation. Here we show by a simulation approach that even rare genetic exchanges, such as bacterial conjugation or transformation, can dramatically reduce the selection of mutators. Moreover, drift or competition between the processes of mutation and recombination in the course of adaptation reveal how second-order selection is unable to optimize the rate of generation of novelty.

Protein oxidation in response to increased transcriptional or translational errors

In this study, we show a correlation between synthesis of aberrant proteins and their oxidative modification. The level of aberrant proteins was elevated in Escherichia coli cultures by decreasing transcriptional or translational fidelity using specific mutations or drugs. Protein carbonylation, an oxidative modification, increased in parallel to the induction of the heat shock chaperone GroEL. As the protein turnover rates and level of intracellular oxidative stress remained unchanged, it appears that carbonylation results from the increased susceptibility of the misfolded proteins. These studies show that the cellular protein oxidation is not limited only by available reactive oxygen species, but by the levels of aberrant proteins. Thus, protein oxidation seen in aging cells may be the consequence also of reduced transcriptional/translational fidelity, and protein structures appear to have evolved to minimize oxidative damage. In addition, we discuss the possibility that carbonylation, being an unrepairable protein modification, may serve as a tagging system to shunt misfolded proteins between pathways of refolding by chaperones or the proteolytic apparatus.

Evolution-driving genes

Genomic sequences provide evidence for a common origin of life and its evolution via selection of genetic variants created by mutation and recombination. Two classes of genes are known to accelerate mutation and/or recombination rates in bacterial populations: stress-inducible wild-type genes, usually part of the SOS regulon, and genes whose functional loss, or downregulation, increases the rate of genetic variability (mutator and/or hyper-rec mutants).

Mutators, population size, adaptive landscape and the adaptation of asexual populations of bacteria

Selection of mutator alleles, increasing the mutation rate up to 10, 000-fold, has been observed during in vitro experimental evolution. This spread is ascribed to the hitchhiking of mutator alleles with favorable mutations, as demonstrated by a theoretical model using selective parameters corresponding to such experiments. Observations of unexpectedly high frequencies of mutators in natural isolates suggest that the same phenomenon could occur in the wild. But it remains questionable whether realistic in natura parameter values could also result in selection of mutators. In particular, the main parameters of adaptation, the size of the adapting population and the height and steepness of the adaptive peak characterizing adaptation, are very variable in nature. By simulation approach, we studied the effect of these parameters on the selection of mutators in asexual populations, assuming additive fitness. We show that the larger the population size, the more likely the fixation of mutator alleles. At a large population size, at least four adaptive mutations are needed for mutator fixation; moreover, under stronger selection stronger mutators are selected. We propose a model based on multiple mutations to illustrate how second-order selection can optimize population fitness when few favorable mutations are required for adaptation.

Evolution of evolvability

Genomic sequence data provide evidence for a common origin of life and for its evolution by genetic variation via mutation and recombination. This paper discusses the fundamental dialectic paradigm of evolution--stability versus variability--at the crossroads of molecular genetics, population genetics, ecology, and the emerging science of experimental evolution. Experimental evolution of molecules, viruses, and bacteria can be used not only to test some basic evolutionary hypotheses but also to create new organisms for applications in biotechnology, agriculture, and medicine.

Doppler echocardiography of the main stems of the pulmonary arteries in the normal human fetus

The objective of this study was to describe the normal blood flow velocity waveforms in the main branches of the right and left pulmonary arteries in the human fetus and to establish reference ranges for different Doppler parameters during the second half of pregnancy. Cross-sectional data were collected from 86 healthy human singleton fetuses between 18 and 38 weeks of gestation. With advancing gestation a significant increase (p < 0.001) in the peak systolic velocity, time averaged velocity and time velocity integral was observed. The pulsatility index decreased significantly (p < 0.05) in the same period, suggesting a decrease in the pulmonary arterial vascular resistance. The acceleration time (AT) and the ratio of AT to ejection time (AT/ET), described in postnatal cardiology as having an inverse correlation with mean arterial pressure, increased significantly (p < 0.001). This is possibly the result of decreased pulmonary arterial pressure. The data show that Doppler examination of blood flow in the main stem of both the right and the left pulmonary arteries of the fetus is feasible, and increases insight into the lung perfusion of the human fetus. The observed changes throughout gestation are in accordance with animal experiments showing an increase in perfusion as well as a decrease in the vascular resistance and pressure.

[Developmental changes of cardiac mechanics during fetal and postnatal life. Diagnostic role of Doppler echocardiography]

The advent of fetal echocardiography combined with Doppler technology gave the clinicians the possibility to evaluate and clarify the main aspects of fetal and postnatal circulatory physiology. From the end of cardiogenesis to the end of gestation the developmental changes of the fetal myocardial structure, ventricular function and circulatory physiology have all been studied. Also the physiological features of the transitional circulation in the first postnatal period, as well as the developmental changes in the morphology and function of the neonatal ventricles can be assessed by Doppler echocardiography. This review is divided in two parts. In the first one we will briefly discuss the contractile properties of the fetal myocardium, the cardiac performance and dynamics of the fetal circulation; in the second one we will consider the physiological aspects of the transitional circulation, the structural features of the immature neonatal myocardium, as well as the developmental changes of the myocardial mechanics as shown by Doppler ultrasound.

Genetic variability and adaptation to stress

Besides an immediate cellular adaptation to stress, organisms can resist such challenges through changes in their genetic material. These changes can be due to mutation or acquisition of pre-evolved functions via horizontal transfer. In this chapter we will review evidence from bacterial genetics that suggests that the frequency of such events can increase in response to stress by activating mutagenic response (e.g. the SOS response) and by inhibiting antimutagenic activities (e.g. mismatch repair system, MRS). Natural selection, by favoring adaptations, can also select for the mechanism(s) that has/have generated the adaptive changes by hitchhiking. These mutator mechanisms can sometimes respond very specifically, though blindly, to the challenge of the environment. Such stress-induced increases in mutation rates enhance genetic polymorphism, which is the structural component of the barrier to genetic exchange. Since SOS and MRS are the enzymatic controls of this barrier, the modulation of these systems can lead to a burst of speciation.

Counteraction by MutT protein of transcriptional errors caused by oxidative damage

Oxidized guanine (8-oxo-7,8-dihydroguanine; 8-oxo-G) is a potent mutagen because of its ambiguous pairing with cytosine and adenine. The Escherichia coli MutT protein specifically hydrolyzes both 8-oxo-deoxyguanosine triphosphate (8-oxo-dGTP) and 8-oxo-guanosine triphosphate (8-oxo-rGTP), which are otherwise incorporated in DNA and RNA opposite template A. In vivo, this cleaning of the nucleotide pools decreases both DNA replication and transcription errors. The effect of mutT mutation on transcription fidelity was shown to depend on oxidative metabolism. Such control of transcriptional fidelity by the ubiquitous MutT function has implications for evolution of RNA-based life, phenotypic expression, adaptive mutagenesis, and functional maintenance of nondividing cells.