Grazing impact of different heterotrophic nanoflagellates on eukaryotic (Ostreococcus tauri) and prokaryotic picoautotrophs (Prochlorococcus and Synechococcus)

Autotrophic picoplankton (<3 microm) composed of both prokaryotes and eukaryotes are the most abundant primary producers on Earth. In this study we examined the ingestion of the picoeukaryote Ostreococcus tauri by different marine heterotrophic nanoflagellates (HNF) with various morphologies, swimming and feeding behaviours. Cultures of specific bacterivorous nanoflagellates (Rhynchomonas nasuta, Jakoba libera, and a culture of Cafeteria sp./Monosiga sp.) and natural nanoflagellate populations were used as grazers. For comparison with Ostreococcus, we used similar-sized prokaryotes as prey, Prochlorococcus and Synechococcus. We observed large species-specific differences in terms of: use of picoautotrophs among nanoflagellates, time lag between prey addition and prey consumption (0-196 h), grazing rate (0-0.12 h(-1)), growth rate (0-0.3 h(-1)) and maximum abundance of HNF reached in experimental bottles (e.g. from 10(4) to 10(5) cells ml(-1), for a natural coastal population and a Cafeteria sp./Monosiga sp. culture feeding Ostreococcus respectively). Overall, this study shows that the nanoflagellate community composition is conclusive for picoautotrophic community structure and, vice versa, the picoautotrophic community structure favours or inhibits the growth of some nanoflagellate groups.     

Ruminococcin A, a new lantibiotic produced by a Ruminococcus gnavus strain isolated from human feces

When cultivated in the presence of trypsin, the Ruminococcus gnavus E1 strain, isolated from a human fecal sample, was able to produce an antibacterial substance that accumulated in the supernatant. This substance, called ruminococcin A, was purified to homogeneity by reverse-phase chromatography. It was shown to be a 2,675-Da bacteriocin harboring a lanthionine structure. The utilization of Edman degradation and tandem mass spectrometry techniques, followed by DNA sequencing of part of the structural gene, allowed the identification of 21 amino acid residues. Similarity to other bacteriocins present in sequence libraries strongly suggested that ruminococcin A belonged to class IIA of the lantibiotics. The purified ruminococcin A was active against various pathogenic clostridia and bacteria phylogenetically related to R. gnavus. This is the first report on the characterization of a bacteriocin produced by a strictly anaerobic bacterium from human fecal microbiota.     

The Oberlin procedure for restoration of elbow flexion with the da Vinci robot: four cases

Robotics allows up to 40× visual magnification and 10× magnification of the surgeon's movements, and eliminates physiologic tremors. These properties should allow the development of mini-invasive limb surgery, especially of the brachial plexus. The purpose of this work was to test the feasibility of the restoration of elbow flexion according to the technique of Oberlin using a da Vinci robot. The authors' series included four patients (average age, 31 years) presenting with elbow flexion paralysis. They were operated on 8 months after injury using a da Vinci S robot. In three patients, the open technique (technique 1) was used, and the mini-invasive approach (technique 2) was used for the last one. Strength of elbow flexion was measured. After 1-year follow-up, all of the patients had recovered elbow flexion. No sensory or motor deficit was found in the ulnar nerve territory. There was no difficulty with technique 1; technique 2, however, required a conversion to technique 1 because of difficulty visualizing the operative field. The results of the authors' series show the feasibility of the robot-assisted technique for the Oberlin procedure. The lack of sensory feedback was not an issue. The development of specific retractors and instruments should improve the mini-invasive technique. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.     

WISE-2005: adrenergic responses of women following 56-days, 6 degrees head-down bed rest with or without exercise countermeasures

We tested the hypotheses that women completing 56 days, 6 degrees head-down bed-rest (HDBR) would have changes in sensitivity of cardiovascular responses to adrenergic receptor stimulation and that frequent aerobic and resistive exercise would prevent these changes. Twenty-four women, eight controls, eight exercisers (lower body negative pressure treadmill and flywheel resistance exercise), and eight receiving nutritional supplement but no exercise were studied in baseline and during administration of the beta-agonist isoproterenol (ISO) and the alpha- and beta-agonist norepinephrine (NOR). In the control and nutrition groups, HDBR increased heart rate (HR) and reduced stroke volume (SV), and there was a significantly greater increase in HR with ISO after HDBR. In contrast, the HR and SV of the exercise group were unchanged from pre-HDBR. After HDBR, leg vascular resistance (LVR) was greater than pre-HDBR in the exercise group but reduced in control and nutrition. LVR was reduced with ISO and increased with NOR. Changes in total peripheral resistance were similar to those of LVR but of smaller magnitude, perhaps because changes in cerebrovascular resistance index were directionally opposite to those of LVR. There were no changes in sensitivity of the vascular resistance responses to adrenergic stimulation. The HR response might reflect a change in sensitivity or a necessary response to the reduction in SV after HDBR in control and nutrition groups. The reduced peripheral vascular resistance after HDBR might help to explain orthostatic intolerance in women. Exercise was an effective countermeasure to the HDBR effects.     

Predicting future coexistence in a North American ant community

Global climate change will remodel ecological communities worldwide. However, as a consequence of biotic interactions, communities may respond to climate change in idiosyncratic ways. This makes predictive models that incorporate biotic interactions necessary. We show how such models can be constructed based on empirical studies in combination with predictions or assumptions regarding the abiotic consequences of climate change. Specifically, we consider a well‐studied ant community in North America. First, we use historical data to parameterize a basic model for species coexistence. Using this model, we determine the importance of various factors, including thermal niches, food discovery rates, and food removal rates, to historical species coexistence. We then extend the model to predict how the community will restructure in response to several climate‐related changes, such as increased temperature, shifts in species phenology, and altered resource availability. Interestingly, our mechanistic model suggests that increased temperature and shifts in species phenology can have contrasting effects. Nevertheless, for almost all scenarios considered, we find that the most subordinate ant species suffers most as a result of climate change. More generally, our analysis shows that community composition can respond to climate warming in nonintuitive ways. For example, in the context of a community, it is not necessarily the most heat‐sensitive species that are most at risk. Our results demonstrate how models that account for niche partitioning and interspecific trade‐offs among species can be used to predict the likely idiosyncratic responses of local communities to climate change.     

Missed Opportunities for Early Access to Care of HIV-Infected Infants in Burkina Faso

Objective

The World Health Organization (WHO) has recommended a universal antiretroviral therapy (ART) for all HIV-infected children before the age of two since 2010, but this implies an early identification of these infants. We described the Prevention of Mother-to-Child HIV Transmission (PMTCT) cascade, the staffing and the quality of infrastructures in pediatric HIV care facilities, in Ouagadougou, Burkina Faso.

Methods

We conducted a cross-sectional survey in 2011 in all health care facilities involved in PMTCT and pediatric HIV care in Ouagadougou. We assessed them according to their coverage in pediatric HIV care and WHO standards, through a desk review of medical registers and a semi-structured questionnaire administered to health-care workers (HCW).

Results

In 2011, there was no offer of care in primary health care facilities for HIV-infected children in Ouagadougou. Six district hospitals and two university hospitals provided pediatric HIV care. Among the 67 592 pregnant women attending antenatal clinics in 2011, 85.9% were tested for HIV. The prevalence of HIV was 1.8% (95% Confidence Interval: 1.7%–1.9%). Among the 1 064 HIV-infected pregnant women attending antenatal clinics, 41.4% received a mother-to-child HIV transmission prevention intervention. Among the HIV-exposed infants, 313 (29.4%) had an early infant HIV test, and 306 (97.8%) of these infants tested received their result within a four-month period. Among the 40 children initially tested HIV-infected, 33 (82.5%) were referred to a health care facility, 3 (9.0%) were false positive, and 27 (90.0%) were initiated on ART. Although health care facilities were adequately supplied with HIV drugs, they were hindered by operational challenges such as shortage of infrastructures, laboratory reagents, and trained HCW.

Conclusions

The PMTCT cascade revealed bottle necks in PMTCT intervention and HIV early infant diagnosis. The staffing in HIV care and quality of health care infrastructures were also insufficient in 2011 in Ouagadougou.     

Consistency between marker- and genealogy-based heritability estimates in an experimental stand of Prosopis alba (Leguminosae)

Prosopis represents a valuable forest resource in arid and semiarid regions. Management of promising species requires information about genetic parameters, mainly the heritability (h(2)) of quantitative profitable traits. This parameter is traditionally estimated from progeny tests or half-sib analysis conducted in experimental stands. Such an approach estimates h(2) from the ratio of between-family/total phenotypic variance. These analyses are difficult to apply to natural populations of species with a long life cycle, overlapping generations, and a mixed mating system, without genealogical information. A promising alternative is the use of molecular marker information to infer relatedness between individuals and to estimate h(2) from the regression of phenotypic similarity on inferred relatedness. In the current study we compared h(2) of 13 quantitative traits estimated by these two methods in an experimental stand of P. alba, where genealogical information was available. We inferred pairwise relatedness by Ritland's method using six microsatellite loci. Relatedness and heritability estimates from molecular information were highly correlated to the values obtained from genealogical data. Although Ritland's method yields lower h(2) estimates and tends to overestimate genetic correlations between traits, this approach is useful to predict the expected relative gain of different quantitative traits under selection without genealogical information.     

Alpine dandelions originated in the native and introduced range differ in their responses to environmental constraints

Few studies have compared the response of native and invasive populations under stressful conditions. Furthermore, there is little consensus as to whether a plastic response is related to invasiveness in stressful environments. Exotic species have recently been reported in the high Andes of central Chile, where individuals have to cope with drought and poor soils, in addition to extreme temperatures. We explored if the exotic species Taraxacum officinale (dandelion) has plastic responses to soil moisture and nutrient availability, and whether two sets of alpine populations derived from native and introduced populations can converge to similar plastic responses to environmental constraints. Using a common garden approach, we compared plants grown from seeds collected in alpine populations of its native range (Alps, France) and in alpine populations of its introduced range (Andes, Chile) under a drought experiment, a potassium gradient, and a nitrogen gradient. Plasticity was only found as a response to drought. Moreover, different responses were found between both origins. Andean individuals are drought-resistant, while individuals from the Alps were drought-sensitive. According to the nutrient experiments, Andean dandelions behave as a nitrogen demanding-potassium avoiding species, whereas individuals from the Alps did not show any particular dependency or repulsion tendency to either of these two nutrients. Results suggest that differences in life history traits of both derived sets of populations may have an important role in determining the response of dandelions under the evaluated conditions. However, the relative importance of genetic adaptation in these responses is still unclear. Although T. officinale is a cosmopolite weed, this is the first study that compares individuals coming from its native and invaded range under stressful conditions.     

Replacement of Mg2+ by polyamines in the aminoacylation of tRNA from Phaseolus

The ability of putrescine, spermidine and spermine to replace Mg²⁺ ions in the charging reaction of tRNA was estimated for seventeen amino acids. The polyamines promoted only the transfer reaction in the case of Leu, Ile, Val, Tyr and Arg. A synergistic effect was observed when spermine was added to a suboptimal concentration of Mg²⁺ (charging at only 5% of the optimal level). This synergistic effect was not observed for Ala, Asp-NH₂, His, Lys and Ser. Kinetic studies showed a slower aminoacylation rate in those experiments when spermine and Mg⁺² (at 5% of the Mg²⁺ optimal concn) were used together than with Mg²⁺ (at the optimal concn) alone.