Reviewing the consequences of genetic purging on the success of rescue programs

Genetic rescue is increasingly considered a promising and underused conservation strategy to reduce inbreeding depression and restore genetic diversity in endangered populations, but the empirical evidence supporting its application is limited to a few generations. Here we discuss on the light of theory the role of inbreeding depression arising from partially recessive deleterious mutations and of genetic purging as main determinants of the medium to long-term success of rescue programs. This role depends on two main predictions: (1) The inbreeding load hidden in populations with a long stable demography increases with the effective population size; and (2) After a population shrinks, purging tends to remove its (partially) recessive deleterious alleles, a process that is slower but more efficient for large populations than for small ones. We also carry out computer simulations to investigate the impact of genetic purging on the medium to long term success of genetic rescue programs. For some scenarios, it is found that hybrid vigor followed by purging will lead to sustained successful rescue. However, there may be specific situations where the recipient population is so small that it cannot purge the inbreeding load introduced by migrants, which would lead to increased fitness inbreeding depression and extinction risk in the medium to long term. In such cases, the risk is expected to be higher if migrants came from a large non-purged population with high inbreeding load, particularly after the accumulation of the stochastic effects ascribed to repeated occasional migration events. Therefore, under the specific deleterious recessive mutation model considered, we conclude that additional caution should be taken in rescue programs. Unless the endangered population harbors some distinctive genetic singularity whose conservation is a main concern, restoration by continuous stable gene flow should be considered, whenever feasible, as it reduces the extinction risk compared to repeated occasional migration and can also allow recolonization events.

     

Competition for alfalfa nodulation under metal stress by the metal‐tolerant strain Ochrobactrum cytisi Azn6.2

Legume plants, in association with rhizobia, are gaining increasing interest for heavy metal rhizoremediation. This symbiotic interaction combines the advantages of rhizoremediation and soil nitrogen enrichment. In metal polluted soils, Ochrobactrum cytisi can elicit non‐fixing nodules on legumes, including Medicago sativa. Nodulation kinetics was much slower when M. sativa plants were inoculated with O. cytisi Azn6.2 compared with the natural symbiont Ensifer meliloti 1021 and nodules were ineffective in nitrogen fixation. A competition experiment was performed using alfalfa grown on heavy metals, and co‐inoculated with equal amounts of the metal‐sensitive E. meliloti 1021 and the metal‐resistant O. cytisi Azn6.2. When plants were inoculated in non‐polluted substrates, all nodules were formed by E. meliloti 1021. Nevertheless, under increasing metal concentrations, the number of nodules occupied by O. cytisi grew. At the highest metal concentration, all nodules were elicited by O. cytisi, suggesting that the resistant species can take the place of the natural symbiont. This fact has important ecological and environmental implications when proposing legume–rhizobia symbioses for rhizoremediation and highlights the need of selecting highly resistant rhizobia in order to be competitive in polluted soils.     

Molecular Insights on the Release of Avibactam from the Acyl-Enzyme Complex

Avibactam is a non-β-lactam β-lactamase inhibitor for treating complicated urinary tract and respiratory infections caused by multidrug-resistant bacterial pathogens, a serious public health threat. Despite its importance, the release mechanism of avibactam from the enzyme-inhibitor complex has been scarcely studied from first principles, considering the total protein environment. This information at the molecular level is essential for the rational design of new antibiotics and inhibitors. In this article, we addressed the release of avibactam from the complex CTX-M-15 by means of molecular dynamics simulations and quantum mechanics/molecular mechanics calculations. This study provides molecular information not available earlier, including exploration of the potential energy surfaces, characterization of the observed intermediate, and their critical points, as well. Our results show that unlike that observed in the acylation reaction, the residues Glu166 and Lys73 would be in their neutral forms. Release of avibactam follows a stepwise mechanism in which the first stage corresponds to the formation of a tetrahedral intermediate, whereas the second stage corresponds to the cleavage of the Ser70-C7 bond, mediated by Lys73, either directly or through Ser130.     

First proposal of quality indicators and standards and recommendations to improve the healthcare in the Spanish National Registry of Hip Fracture

BackgroundThe Spanish National Hip Fracture Registry (or Registro Nacional de Fractura de Cadera, RNFC) is a database of hip fracture patients admitted to Spanish hospitals. Its goals include assessment and continuous improvement of the care process.ObjectivesTo (1) establish a series of indicators, (2) evaluate their initial fulfillment, (3) propose quality standards, (4) suggest recommendations to facilitate standards compliance, and (5) monitor the indicators.MethodThe indicators fulfilled the criteria of (1) evaluating the process or outcome, (2) being clinically relevant for patients, (3) being modifiable through changes in healthcare practice, and (4) being considered important by the RNFC participants. The first quartile obtained by the group of hospitals in each of the respective variables was proposed as the standard. The Indicators Advisory Committee (IAC) elaborated a list of recommendations for each indicator, based on the available evidence.ResultsSeven indicators were chosen. These indicators (its baseline compliance vs. the standard to be reached, respectively) were: the proportion of patients receiving surgery within 48 h (44% vs. 63%), mobilized the first postoperative day (56% vs. 86%), with antiosteoporotic medication at discharge (32% vs. 61%), with calcium supplements at discharge (46% vs. 77%), with vitamin D supplements at discharge (67% vs. 92%), who developed pressure ulcers during hospitalization (7.2% vs. 2.1%) and with independent mobility at 30 days (58% vs. 70%). The IAC has established 25 recommendations for improving care.ConclusionThe indicators and standards chosen are presented, as well as the list of recommendations. This process completes the first step to improve quality of care. The results will be evaluated 6 months after implementing the recommendations.     

Fluorescent labeling of endothelial cells allows in vivo,continuous characterization of the vascular development of Xenopus laevis

Appropriate blood supply and vascular development are necessary in development and in cancer, heart disease, and diabetes. Here, we report the use of DiI-labeled acetylated low-density lipoprotein (DiI-Ac-LDL) to label endothelial cells and characterize the vasculature of live Xenopus embryos. The atlas we have created provides a detailed map of normal vascular development against which perturbations of normal patterning can be compared. By following the development of the intersomitic vessels in real-time, we show that, while rostrocaudal gradient of maturing intersomitic vessels occurs, it is not absolute. In addition, the comparative study of the ontogeny of nerve bundles from the spinal cord of transgenic Xenopus embryos expressing green fluorescent protein in the nervous system and blood vessels demonstrates a strong anatomical correlation in neurovascular development. These studies provide the basis for understanding how the vascular system forms and assumes its complicated stereotypical pattern in normal development and in disease.     

Catalase-peroxidase KatG of Burkholderia pseudomallei at 1.7A resolution

The catalase-peroxidase encoded by katG of Burkholderia pseudomallei (BpKatG) is 65% identical with KatG of Mycobacterium tuberculosis, the enzyme responsible for the activation of isoniazid as an antibiotic. The structure of a complex of BpKatG with an unidentified ligand, has been solved and refined at 1.7A resolution using X-ray synchrotron data collected from crystals flash-cooled with liquid nitrogen. The crystallographic agreement factors R and R(free) are 15.3% and 18.6%, respectively. The crystallized enzyme is a dimer with one modified heme group and one metal ion, likely sodium, per subunit. The modification on the heme group involves the covalent addition of two or three atoms, likely a perhydroxy group, to the secondary carbon atom of the vinyl group on ring I. The added group can form hydrogen bonds with two water molecules that are also in contact with the active-site residues Trp111 and His112, suggesting that the modification may have a catalytic role. The heme modification is in close proximity to an unusual covalent adduct among the side-chains of Trp111, Tyr238 and Met264. In addition, Trp111 appears to be oxidized on C(delta1) of the indole ring. The main channel, providing access of substrate hydrogen peroxide to the heme, contains a region of unassigned electron density consistent with the binding of a pyridine nucleotide-like molecule. An interior cavity, containing the sodium ion and an additional region of unassigned density, is evident adjacent to the adduct and is accessible to the outside through a second funnel-shaped channel. A large cleft in the side of the subunit is evident and may be a potential substrate-binding site with a clear pathway for electron transfer to the active-site heme group through the adduct.     

Productive infection maintains a dynamic steady state of residual viremia in human immunodeficiency virus type 1-infected persons treated with suppressive antiretroviral therapy for five years

To provide insight into the dynamics and source of residual viremia in human immunodeficiency virus (HIV) patients successfully treated with antiretroviral therapy, 14 intensely monitored patients treated with indinavir and efavirenz sustaining HIV RNA at <50 copies/ml for >5 years were studied. Abacavir was added to the regimen of eight patients at year 5. After the first 9 months of therapy, HIV RNA levels had reached a plateau ("residual viremia") that persisted for over 5 years. Levels of residual viremia differed among patients and ranged from 3.2 to 23 HIV RNA copies/ml. Baseline HIV DNA was the only significant pretreatment predictor of residual viremia in regression models including baseline HIV RNA, CD4 count, and patient age. In the four of five patients with detectable viremia who added abacavir to their regimen after 5 years, HIV RNA levels declined rapidly. The estimated half-life of infected cells was 6.7 days. Decrease in activated memory cells and a reduction in gamma interferon production to HIV Gag and p24 antigen in ELISpot assays were observed, consistent with a decrease in HIV replication. Thus, in patients treated with efavirenz plus indinavir, levels of residual viremia were established by 9 months, were predicted by baseline proviral DNA, and remained constant for 5 years. Even after years of highly suppressive therapy, HIV RNA levels declined rapidly after the addition of abacavir, suggesting that productive infection contributes to residual ongoing viremia and can be inhibited with therapy intensification.