Uptake and subcellular partitioning of trivalent metals in a green alga: comparison between Al and Sc

Despite 40+ years of research on aluminum (Al) toxicity in aquatic organisms, Al transport mechanisms through biological membranes, and the intracellular fate of Al once assimilated, remain poorly understood. The trivalent metal scandium shares chemical similarities with Al and, unlike Al, it has a convenient radioactive tracer (Sc-46) allowing for relatively simple measurements at environmentally relevant concentrations. Thus, we investigated the potential of Sc to substitute for Al in uptake and intracellular fate studies with the green alga Chlamydomonas reinhardtii. Short-term (<60 min) competitive uptake experiments indicated that Al does not inhibit Sc influx, implying that these metals do not share a common transport mechanism. Also, internalized Al concentrations were ~4 times higher than Sc concentrations after long-term (72 h) exposures under similar conditions (4.5 μM Al_T or Sc_T, 380 μM F_T, pH 7.0, 3.8 pM Al _calc ³⁺ and 1.0 pM Sc _calc ³⁺ ). However, interesting similarities were observed in their relative subcellular distributions, suggesting possible common toxicity/tolerance mechanisms. Both metals mostly distributed to the organelles fraction and almost no association was found with the cytosolic proteins. The greatest difference was observed in the cellular debris fraction (membranes and nucleus) where Al was much more concentrated than Sc. However, it is not clear whether or not this fraction contained extracellular metal associated with the algal surface. To summarize, Sc does not seem to be an adequate substitute of Al for transport/uptake studies, but could be for investigations of toxicity/tolerance mechanisms in C. reinhardtii. Further work is needed to verify this latter suggestion.     

Barth syndrome: Cellular compensation of mitochondrial dysfunction and apoptosis inhibition due to changes in cardiolipin remodeling linked to tafazzin (TAZ) gene mutation

Cardiolipin is a mitochondrion-specific phospholipid that stabilizes the assembly of respiratory chain complexes, favoring full-yield operation. It also mediates key steps in apoptosis. In Barth syndrome, an X chromosome-linked cardiomyopathy caused by tafazzin mutations, cardiolipins display acyl chain modifications and are present at abnormally low concentrations, whereas monolysocardiolipin accumulates. Using immortalized lymphoblasts from Barth syndrome patients, we showed that the production of abnormal cardiolipin led to mitochondrial alterations. Indeed, the lack of normal cardiolipin led to changes in electron transport chain stability, resulting in cellular defects. We found a destabilization of the supercomplex (respirasome) I + III₂ + IV_n but also decreased amounts of individual complexes I and IV and supercomplexes I + III and III + IV. No changes were observed in the amounts of individual complex III and complex II. We also found decreased levels of complex V. This complex is not part of the supercomplex suggesting that cardiolipin is required not only for the association/stabilization of the complexes into supercomplexes but also for the modulation of the amount of individual respiratory chain complexes. However, these alterations were compensated by an increase in mitochondrial mass, as demonstrated by electron microscopy and measurements of citrate synthase activity. We suggest that this compensatory increase in mitochondrial content prevents a decrease in mitochondrial respiration and ATP synthesis in the cells. We also show, by extensive flow cytometry analysis, that the type II apoptosis pathway was blocked at the mitochondrial level and that the mitochondria of patients with Barth syndrome cannot bind active caspase-8. Signal transduction is thus blocked before any mitochondrial event can occur. Remarkably, basal levels of superoxide anion production were slightly higher in patients' cells than in control cells as previously evidenced via an increased protein carbonylation in the taz1Δ mutant in the yeast. This may be deleterious to cells in the long term. The consequences of mitochondrial dysfunction and alterations to apoptosis signal transduction are considered in light of the potential for the development of future treatments.     

The Calpain/Calpastatin System Has Opposing Roles in Growth and Metastatic Dissemination of Melanoma

Conventional calpains are ubiquitous cysteine proteases whose activity is promoted by calcium signaling and specifically limited by calpastatin. Calpain expression has been shown to be increased in human malignant cells, but the contribution of the calpain/calpastatin system in tumorigenesis remains unclear. It may play an important role in tumor cells themselves (cell growth, migration, and a contrario cell death) and/or in tumor niche (tissue infiltration by immune cells, neo-angiogenesis). In this study, we have used a mouse model of melanoma as a tool to gain further understanding of the role of calpains in tumor progression. To determine the respective importance of each target, we overexpressed calpastatin in tumor and/or host in isolation. Our data demonstrate that calpain inhibition in both tumor and host blunts tumor growth, while paradoxically increasing metastatic dissemination to regional lymph nodes. Specifically, calpain inhibition in melanoma cells limits tumor growth in vitro and in vivo but increases dissemination by amplifying cell resistance to apoptosis and accelerating migration process. Meanwhile, calpain inhibition restricted to host cells blunts tumor infiltration by immune cells and angiogenesis required for antitumor immunity, allowing tumor cells to escape tumor niche and disseminate. The development of highly specific calpain inhibitors with potential medical applications in cancer should take into account the opposing roles of the calpain/calpastatin system in initial tumor growth and subsequent metastatic dissemination.     

Subpopulations of Staphylococcus aureus Clonal Complex 121 Are Associated with Distinct Clinical Entities

We investigated the population structure of Staphylococcus aureus clonal complex CC121 by mutation discovery at 115 genetic housekeeping loci from each of 154 isolates, sampled on five continents between 1953 and 2009. In addition, we pyro-sequenced the genomes from ten representative isolates. The genome-wide SNPs that were ascertained revealed the evolutionary history of CC121, indicating at least six major clades (A to F) within the clonal complex and dating its most recent common ancestor to the pre-antibiotic era. The toxin gene complement of CC121 isolates was correlated with their SNP-based phylogeny. Moreover, we found a highly significant association of clinical phenotypes with phylogenetic affiliations, which is unusual for S. aureus. All isolates evidently sampled from superficial infections (including staphylococcal scalded skin syndrome, bullous impetigo, exfoliative dermatitis, conjunctivitis) clustered in clade F, which included the European epidemic fusidic-acid resistant impetigo clone (EEFIC). In comparison, isolates from deep-seated infections (abscess, furuncle, pyomyositis, necrotizing pneumonia) were disseminated in several clades, but not in clade F. Our results demonstrate that phylogenetic lineages with distinct clinical properties exist within an S. aureus clonal complex, and that SNPs serve as powerful discriminatory markers, able to identify these lineages. All CC121 genomes harboured a 41-kilobase prophage that was dissimilar to S. aureus phages sequenced previously. Community-associated MRSA and MSSA from Cambodia were extremely closely related, suggesting this MRSA arose in the region.     

Food waste valorization via anaerobic processes: a review

The increasing production of food waste worldwide and new international regulations call for the development of new technologies to treat this biowaste. Anaerobic processes are able to treat efficiently organic wastes, producing at the same time different value-added compounds. In addition, due to the lower costs and environmental impacts associated with these processes when compared to other options, they are among the most promising technologies for food waste treatment. This article reviews the state-of-the-art dealing with treatment of food waste by anaerobic processes, with emphasis on the most recent research carried out. The different processes that are assessed are anaerobic digestion for methane production, anaerobic fermentation for hydrogen and/or volatile fatty acids production and 2-stage systems. The primary issues associated with each alternative are presented, paying special attention to accumulation of ammonia and volatile fatty acids in the reactor. In addition, the latest developments to overcome the complications of each system are also described, focusing on how they improve its stability and performance. Moreover, the relevant economic and environmental research has also been reviewed, including several life cycle analyses that compare anaerobic processes with other technologies used for food waste treatment. Different case studies are also presented. Finally, recommendations for future research for the anaerobic processes studied and options for process integration are discussed. Moving towards the idea of a circular economy, a potential biorefinery for food waste valorization is also proposed.     

Species-Specific Responses of Carnivores to Human-Induced Landscape Changes in Central Argentina

The role that mammalian carnivores play in ecosystems can be deeply altered by human-driven habitat disturbance. While most carnivore species are negatively affected, the impact of habitat changes is expected to depend on their ecological flexibility. We aimed to identify key factors affecting the habitat use by four sympatric carnivore species in landscapes of central Argentina. Camera trapping surveys were carried out at 49 sites from 2011 to 2013. Each site was characterized by 12 habitat attributes, including human disturbance and fragmentation. Four landscape gradients were created from Principal Component Analysis and their influence on species-specific habitat use was studied using Generalized Linear Models. We recorded 74 events of Conepatus chinga, 546 of Pseudalopex gymnocercus, 193 of Leopardus geoffroyi and 45 of Puma concolor. We found that the gradient describing sites away from urban settlements and with low levels of disturbance had the strongest influence. L. geoffroyi was the only species responding significantly to the four gradients and showing a positive response to modified habitats, which could be favored by the low level of persecution by humans. P. concolor made stronger use of most preserved sites with low proportion of cropland, even though the species also used sites with an intermediate level of fragmentation. A more flexible use of space was found for C. chinga and P. gymnocercus. Our results demonstrate that the impact of human activities spans across this guild of carnivores and that species-specific responses appear to be mediated by ecological and behavioral attributes.     

A high-throughput method for liquid chromatography–tandem mass spectrometry determination of plasma alkylresorcinols,biomarkers of whole grain wheat and rye intake

Plasma alkylresorcinols are increasingly analyzed in cohort studies to improve estimates of whole grain intake and their relationship with disease incidence. Current methods require large volumes of solvent (>10 ml/sample) and have relatively low daily sample throughput. We tested five different supported extraction methods for extracting alkylresorcinols from plasma and improved a normal-phase liquid chromatography coupled to a tandem mass spectrometer method to reduce sample analysis time. The method was validated and compared with gas chromatography–mass spectrometry analysis. Sample preparation with HybridSPE supported extraction was most effective for alkylresorcinol extraction, with recoveries of 77–82% from 100 μl of plasma. The use of 96-well plates allowed extraction of 160 samples per day. Using a 5-cm NH₂ column and heptane reduced run times to 3 min. The new method had a limit of detection and limit of quantification equivalent to 1.1–1.8 nmol/L and 3.5–6.1 nmol/L plasma, respectively, for the different alkylresorcinol homologues. Accuracy was 93–105%, and intra- and inter-batch precision values were 4–18% across different plasma concentrations. This method makes it possible to quantify plasma alkylresorcinols in 100 μl of plasma at a rate of at least 160 samples per day without the need for large volumes of organic solvents.