High Functional Diversity in Mycobacterium tuberculosis Driven by Genetic Drift and Human Demography

Mycobacterium tuberculosis infects one third of the human world population and kills someone every 15 seconds. For more than a century, scientists and clinicians have been distinguishing between the human- and animal-adapted members of the M. tuberculosis complex (MTBC). However, all human-adapted strains of MTBC have traditionally been considered to be essentially identical. We surveyed sequence diversity within a global collection of strains belonging to MTBC using seven megabase pairs of DNA sequence data. We show that the members of MTBC affecting humans are more genetically diverse than generally assumed, and that this diversity can be linked to human demographic and migratory events. We further demonstrate that these organisms are under extremely reduced purifying selection and that, as a result of increased genetic drift, much of this genetic diversity is likely to have functional consequences. Our findings suggest that the current increases in human population, urbanization, and global travel, combined with the population genetic characteristics of M. tuberculosis described here, could contribute to the emergence and spread of drug-resistant tuberculosis.     

CFTR mediates cadmium-induced apoptosis through modulation of ROS level in mouse proximal tubule cells

The aim of this study was to characterize the role of CFTR during Cd²⁺-induced apoptosis. For this purpose primary cultures and cell lines originated from proximal tubules (PCT) of wild-type cftr^+/+ and cftr^?/? mice were used. In cftr^+/+ cells, the application of Cd²⁺ (5 μM) stimulated within 8 min an ERK1/2-activated CFTR-like Cl^? conductance sensitive to CFTR_inh-172. Thereafter Cd²⁺ induced an apoptotic volume decrease (AVD) within 6 h followed by caspase-3 activation and apoptosis. The early increase in CFTR conductance was followed by the activation of volume-sensitive outwardly rectifying (VSOR) Cl^? and TASK2 K⁺ conductances. By contrast, cftr^?/? cells exposed to Cd²⁺ were unable to develop VSOR currents, caspase-3 activity, and AVD process and underwent necrosis. Moreover in cftr^+/+ cells, Cd²⁺ enhanced reactive oxygen species (ROS) production and induced a 50% decrease in total glutathione content (major ROS scavenger in PCT). ROS generation and glutathione decrease depended on the presence of CFTR, since they did not occur in the presence of CFTR_inh-172 or in cftr^?/? cells. Additionally, Cd²⁺ exposure accelerates effluxes of fluorescent glutathione S-conjugate in cftr^+/+ cells. Our data suggest that CFTR could modulate ROS levels to ensure apoptosis during Cd²⁺ exposure by modulating the intracellular content of glutathione.     

Modelling of a metal-containing hepcidin

Hepcidin was originally identified as a liver-expressed antimicrobial peptide but further studies have shown that it also has a key role in iron homeostasis. The NMR structure of the synthetic peptides reveal a distorted beta-sheet containing 4 disulphide bridges, with an unusual vicinal disulphide bridge which has been suggested to be functionally significant. In this study, we report the presence of co-purified iron with the urine-purified 20 and 25 residue hepcidins. Since the published structure does not allow metal binding, the interaction of hepcidin with metals was investigated for other possible structural conformations by threading its primary sequence onto existing 3D folds. Several alignments were obtained and the best scores were used to build a 3D model of hepcidin containing one atom of iron. The new 3D structure, that contains only reduced Cys residues, is completely different from the solved structure of the synthetic peptide. Although the model presented here shows only one metal bound to the peptide, the binding of several metal atoms cannot be excluded from such a short flexible peptide. The co-purification of iron with both peptides, together with our 3D model, suggest a conformational polymorphism for hepcidin, reminiscent of the iron regulatory proteins IRPs.     

Synthesis and antimalarial activities of novel 3,3,6,6-tetraalkyl-1,2,4,5-tetraoxanes

The oxidative system H2O2/fluorinated alcohol (TFE, HFIP) was used for direct acid- and MeReO3-catalyzed synthesis of 1,2,4,5-tetraoxanes from cyclic (C6, C7, and C12) and acyclic ketones. The influence of ring size and alkyl chain length were studied and antimalarial activities of synthetic 3,3,6,6-tetraalkyl-1,2,4,5-tetraoxanes were determined. Variations in their antimalarial activities were significant, although they share similar electrochemical properties of the peroxide bond.     

The Putative Thiosulfate Sulfurtransferases PspE and GlpE Contribute to Virulence of Salmonella Typhimurium in the Mouse Model of Systemic Disease

The phage-shock protein PspE and GlpE of the glycerol 3-phosphate regulon of Salmonella enterica serovar Typhimurium are predicted to belong to the class of thiosulfate sulfurtransferases, enzymes that traffic sulfur between molecules. In the present study we demonstrated that the two genes contribute to S. Typhimurium virulence, as a glpE and pspE double deletion strain showed significantly decreased virulence in a mouse model of systemic infection. However, challenge of cultured epithelial cells and macrophages did not reveal any virulence-associated phenotypes. We hypothesized that their contribution to virulence could be in sulfur metabolism or by contributing to resistance to nitric oxide, oxidative stress, or cyanide detoxification. In vitro studies demonstrated that glpE but not pspE was important for resistance to H₂O₂. Since the double mutant, which was the one affected in virulence, was not affected in this assay, we concluded that resistance to oxidative stress and the virulence phenotype was most likely not linked. The two genes did not contribute to nitric oxid stress, to synthesis of essential sulfur containing amino acids, nor to detoxification of cyanide. Currently, the precise mechanism by which they contribute to virulence remains elusive.     

Leveraging substrate flexibility and product selectivity of acetogens in two‐stage systems for chemical production

Carbon dioxide (CO₂) stands out as sustainable feedstock for developing a circular carbon economy whose energy supply could be obtained by boosting the production of clean hydrogen from renewable electricity. H₂‐dependent CO₂ gas fermentation using acetogenic microorganisms offers a viable solution of increasingly demonstrated value. While gas fermentation advances to achieve commercial process scalability, which is currently limited to a few products such as acetate and ethanol, it is worth taking the best of the current state‐of‐the‐art technology by its integration within innovative bioconversion schemes. This review presents multiple scenarios where gas fermentation by acetogens integrate into double‐stage biotechnological production processes that use CO₂ as sole carbon feedstock and H₂ as energy carrier for products'' synthesis. In the integration schemes here reviewed, the first stage can be biotic or abiotic while the second stage is biotic. When the first stage is biotic, acetogens act as a biological platform to generate chemical intermediates such as acetate, formate and ethanol that become substrates for a second fermentation stage. This approach holds the potential to enhance process titre/rate/yield metrics and products'' spectrum. Alternatively, when the first stage is abiotic, the integrated two‐stage scheme foresees, in the first stage, the catalytic transformation of CO₂ into C₁ products that, in the second stage, can be metabolized by acetogens. This latter scheme leverages the metabolic flexibility of acetogens in efficient utilization of the products of CO₂ abiotic hydrogenation, namely formate and methanol, to synthesize multicarbon compounds but also to act as flexible catalysts for hydrogen storage or production.

Carbon dioxide recycling is a compelling need and microbial carbon dioxide fixation in value‐added compounds is a valuable opportunity. Fermentation of CO₂ gas streams using acetogenic bacteria is consolidating as a key biotechnology to move toward a cyclic carbon economy. Throughout the review, we pinpointed an ample range of products that are technically attainable by reframing a CO₂‐based gas fermentation process within a two‐stage context with the aim of highlighting some avenues available for fruitful exploitation of the current technology.     

Induction of Autophagy by Cystatin C: A Mechanism That Protects Murine Primary Cortical Neurons and Neuronal Cell Lines

Cystatin C (CysC) expression in the brain is elevated in human patients with epilepsy, in animal models of neurodegenerative conditions, and in response to injury, but whether up-regulated CysC expression is a manifestation of neurodegeneration or a cellular repair response is not understood. This study demonstrates that human CysC is neuroprotective in cultures exposed to cytotoxic challenges, including nutritional-deprivation, colchicine, staurosporine, and oxidative stress. While CysC is a cysteine protease inhibitor, cathepsin B inhibition was not required for the neuroprotective action of CysC. Cells responded to CysC by inducing fully functional autophagy via the mTOR pathway, leading to enhanced proteolytic clearance of autophagy substrates by lysosomes. Neuroprotective effects of CysC were prevented by inhibiting autophagy with beclin 1 siRNA or 3-methyladenine. Our findings show that CysC plays a protective role under conditions of neuronal challenge by inducing autophagy via mTOR inhibition and are consistent with CysC being neuroprotective in neurodegenerative diseases. Thus, modulation of CysC expression has therapeutic implications for stroke, Alzheimer''s disease, and other neurodegenerative disorders.