Existence of non-algebraic singularities of differential equation

An algebraizable singularity is a germ of a singular holomorphic foliation which can be defined in some appropriate local chart by a differential equation with algebraic coefficients. We show that there exists at least countably many saddle-node singularities of the complex plane that are not algebraizable.Comment: 11 page

Biochars from various biomass types as anodes for sodium-ion batteries

Until now, the applications targeted for biochars have mostly been focused in the field of energy, as combustion fuel, or of agronomy, as soil amendment. However, high-added value materials in the field of electrochemistry are now more and more mentioned as promising applications to investigate (Deng et al. 2016). At the moment, one major topic in electrochemistry is the development of alternative to lithium-ion battery in order to solve the issue of lithium supply. One of the most mature options is sodium-ion battery (Wang et al. 2016). In such battery, anode is generally made up of hard carbon, that has surface area below 10 m2.g-1 and subnanometric pores. Please click on the file below for full content of the abstract

On the Risks of Phylogeny-Based Strain Prioritization for Drug Discovery: Streptomyces lunaelactis as a Case Study

peer reviewedStrain prioritization for drug discovery aims at excluding redundant strains of a collection in order to limit the repetitive identification of the same molecules. In this work, we wanted to estimate what can be unexploited in terms of the amount, diversity, and novelty of compounds if the search is focused on only one single representative strain of a species, taking Streptomyces lunaelactis as a model. For this purpose, we selected 18 S. lunaelactis strains taxonomically clustered with the archetype strain S. lunaelactis MM109T. Genome mining of all S. lunaelactis isolated from the same cave revealed that 54% of the 42 biosynthetic gene clusters (BGCs) are strain specific, and five BGCs are not present in the reference strain MM109T. In addition, even when a BGC is conserved in all strains such as the bag/fev cluster involved in bagremycin and ferroverdin production, the compounds produced highly differ between the strains and previously unreported compounds are not produced by the archetype MM109T. Moreover, metabolomic pattern analysis uncovered important profile heterogeneity, confirming that identical BGC predisposition between two strains does not automatically imply chemical uniformity. In conclusion, trying to avoid strain redundancy based on phylogeny and genome mining information alone can compromise the discovery of new natural products and might prevent the exploitation of the best naturally engineered producers of specific molecules

Révélation du métabolisme spécialisé de Streptomyces lunaelactis spp.

The decline in the number of new antibiotics discoveries, related in parallel with an acceleration and generalization of the bacterial resistance phenomenon, the unfolding of the global health crisis, linked to the emergence of new viral pandemics, as well as the agro-industrial needs for new natural products less impacting the environment and human health, are examples of current driving elements that encourage research of new natural products. Over the past ten years or so, technological innovations allowing on one hand, the high-throughput and low-cost sequencing of bacterial genomes, and on the other, the high-resolution detection and identification of compounds, have offered an unmatched framework for discovery. During last decade, many innovative strategies have emerged, with the aim of providing access to biomolecules buried in nature. One of them is the bioprospecting of new microorganisms in ecological niches, described as extreme and so far unexplored, in order to maximize the chances of discovering new biomolecules. Streptomyces are soil bacteria, which actively participate in the recycling of organic biomass, and are also known to have an extremely developed secondary metabolism. Indeed, these Actinobacteria provide more than 50% of natural molecules of microbial origin used in human or animal medicine (antibacterial, antifungal, anti-tumor, etc) and in agro-industry (herbicides, insecticides, etc). The search for microorganisms native to karstic habitat called moonmilk, has led to the discovery of new strains of Streptomyces, including the recently described Streptomyces lunaelactis species. The aim of this work is to characterize the specialized metabolome associated with the Streptomyces lunaelactis species, including identification of the molecules produced by this microorganism and determination of the genes responsible for their biosynthesis. Through a comparative metabologenomic approach using 18 bacterial strains belonging to the S. lunaelactis species, this work has revealed their ability to produce bioactive molecules. Accordingly, the results of genome mining study of S. lunaelactis, combined with metabolomics studies, made it possible to evaluate the genetic predispositions of this species to produce specialized metabolites, as well as to experimentally validate some of these predictions. This work provides an overview on this species’ specialized metabolome and confirms that not only this microorganism, but also other Streptomyces derived from moonmilk, are abundant sources of new natural products. In addition, this work also exposes the risks associated with the dereplication of bacterial strain banks and investigates an innovative approach, which focuses on the evaluation of biosynthetic potential of strains within a single species, which shows a great promise in the search for new natural products.Unveiling the specialized metabolism of Streptomyces lunaelactis spp

Expertise mécanique des sciages par analyses des vibrations dans le domaine acoustique

AIX-MARSEILLE1-Inst.Médit.tech (130552107) / SudocAIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Structure of New Ferroverdins Recruiting Unconventional Ferrous Iron Chelating Agents

Ferroverdins are ferrous iron (Fe2+)-nitrosophenolato complexes produced by a few Streptomyces species as a response to iron overload. Previously, three ferroverdins were identified: ferroverdin A, in which three molecules of p-vinylphenyl-3-nitroso-4-hydroxybenzoate (p-vinylphenyl-3,4-NHBA) are recruited to bind Fe2+, and Ferroverdin B and Ferroverdin C, in which one molecule of p-vinylphenyl-3,4-NHBA is substituted by hydroxy-p-vinylphenyl-3,4-NHBA, and by carboxy-p-vinylphenyl-3,4-NHBA, respectively. These molecules, especially ferroverdin B, are potent inhibitors of the human cholesteryl ester transfer protein (CETP) and therefore candidate hits for the development of drugs that increase the serum concentration of high-density lipoprotein cholesterol, thereby diminishing the risk of atherosclerotic cardiovascular disease. In this work, we used high-resolution mass spectrometry combined with tandem mass spectrometry to identify 43 novel ferroverdins from the cytosol of two Streptomyces lunaelactis species. For 13 of them (designated ferroverdins C2, C3, D, D2, D3, E, F, G, H, CD, DE, DF, and DG), we could elucidate their structure, and for the other 17 new ferroverdins, ambiguity remains for one of the three ligands. p-formylphenyl-3,4-NHBA, p-benzoic acid-3,4-NHBA, 3,4-NHBA, p-phenylpropionate-3,4-NHBA, and p-phenyacetate-3,4-NHBA were identified as new alternative chelators for Fe2+-binding, and two compounds (C3 and D3) are the first reported ferroverdins that do not recruit p-vinylphenyl-3,4-NHBA. Our work thus uncovered putative novel CETP inhibitors or ferroverdins with novel bioactivities

Isolation, Characterization, and Antibacterial Activity of Hard-to-Culture Actinobacteria from Cave Moonmilk Deposits

Cave moonmilk deposits host an abundant and diverse actinobacterial population that has a great potential for producing novel natural bioactive compounds. In our previous attempt to isolate culturable moonmilk-dwelling Actinobacteria, only Streptomyces species were recovered, whereas a metagenetic study of the same deposits revealed a complex actinobacterial community including 46 actinobacterial genera in addition to streptomycetes. In this work, we applied the rehydration-centrifugation method to lessen the occurrence of filamentous species and tested a series of strategies to achieve the isolation of hard-to-culture and rare Actinobacteria from the moonmilk deposits of the cave “Grotte des Collemboles”. From the “tips and tricks” that were tested, separate autoclaving of the components of the International Streptomyces Project (ISP) medium number 5 (ISP5) medium, prolonged incubation time, and dilution of the moonmilk suspension were found to most effectively improve colony forming units. Taxonomic analyses of the 40 isolates revealed new representatives of the Agromyces, Amycolatopsis, Kocuria, Micrococcus, Micromonospora, Nocardia, and Rhodococcus species, as well as additional new streptomycetes. The applied methodologies allowed the isolation of strains associated with both the least and most abundant moonmilk-dwelling actinobacterial operational taxonomic units. Finally, bioactivity screenings revealed that some isolates displayed high antibacterial activities, and genome mining uncovered a strong potential for the production of natural compounds