Estelle Morvan

Bacillus subtilis is widely studied in the microbial secondary metabolite (SM) field due to its rich variety of important natural products and genetic tractability. We report a pigment observed in B. subtilis soil isolate MB9_B4 on certain media. We characterize the conditions where this pigment is produced and identify the corresponding biosynthetic gene cluster (BGC) using a comparative genomic approach exploiting our strain collection containing other isolates with pigment production ability. The responsible BGC carried several genes, which were annotated as parts of the tryptophan biosynthesis pathway, possibly originating from duplication and divergence of originally primary metabolism. Identification of the pigment gene cluster additionally led to the discovery of additional pigment BGC carrier B. subtilis isolates, some of which were described at the earliest in 1896 under the name Bacillus aterrimus , referring to a characteristic dark pigmentation (the Latin “aterrimus” meaning very black). In addition, we employed solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopies to characterize the chemical groups of the pigment. This study describes the chemical and biological features of a new class of SM BGC, which we hope will serve to improve the current BGC discovery pipelines in Bacilli . IMPORTANCE: Identification of novel microbial secondary metabolites (SMs) and their biosynthetic gene cluster (BGC) has become increasingly difficult, especially in Bacilli , as the tools for screening and genome mining are dependent on clear function or similarity to already known BGCs. Pigments are SMs identified by their absorption of visible light, resulting in a certain color perceived by our eyes at sufficient concentrations. Thereby, pigments provide evidence of a BGC without knowing the sequence or function. Expanding the known repertoire of SM BGCs with novel BGCs will further reinforce the identification of a broader set of BGCs by mining tools such as antiSMASH.

A perforated silica layer with structural correlation is engineered using sol–gel chemistry, applied to large-scale flat and curved surfaces.

Aromatische Seitenketten sind wichtige Indikatoren für die Plastizität von Proteinen und bilden oft entscheidende Kontakte bei Protein‐Protein‐Wechselwirkungen. Wir untersuchten aromatische Reste in den beiden strukturell homologen cross‐β Amyloidfibrillen HET‐s und HELLF mit Hilfe eines spezifischen Ansatzes zur Isotopenmarkierung und Festkörper NMR mit Drehung am magischen Winkel. Das dynamische Verhalten der aromatischen Reste Phe und Tyr deutet darauf hin, dass der hydrophobe Amyloidkern starr ist und keine Anzeichen von “atmenden Bewegungen” auf einer Zeitskala von Hunderten von Millisekunden zeigt. Aromatische Reste, die exponiert an der Fibrillenoberfläche sitzen, haben zwar eine starre Ringachse, weisen aber Ringflips auf verschiedenen Zeitskalen von Nanosekunden bis Mikrosekunden auf. Unser Ansatz bietet einen direkten Einblick in die Bewegungen des hydrophoben Kerns und ermöglicht eine bessere Bewertung der Konformationsheterogenität, die aus einem NMR‐Strukturensemble einer solchen Cross‐β‐Amyloidstruktur hervorgeht.

Aromatic side chains are important reporters of the plasticity of proteins, and often form important contacts in protein–protein interactions. We studied aromatic residues in the two structurally homologous cross‐β amyloid fibrils HET‐s, and HELLF by employing a specific isotope‐labeling approach and magic‐angle‐spinning NMR. The dynamic behavior of the aromatic residues Phe and Tyr indicates that the hydrophobic amyloid core is rigid, without any sign of “breathing motions” over hundreds of milliseconds at least. Aromatic residues exposed at the fibril surface have a rigid ring axis but undergo ring flips on a variety of time scales from nanoseconds to microseconds. Our approach provides direct insight into hydrophobic‐core motions, enabling a better evaluation of the conformational heterogeneity generated from an NMR structural ensemble of such amyloid cross‐β architecture.

While establishing an invasive infection, the dormant conidia of Aspergillus fumigatus transit through swollen and germinating stages, to form hyphae. During this morphotype transition, the conidial cell wall undergoes dynamic remodeling, which poses challenges to the host immune system and antifungal drugs. However, such cell wall reorganization during conidial germination has not been studied so far. Here, we explored the molecular rearrangement of Aspergillus fumigatus cell wall polysaccharides during different stages of germination. We took advantage of magic-angle spinning NMR to investigate the cell wall polysaccharides, without employing any destructive method for sample preparation. The breaking of dormancy was associated with a significant change in the molar ratio between the major polysaccharides β-1,3-glucan and α-1,3-glucan, while chitin remained equally abundant. The use of various polarization transfers allowed the detection of rigid and mobile polysaccharides; the appearance of mobile galactosaminogalactan was a molecular hallmark of germinating conidia. We also report for the first time highly abundant triglyceride lipids in the mobile matrix of conidial cell walls. Water to polysaccharides polarization transfers revealed an increased surface exposure of glucans during germination, while chitin remained embedded deeper in the cell wall, suggesting a molecular compensation mechanism to keep the cell wall rigidity. We complement the NMR analysis with confocal and atomic force microscopies to explore the role of melanin and RodA hydrophobin on the dormant conidial surface. Exemplified here using Aspergillus fumigatus as a model, our approach provides a powerful tool to decipher the molecular remodeling of fungal cell walls during their morphotype switching.

The conformational strain diversity characterizing α-synuclein (α-syn) amyloid fibrils is thought to determine the different clinical presentations of neurodegenerative diseases underpinned by a synucleinopathy. Experimentally, various α-syn fibril polymorphs have been obtained from distinct fibrillization conditions by altering the medium constituents and were selected by amyloid monitoring using the probe thioflavin T (ThT). We report that, concurrent with classical ThT-positive products, fibrillization in saline also gives rise to polymorphs invisible to ThT (τ⁻). The generation of τ⁻ fibril polymorphs is stochastic and can skew the apparent fibrillization kinetics revealed by ThT. Their emergence has thus been ignored so far or mistaken for fibrillization inhibitions/failures. They present a yet undescribed atomic organization and show an exacerbated propensity toward self-replication in cortical neurons, and in living mice, their injection into the substantia nigra pars compacta triggers a synucleinopathy that spreads toward the dorsal striatum, the nucleus accumbens, and the insular cortex.

Human nuclear membrane (hNM) invaginations are thought to be crucial in fusion, fission and remodeling of cells and present in many human diseases. There is however little knowledge, if any, about their lipid composition and dynamics. We therefore isolated nuclear envelope lipids from human kidney cells, analyzed their composition and determined the membrane dynamics after resuspension in buffer. The hNM lipid extract was composed of a complex mixture of phospholipids, with high amounts of phosphatidylcholines, phosphatidylinositols (PI) and cholesterol. hNM dynamics was determined by solid-state NMR and revealed that the lamellar gel-to-fluid phase transition occurs below 0 °C, reflecting the presence of elevated amounts of unsaturated fatty acid chains. Fluidity was higher than the plasma membrane, illustrating the dual action of Cholesterol (ordering) and PI lipids (disordering). The most striking result was the large magnetic field-induced membrane deformation allowing to determine the membrane bending elasticity, a property related to hydrodynamics of cells and organelles. Human Nuclear Lipid Membranes were at least two orders of magnitude more elastic than the classical plasma membrane suggesting a physical explanation for the formation of nuclear membrane invaginations.