Identification of defensive antimicrobial compounds from environmental Serratia marcescens SNB-CN88 strain associated with macro-holobiont (termite nest) using a molecular network approach

International audienceEnvironmental microbes are an underexploited resource for the discovery of bioactive compounds. An integrated approach combining reversed-phase high-performance liquid chromatography and high-resolution tandem mass spectrometry with the use of molecular networks was applied to annotate novel chemical structures with potential antimicrobial activities. This metabolomic approach coupled with biological screening of environmental strains allowed the identification of 22 compounds, including 11 glucosamine derivatives and 10 cyclopeptides, from a bacterial strain of Serratia marcescens. Three new glucosamine derivatives and two stephensiolides were annotated. Two antibacterial stephensiolides, named stephensiolides E and F, were isolated to confirm annotations

Antiparasitic Ovalicin Derivatives from Pseudallescheria boydii, a Mutualistic Fungus of French Guiana Termites

International audienceSocial insects are in mutualism with microorganisms, contributing to their resistance against infectious diseases. The fungus Pseudallescheria boydii SNB-CN85 isolated from termites produces ovalicin derivatives resulting from the esterification of the less hindered site of the ovalicin epoxide by long-chain fatty acids. Their structures were elucidated using spectroscopic analysis and semisynthesis from ovalicin. For ovalicin, these compounds displayed antiprotozoal activities against Plasmodium falciparum and Trypanosoma brucei, with IC50 values of 19.8 and 1.1 µM, respectively, for the most active compound, i.e., ovalicin linoleate. In parallel, metabolomic profiling of a collection of P. boydii strains associated with termites made it possible to highlight this class of compounds together with tyroscherin derivatives in all strains. Finally, the complete genome of P. boydii strains was obtained by sequencing, and the cluster of potential ovalicin and ovalicin biosynthesis genes was annotated. Through these metabolomic and genomic analyses, a new ovalicin derivative named boyden C, in which the 6-membered ring of ovalicin was opened by oxidative cleavage, was isolated and structurally characterized

A New Safety Concern for Glaucoma Treatment Demonstrated by Mass Spectrometry Imaging of Benzalkonium Chloride Distribution in the Eye, an Experimental Study in Rabbits

<div><p>We investigated in a rabbit model, the eye distribution of topically instilled benzalkonium_(BAK) chloride a commonly used preservative in eye drops using mass spectrometry imaging. Three groups of three New Zealand rabbits each were used: a control one without instillation, one receiving 0.01%BAK twice a day for 5 months and one with 0.2%BAK one drop a day for 1 month. After sacrifice, eyes were embedded and frozen in tragacanth gum. Serial cryosections were alternately deposited on glass slides for histological (hematoxylin-eosin staining) and immunohistological controls (CD45, RLA-DR and vimentin for inflammatory cell infiltration as well as vimentin for Müller glial cell activation) and ITO or stainless steel plates for MSI experiments using Matrix-assisted laser desorption ionization time-of-flight. The MSI results were confirmed by a round-robin study on several adjacent sections conducted in two different laboratories using different sample preparation methods, mass spectrometers and data analysis softwares. BAK was shown to penetrate healthy eyes even after a short duration and was not only detected on the ocular surface structures, but also in deeper tissues, especially in sensitive areas involved in glaucoma pathophysiology, such as the trabecular meshwork and the optic nerve areas, as confirmed by images with histological stainings. CD45-, RLA-DR- and vimentin-positive cells increased in treated eyes. Vimentin was found only in the inner layer of retina in normal eyes and increased in all retinal layers in treated eyes, confirming an activation response to a cell stress. This ocular toxicological study confirms the presence of BAK preservative in ocular surface structures as well as in deeper structures involved in glaucoma disease. The inflammatory cell infiltration and Müller glial cell activation confirmed the deleterious effect of BAK. Although these results were obtained in animals, they highlight the importance of the safety-first principle for the treatment of glaucoma patients.</p> </div

MALDI-TOF imaging of whole eye section of a control rabbit.

<p>MALDI-TOF imaging shows the absence of benzalkonium chloride (BAK) in the control eye. (a) Histology image of an adjacent cryosection stained with hematoxylin-eosin (HE) showing three areas of interest: cornea (area 1), nasal iridocorneal angle (area 2) and near to the optic nerve (area 3). (b, c) Overlays between HE and MALDI-TOF images of BAK C₁₂ and C₁₄ eye distributions at <i>m/z</i> 304.32 and 332.36, respectively. Intensities of the ions are represented in colour, based on the intensity scale provided (from black to white). Field of view 18× 6 mm. (d, e, f) MALDI-TOF mass spectra extracted from areas 1, 2 and 3, respectively confirming the absence of BAK C₁₂ and C₁₄.</p