Marta Abrantes

Impact of manganese, copper and zinc ions on the transcriptome of the nosocomial pathogen Enterococcus faecalis V583

Mechanisms that enable Enterococcus to cope with different environmental stresses and their contribution to the switch from commensalism to pathogenicity of this organism are still poorly understood. Maintenance of intracellular homeostasis of metal ions is crucial for survival of these bacteria. In particular Zn2+, Mn2+ and Cu2+ are very important metal ions as they are co-factors of many enzymes, are involved in oxidative stress defense and have a role in the immune system of the host. Their concentrations inside the human body vary hugely, which makes it imperative for Enterococcus to fine-tune metal ion homeostasis in order to survive inside the host and colonize it. Little is known about metal regulation in Enterococcus faecalis. Here we present the first genome-wide description of gene expression of E. faecalis V583 growing in the presence of high concentrations of zinc, manganese or copper ions. The DNA microarray experiments revealed that mostly transporters are involved in the responses of E. faecalis to prolonged exposure to high metal concentrations although genes involved in cellular processes, in energy and amino acid metabolisms and genes related to the cell envelope also seem to play important roles.

Photoprotective Bioactivity Present in a Unique Marine Bacteria Collection from Portuguese Deep Sea Hydrothermal Vents

Interesting biological activities have been found for numerous marine compounds. In fact, screening of phylogenetically diverse marine microorganisms from extreme environments revealed to be a rational approach for the discovery of novel molecules with relevant bioactivities for industries such as pharmaceutical and cosmeceutical. Nevertheless, marine sources deliverables are still far from the expectations and new extreme sources of microbes should be explored. In this work, a marine prokaryotic collection from four Mid-Atlantic Ridge (MAR) deep sea hydrothermal vents near the Azores Islands, Portugal, was created, characterized and tested for its photoprotective capacity. Within 246 isolates, a polyphasic approach, using chemotaxonomic and molecular typing methods, identified 23-related clusters of phenetically similar isolates with high indexes of diversity. Interestingly, 16S rRNA gene sequencing suggested the presence of 43% new prokaryotic species. A sub-set of 139 isolates of the prokaryotic collection was selected for biotechnological exploitation with 484 bacterial extracts prepared in a sustainable upscalling manner. 22% of the extracts showed an industrially relevant photoprotective activity, with two extracts, belonging to new strains of the species Shewanella algae and Vibrio fluvialis, uniquely showing UV-A, UV-B and UV-C protective capacity. This clearly demonstrates the high potential of the bacteria MAR vents collection in natural product synthesis with market applications.

Use of MoO2Cl2(DMF)2 as a precursor for molybdate promoted hydrolysis of phosphoester bonds

Phosphoester bond cleavage of para-nitrophenylphosphate (pNPP), a commonly used model substrate, is accelerated by using the complex MoO(2)Cl(2)(DMF)(2) (1) (DMF = dimethylformamide) as a hydrolysis promoting agent, even when catalytic amounts of 1 (10 mol% relative to pNPP) are used. The reactions were performed under mild conditions (37-75 °C) and followed by (1)H NMR spectroscopy. For assays performed with high amounts of 1 (1000 mol% relative to pNPP), a white solid (2) precipitates during the initial stages of the reaction, which subsequently dissolves, leading eventually to the precipitation of a less soluble yellow solid (3). Taken together, the characterization data for 2 (FT-IR spectroscopy, elemental analysis, (1)H and (13)C NMR, and electrospray ionization mass spectrometry) indicate that it is a polymeric material with the formula Mo(2)O(6)(DMF)(n) and a structure comprising infinite isopolyoxomolybdate chains built up from edge-shared {MoO(6)} octahedra. Compound 3 was identified as the Keggin-type phosphomolybdate [(CH(3))(2)NH(2)](3)PMo(12)O(40). The formation of 3 is explained by the reaction of inorganic phosphate ions with isopolymolybdate species derived from 2, with dimethylammonium ions arising from the degradation of DMF. Both 2 and 3 are active for phosphoester bond hydrolysis with conversion profiles comparable to the ones obtained with the precursor 1.

Epoxidation of olefins catalyzed by molybdenum–siloxane compounds☆

Abstract The triphenylsiloxy complex MoO2(OSiPh3)2 and a related polyhedral metallasiloxane formulated as [MoO2(O2SiPh2)]n have been tested as catalysts for the liquid phase epoxidation of cyclic olefins by tert-butylhydroperoxide at 55 °C. The initial activities increased in the order 1-octene

Application of an indenyl molybdenum dicarbonyl complex in the isomerisation of α-pinene oxide to campholenic aldehyde

The complex [{(η5-Ind)Mo(CO)2(μ-Cl)}2] (1) has been tested for the industrially relevant catalytic isomerisation of α-pinene oxide (PinOx) to campholenic aldehyde (CPA) in the liquid phase. PinOx conversion and CPA selectivity are strongly influenced by the solvent employed. Complete conversion of PinOx was achieved within 1 min at 55 °C or 30 min at 35 °C using 1,2-dichloroethane as solvent, giving CPA in 68% yield. Other products included trans-carveol, iso-pinocamphone and trans-pinocarveol. The stability of 1 under the reaction conditions used was investigated by using FT-IR spectroscopy and electrospray ionisation mass spectrometry (ESI-MS) to characterise recovered solids. In the presence of air/moisture 1 undergoes oxidative decarbonylation upon dissolution to give oxomolybdenum species that are proposed to include a tetranuclear oxomolybdenum(V) complex. Conversely, ESI-MS studies of 1 dissolved in dry acetonitrile show mononuclear species of the type [IndMo(CO)2(CH3CN)n]+. The crystal structure of the ring-slipped dicarbonyl complex [(η3-Ind)Mo(CO)2Cl(CH3CN)2] (2) (obtained after dissolution of 1 in acetonitrile) is reported.

Enterococcus faecalis zinc-responsive proteins mediate bacterial defence against zinc overload, lysozyme and oxidative stress

Two Enterococcus faecalis genes encoding the P-type ATPase EF1400 and the putative SapB protein EF0759 were previously shown to be strongly upregulated in the presence of high concentrations of zinc. In the present work, we showed that a Zn(2+)-responsive DNA-binding motif (zim) is present in the promoter regions of these genes. Both proteins were further studied with respect to their involvement in zinc homeostasis and invasion of the host. EF0759 contributed to intramacrophage survival by an as-yet unknown mechanism(s). EF1400, here renamed ZntAEf, is an ATPase with specificity for zinc and plays a role in dealing with several host defences, i.e. zinc overload, oxidative stress and lysozyme; it provides E. faecalis cells with the ability to survive inside macrophages. As these three host defence mechanisms are important at several sites in the host, i.e. inside macrophages and in saliva, this work suggested that ZntAEf constitutes a crucial E. faecalis defence mechanism that is likely to contribute to the ability of this bacterium to endure life inside its host.

An Organotin Vanadate with Sodalite Topology and Catalytic Versatility in Oxidative Transformations

The new coordination polymer formulated as [Et3SnVO3] (1) has been synthesized and shown by a combined single‐crystal and synchrotron powder X‐ray diffraction structural analysis, supported by solid‐state NMR, to possess a three‐dimensional network structure with the sodalite topology, formed by tetravanadate polyanions, [V4O12]4−, that are linked by Et3Sn+ spacers. The catalytic versatility of compound 1 for liquid phase organic reactions was demonstrated by applying it for the epoxidation of olefins, the oxidative dehydrogenation of alcohols, and the oxidation of benzyl alcohol to benzaldehyde and benzoic acid, using tert‐butyl hydroperoxide (TBHP) as oxidant. Compound 1 acts a solid reservoir for soluble, catalytically active species, which promote high selectivities to the epoxide and carbonyl (aldehyde/ketone/acid) products. The epoxidation activity compares favorably with those reported for other organotin molybdate, tungstate and vanadate coordination polymers, and is superior to that displayed by the starting materials used for its synthesis (Et3SnBr and NH4VO3) and the metavanadate NBu4VO3.

Molybdenum oxide/bipyridine hybrid materials: synthesis, structure and catalytic studies

C435 crystal structure of human T-protein with folate cofactor and provided the insight into the molecular basis of the disease-causing mutations. Here we present the crystal structure of Escherichia coli T-protein in complex with dihydrolipoate-bearing H-protein and 5-methyltetrahydrofolate (5CH3-THF): a complex mimicking the ternary complex in the reverse reaction. The structure of the complex shows a highly interacting intermolecular interface limited to a small area and the protein-bound dihydrolipoyllysine arm inserted into the active site cavity of the Tprotein. Among the residues contributing to the interface, invariant Arg292 of the T-protein plays a key role in the complex assembly and probably in recruiting the aminomethyllipoyllysine arm to the active site of T-protein. It has been speculated that the aminomethyltransfer reaction from aminomethyllipoate of H-intermediate to THF is initiated by the direct attack of the methylene carbon atom by the nucleophilic N5 or N10 atoms of THF bound to T-protein accompanying the release of ammonia. However, the distances between the tip of the dihydrolipoyllysine arm and the methyl carbon atom of 5-CH3THF observed in the complex structure suggests the presence of an intermediary mediating the transfer reaction rather than the direct interaction. The hydrogen bond network surrounding the S8 atom of the dihydrolipoyllysine including invariant Asp96, Asp97, Asn113, and Arg223 of T-protein suggests that the reversible transfer of the methylene group between the lipoate and tetrahydrofolate should proceed through the electron relay-assisted iminium intermediate formation. Based on the structural observations together with mutational analyses, we propose a possible mechanism for T-protein catalysis. The structure also provides novel insights in understanding the disease-causing mutations, in addition to the disease-related impairment in the cofactor-enzyme interactions presented previously.