Sugar utilization patterns and respiro-fermentative metabolism in the baker’s yeast Torulaspora delbrueckii

The highly osmo- and cryotolerant yeast species Torulaspora delbrueckii is an important case study among the non-Saccharomyces yeast species. The strain T delbrueckii PYCC 532 1, isolated from traditional corn and rye bread dough in northern Portugal, is considered particularly interesting for the baking industry. This paper reports the sugar utilization patterns of this strain, using media with glucose, maltose and sucrose, alone or in mixtures. Kinetics of growth, biomass and ethanol yields, fermentation and respiration rates, hydrolase activities and sugar uptake rates were used to infer the potential applied relevance of this yeast in comparison to a conventional baker's strain of Saccharomyces cerevisiae. The results showed that both maltase and maltose transport in T delbrueckii were subject to glucose repression and maltose induction, whereas invertase was subject to glucose control but not dependent on sucrose induction. A comparative analysis of specific sugar consumption rates and transport capacities suggests that the transport step limits both glucose and maltose metabolism. Specific rates of CO2 production and O-2 consumption showed a significantly higher contribution of respiration to the overall metabolism in T delbrueckii than in S. cerevisiae. This was reflected in the biomass yields from batch cultures and could represent an asset for the large-scale production of the former species. This work contributes to a better understanding of the physiology of a non-conventional yeast species, with a view to the full exploitation of T delbrueckii by the baking industry.This work was partially funded by Agência de Inovação (AdI) program POCI2010/2.3, project ‘PARFERM’. C. A.-A. and A. P. were supported by PhD fellowships from PRAXIS XXI – BD/21543/99 and BD/13282/ 2003, respectively (Fundação para a Ciência e para a Tecnologia, Portugal).info:eu-repo/semantics/publishedVersio

Methyl-β-cyclodextrin Inclusion Complex with β‑Caryophyllene: Preparation, Characterization, and Improvement of Pharmacological Activities

β-Caryophyllene (BCP) is a sesquiterpene that shows high potential in pharmacological applications. However, these have been drastically limited by the respective volatility and poor water solubility. The present study investigates the formation of inclusion complexes between BCP and methyl-β-cyclodextrin (MβCD) and shows that these complexes promote a significant improvement of the anti-inflammatory, gastric protection, and antioxidant activities relative to neat BCP. It is shown that the solubility of BCP is significantly increased through complexation in phase solubility studies. Inclusion complexes with MβCD in solid state were prepared by three different methods, kneading, rotary evaporation, and lyophilization, with the latter confirmed by differential scanning calorimetry, Fourier transformed infrared spectroscopy, scanning electron microscopy, ¹H NMR spectroscopy, and molecular dynamics studies. This study provides for the first time a full characterization of inclusion complexes between BCP and MβCD and highlights the impact of complex formation upon pharmacological activity

Harvesting of Surfactant-Solubilized Asphaltenes by Magnetic Nanoparticles

Asphaltenes are a severe problem for the oil industry. The high content of aromatic and aliphatic hydrocarbons in asphaltenes poses a challenge for efficient methods of the solubilization and degradation of their components. The main goal of this study was to investigate an efficient and innovative method for asphaltene solubilization with surfactants to produce supramolecular aggregates with affinity by magnetic nanoparticles (Fe3O4) for magnetic separation and degradation. Asphaltene mixed with the cationic surfactant cetyltrimethylammonium bromide (CTAB) was both solubilized in chloroform and the solvent dried with N2 to produce a film that was resuspended in water and formed a stable colloid with asphaltene incorporated in CTAB micelles. The suspensions of CTAB/asphaltene supramolecular aggregates obtained at different surfactant/asphaltene ratios were characterized by dynamic and static light scattering (DLS and SLS) and by electrophoretic mobility for ζ potential determination. CTAB concentrations of 30 and 60 mM produced spherical supramolecular aggregates (SMAs) of size between 100 and 200 nm with polydispersity. The ζ potential of CTAB micelles loaded with asphaltenes increased from +9.17 +/– 4.6 to +56.7 +/– 5.8 eV. Electron paramagnetic resonance revealed that asphaltene forms stable free radicals in CTAB micelles. Classical molecular dynamics simulations were also used to study interactions of the functional groups of asphaltenes. The association with CTAB micelles provided the binding affinity of asphaltenes for nanoparticulate magnetite (Fe3O4) and precipitation of the most CTAB content. In this condition, Fe3O4 promoted the degradation of asphaltenes to low molecular mass products. Therefore, incorporation in CTAB micelles is a simple and innovative method contributing to asphaltene removal, degradation, and possible conversion to products with aggregated value

Structural and Kinetic Properties of the Aldehyde Dehydrogenase NahF, a Broad Substrate Specificity Enzyme for Aldehyde Oxidation

The salicylaldehyde dehydrogenase (NahF) catalyzes the oxidation of salicylaldehyde to salicylate using NAD⁺ as a cofactor, the last reaction of the upper degradation pathway of naphthalene in <i>Pseudomonas putida</i> G7. The naphthalene is an abundant and toxic compound in oil and has been used as a model for bioremediation studies. The steady-state kinetic parameters for oxidation of aliphatic or aromatic aldehydes catalyzed by 6xHis-NahF are presented. The 6xHis-NahF catalyzes the oxidation of aromatic aldehydes with large <i>k</i>_cat/<i>K</i>_m values close to 10⁶ M^–1 s^–1. The active site of NahF is highly hydrophobic, and the enzyme shows higher specificity for less polar substrates than for polar substrates, e.g., acetaldehyde. The enzyme shows α/β folding with three well-defined domains: the oligomerization domain, which is responsible for the interlacement between the two monomers; the Rossmann-like fold domain, essential for nucleotide binding; and the catalytic domain. A salicylaldehyde molecule was observed in a deep pocket in the crystal structure of NahF where the catalytic C284 and E250 are present. Moreover, the residues G150, R157, W96, F99, F274, F279, and Y446 were thought to be important for catalysis and specificity for aromatic aldehydes. Understanding the molecular features responsible for NahF activity allows for comparisons with other aldehyde dehydrogenases and, together with structural information, provides the information needed for future mutational studies aimed to enhance its stability and specificity and further its use in biotechnological processes

Excellent Catalytic Effects of Graphene Nanofibers on Hydrogen Release of Sodium alanate

One of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled devices and vehicles remains hydrogen storage. More environmentally friendly and effective nonmetal catalysts are required to improve hydrogen sorption. In this paper, through a combination of experiment and theory, we evaluate and explore the catalytic effects of layered graphene nanofibers toward hydrogen release of light metal hydrides such as sodium alanate. Graphene nanofibers, especially the helical kind, are found to considerably improve hydrogen release from NaAlH₄, which is of significance for the further enhancement of this practical material for environmentally friendly and effective hydrogen storage applications. Using density functional theory, we find that carbon sheet edges, regardless of whether they are of zigzag or armchair type, can weaken Al–H bonds in sodium alanate, which is believed to be due to a combination of NaAlH₄ destabilization and dissociation product stabilization. The helical form of graphene nanofibers, with larger surface area and curved configuration, appears to benefit the functionalization of carbon sheet edges. We believe that our combined experimental and theoretical study will stimulate more explorations of other microporous or mesoporous nanomaterials with an abundance of exposed carbon edges in the application of practical complex light metal hydride systems

ZEPLIN-II limits on WIMP-nucelon interactions

ZEPLIN II is a two‐phase xenon detector designed to detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs). Following the first 31‐day underground run in Boulby Mine, UK, the collaboration published dark matter limits in January 2007; the first such limits using two‐phase xenon technology. We outline the key detector design, performance and results here