Non-Saccharomyces Killer Toxins: Possible Biocontrol Agents Against Brettanomyces in Wine?

Red wine spoiled by the yeast Brettanomyces bruxellensis is characterised by off-odours commonlydescribed as horse sweat, phenolic, varnish and band-aid. The growth of this yeast in wine is traditionallycontrolled by the use of sulphur dioxide (SO2). However, the concentration of SO2, the pH of the wine,the presence of SO2-binding chemical compounds in the wine, as well as the strain of B. bruxellensis,determine the effectiveness of SO2. Other chemical preservatives have been tested, but are not much moreefficient than SO2, and methods used to clean barrels are only partially effective. Filtration of wine andthe use of electric currents/fields are also reported to alter the physical and sensory properties of wine. Inthis context, alternative methods are currently sought to achieve full control of this yeast in wine. Killertoxins have recently been proposed to fulfil this purpose. They are antimicrobial compounds secretedby Saccharomyces and non-Saccharomyces yeasts, displaying killer activity against other yeasts andfilamentous fungi. They are believed to play a role in yeast population dynamics, and this killer phenotypepotentially could be exploited to inhibit the growth of undesired microorganisms within a microbialecosystem such as that occurring in wine. In this review, non-Saccharomyces killer toxins are describedand their potential application in inhibiting B. bruxellensis in wine is discussed in comparison to othertried methods and techniques

A Shotgun Metagenomic Sequencing Exploration of Cabernet Sauvignon Grape Must Reveals Yeast Hydrolytic Enzymes

Shotgun sequencing was employed to explore the community structure (phylotyping of rRNA genes) andfunctional potential of Cabernet Sauvignon grape must microbiome. A metagenomic library, representing92.6 Mb of genetic information, was generated from DNA obtained from Cabernet Sauvignon grapemust.. Fungi were identified as the dominant domain (59.5%) followed by Streptophyta (39%). Amongthe 84 fungal species, 22 were yeasts of various genera. Additionally, grapevine endophytes such asDavidiella sp., Botryotinia fuckeliana, Alternaria sp., and Cladosporium sp. were identified. An unusuallyhigh prevalence of Mucor spp. was evidenced. Functional annotation revealed sequences of genesinvolved in metabolism (35.6%), followed by poorly characterized categories (28.3%), cellular processesand signalling (18.4%), and finally information storage (17.8%). Among the former, glycosidases wereabundant followed by glycogen debranching enzyme, 6-phosphofructokinase and trehalose-6-phosphatesynthase. Furthermore, the taxonomic analysis of the functional sequence data exhibited the eukaryoticgene pool that predominantly contains sequences derived from Streptophyta (mainly Vitis vinifera) 60% >Ascomycota (32%) > Basidiomycota (5%) > Bacteria (2.5%). Finally, sequences of a variety of hydrolyticenzymes of potential oenological relevance were retrieved, thereby confirming that grape juice is a richreservoir for valuable biocatalysts that should be explored further

Kinetic-Ion Simulations Addressing Whether Ion Trapping Inflates Stimulated Brillouin Backscattering Reflectivities

An investigation of the possible inflation of stimulated Brillouin backscattering (SBS) due to ion kinetic effects is presented using electromagnetic particle simulations and integrations of three-wave coupled-mode equations with linear and nonlinear models of the nonlinear ion physics. Electrostatic simulations of linear ion Landau damping in an ion acoustic wave, nonlinear reduction of damping due to ion trapping, and nonlinear frequency shifts due to ion trapping establish a baseline for modeling the electromagnetic SBS simulations. Systematic scans of the laser intensity have been undertaken with both one-dimensional particle simulations and coupled-mode-equations integrations, and two values of the electron-to-ion temperature ratio (to vary the linear ion Landau damping) are considered. Three of the four intensity scans have evidence of SBS inflation as determined by observing more reflectivity in the particle simulations than in the corresponding three-wave mode-coupling integrations with a linear ion-wave model, and the particle simulations show evidence of ion trapping.Comment: 56 pages, 20 figure

The production of reduced-alcohol wines using Gluzyme Mono® 10.000 BG-treated grape juice

High alcohol wines have become a major challenge in the international wine trade. Several physical processes areused to produce wines with reduced-alcohol content, all of which involve the selective extraction of ethanol basedon volatility or diffusion. In this study, the possibility of Gluzyme Mono® 10.000 BG (Gluzyme) (Novozymes, SouthAfrica) to reduce the glucose content of synthetic grape juice before fermentation was investigated in order to producewine with reduced-alcohol content. Gluzyme is a glucose oxidase preparation from Aspergillus oryzae, currently usedin the baking industry. Glucose oxidase catalyses the oxidation of glucose to gluconic acid and hydrogen peroxide(H2O2) in the presence of molecular oxygen. Gluzyme was initially used in synthetic grape juice, where differentenzyme concentrations and factors influencing its efficiency were investigated under winemaking conditions. Theresults showed up to 0.5% v/v less alcohol at an enzyme concentration of 20 kU compared to the control samples.This reduction in alcohol was increased to 1 and 1.3% v/v alcohol at pH 3.5 and pH 5.5 respectively in aerated (8mg/L O2) synthetic grape juice using 30 kU enzyme. Secondly, Gluzyme was used to treat Pinotage grape mustbefore fermentation. Gluzyme-treated wines at 30 kU enzyme concentration after fermentation contained 0.68%v/v less alcohol than the control wines. A decrease in acetic acid concentration of the treated compared to controlwines was also observed

Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 μ\mum lasers

Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $\mu$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratio are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and C$^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.Comment: Accepted for publication in Physical Review Accelerators and Beam

Effects of Ion-Ion Collisions and Inhomogeneity in Two-Dimensional Kinetic Ion Simulations of Stimulated Brillouin Backscattering

Two-dimensional simulations with the BZOHAR [B.I. Cohen, B.F. Lasinski, A.B. Langdon, and E.A. Williams, Phys. Plasmas 4, 956 (1997)] hybrid code (kinetic particle ions and Boltzmann fluid electrons) have been used to investigate the saturation of stimulated Brillouin backscatter (SBBS) instability including the effects of ion-ion collisions and inhomogeneity. Ion-ion collisions tend to increase ion-wave dissipation, which decreases the gain exponent for stimulated Brillouin backscattering; and the peak Brillouin backscatter reflectivities tend to decrease with increasing collisionality in the simulations. Two types of Langevin-operator, ion-ion collision models were implemented in the simulations. In both models used the collisions are functions of the local ion temperature and density, but the collisions have no velocity dependence in the first model. In the second model, the collisions are also functions of the energy of the ion that is being scattered so as to represent a Fokker-Planck collision operator. Collisions decorrelate the ions from the acoustic waves in SBS, which disrupts ion trapping in the acoustic wave. Nevertheless, ion trapping leading to a hot ion tail and two-dimensional physics that allows the SBS ion waves to nonlinearly scatter remain robust saturation mechanisms for SBBS in a high-gain limit over a range of ion collisionality. SBS backscatter in the presence of a spatially nonuniform plasma flow is also investigated. Simulations show that depending on the sign of the spatial gradient of the flow relative to the backscatter, ion trapping effects that produce a nonlinear frequency shift can enhance (auto-resonance) or decrease (anti-auto-resonance) reflectivities in agreement with theoretical arguments

Fast-ignition design transport studies: realistic electron source, integrated PIC-hydrodynamics, imposed magnetic fields

Transport modeling of idealized, cone-guided fast ignition targets indicates the severe challenge posed by fast-electron source divergence. The hybrid particle-in-cell [PIC] code Zuma is run in tandem with the radiation-hydrodynamics code Hydra to model fast-electron propagation, fuel heating, and thermonuclear burn. The fast electron source is based on a 3D explicit-PIC laser-plasma simulation with the PSC code. This shows a quasi two-temperature energy spectrum, and a divergent angle spectrum (average velocity-space polar angle of 52 degrees). Transport simulations with the PIC-based divergence do not ignite for > 1 MJ of fast-electron energy, for a modest 70 micron standoff distance from fast-electron injection to the dense fuel. However, artificially collimating the source gives an ignition energy of 132 kJ. To mitigate the divergence, we consider imposed axial magnetic fields. Uniform fields ~50 MG are sufficient to recover the artificially collimated ignition energy. Experiments at the Omega laser facility have generated fields of this magnitude by imploding a capsule in seed fields of 50-100 kG. Such imploded fields are however more compressed in the transport region than in the laser absorption region. When fast electrons encounter increasing field strength, magnetic mirroring can reflect a substantial fraction of them and reduce coupling to the fuel. A hollow magnetic pipe, which peaks at a finite radius, is presented as one field configuration which circumvents mirroring.Comment: 16 pages, 17 figures, submitted to Phys. Plasma

Neutron time-of-flight measurements of charged-particle energy loss in inertial confinement fusion plasmas

Neutron spectra from secondary ^{3}H(d,n)α reactions produced by an implosion of a deuterium-gas capsule at the National Ignition Facility have been measured with order-of-magnitude improvements in statistics and resolution over past experiments. These new data and their sensitivity to the energy loss of fast tritons emitted from thermal ^{2}H(d,p)^{3}H reactions enable the first statistically significant investigation of charged-particle stopping via the emitted neutron spectrum. Radiation-hydrodynamic simulations, constrained to match a number of observables from the implosion, were used to predict the neutron spectra while employing two different energy loss models. This analysis represents the first test of stopping models under inertial confinement fusion conditions, covering plasma temperatures of k_{B}T≈1-4  keV and particle densities of n≈(12-2)×10^{24}  cm^{-3}. Under these conditions, we find significant deviations of our data from a theory employing classical collisions whereas the theory including quantum diffraction agrees with our data