Wall Polymers Research Articles

Sb(III)-resistance mechanisms of a novel bacterium from non-ferrous metal tailings

Understanding the mechanism(s) of microbial resistance to antimony (Sb) is critical in the bioremediation of Sb polluted environments. Here a novel bacterium (Acinetobacter sp. JH7) isolated from mine tailings decreased the Microtox toxicity of a Sb(III)-containing medium. DNA sequencing and physiological testing were employed for the identification and characterization of strain JH7. Following a batch experiment, Fourier transform infrared spectroscopy (FTIR) and antimony speciation analyses determined the adsorption and oxidation of antimony. Analyses of Sb(III) distribution revealed that extracellular polymeric substances and cell walls inhibited Sb(III) entry into JH7 cells. FTIR studies indicated that key functional groups including –OH, C–N, and C–O likely participated in Sb(III) biosorption. Isothermal and kinetic studies revealed that Sb(III) sorption to viable JH7 cells fitted the Langmuir model (R2 = 0.99) and could be described by pseudo-second order kinetics (R2 = 0.99). Furthermore, the increase of anti-oxidative enzymatic activity of JH7 enhanced the intracellular detoxification of Sb(III), which would indirectly contribute to the Sb(III) resistance ability of strain JH7. Our results indicate that biosorption and ROS oxidation of Sb(III) were likely responsible for the decreased toxicity of Sb. The greater understanding how Acinetobacter sp. JH7 lowers the environmental Sb(III) toxicity could provide a basis for future research and subsequent development of technologies for the remediation of Sb contaminated sites.

Quantum dots are conventionally applicable for wide-profiling of wall polymer distribution and destruction in diverse cells of rice

Plant cell walls represent enormous biomass resources for biofuels, and it thus becomes important to establish a sensitive and wide-applicable approach to visualize wall polymer distribution and destruction during plant growth and biomass process. Despite quantum dots (QDs) have been applied to label biological specimens, little is reported about its application in plant cell walls. Here, semiconductor QDs (CdSe/ZnS) were employed to label the secondary antibody directed to the epitopes of pectin or xylan, and sorted out the optimal conditions for visualizing two polysaccharides distribution in cell walls of rice stem. Meanwhile, the established QDs approach could simultaneously highlight wall polysaccharides and lignin co-localization in different cell types. Notably, this work demonstrated that the QDs labeling was sensitive to profile distinctive wall polymer destruction between alkali and acid pretreatments with stem tissues of rice. Hence, this study has provided a powerful tool to characterize wall polymer functions in plant growth and development in vivo, as well as their distinct roles during biomass process in vitro.

Lrg1 Regulates β (1,3)-Glucan Masking in Candida albicans through the Cek1 MAP Kinase Pathway.

Candida albicans is among the most prevalent opportunistic human fungal pathogens. The ability to mask the immunogenic polysaccharide β (1,3)-glucan from immune detection via a layer of mannosylated proteins is a key virulence factor of C. albicans We previously reported that hyperactivation of the Cek1 mitogen-activated protein (MAP) kinase pathway promotes β (1,3)-glucan exposure. In this communication, we report a novel upstream regulator of Cek1 activation and characterize the impact of Cek1 activity on fungal virulence. Lrg1 encodes a GTPase-activating protein (GAP) that has been suggested to inhibit the GTPase Rho1. We found that disruption of LRG1 causes Cek1 hyperactivation and β (1,3)-glucan unmasking. However, when GTPase activation was measured for a panel of GTPases, the lrg1ΔΔ mutant exhibited increased activation of Cdc42 and Ras1 but not Rho1 or Rac1. Unmasking and Cek1 activation in the lrg1ΔΔ mutant can be blocked by inhibition of the Ste11 MAP kinase kinase kinase (MAPKKK), indicating that the lrg1ΔΔ mutant acts through the canonical Cek1 MAP kinase cascade. In order to determine how Cek1 hyperactivation specifically impacts virulence, a doxycycline-repressible hyperactive STE11ΔN467 allele was expressed in C. albicans In the absence of doxycycline, this allele overexpressed STE11ΔN467 , which induced production of proinflammatory tumor necrosis factor alpha (TNF-α) from murine macrophages. This in vitro phenotype correlates with decreased colonization and virulence in a mouse model of systemic infection. The mechanism by which Ste11ΔN467 causes unmasking was explored with RNA sequencing (RNA-Seq) analysis. Overexpression of Ste11ΔN467 caused upregulation of the Cph1 transcription factor and of a group of cell wall-modifying proteins which are predicted to impact cell wall architecture.IMPORTANCECandida albicans is an important source of systemic infections in humans. The ability to mask the immunogenic cell wall polymer β (1,3)-glucan from host immune surveillance contributes to fungal virulence. We previously reported that the hyperactivation of the Cek1 MAP kinase cascade promotes cell wall unmasking, thus increasing strain immunogenicity. In this study, we identified a novel regulator of the Cek1 pathway called Lrg1. Lrg1 is a predicted GTPase-activating protein (GAP) that represses Cek1 activity by downregulating the GTPase Cdc42 and its downstream MAPKKK, Ste11. Upregulation of Cek1 activity diminished fungal virulence in the mouse model of infection, and this correlates with increased cytokine responses from macrophages. We also analyzed the transcriptional profile determined during β (1,3)-glucan exposure driven by Cek1 hyperactivation. Our report provides a model where Cek1 hyperactivation causes β (1,3)-glucan exposure by upregulation of cell wall proteins and leads to more robust immune detection in vivo, promoting more effective clearance.

P‐10.3: Research and Analysis of Polymer Walls Technologies for Flexible Display

We studied the effects of photomask design, illumination time, and UV intensity on the formation of polymer walls, and speculated the related mechanism. According to the optimized condition, we make a flexible LCD cell with colorless polyimide substrate.

Reaction of gum arabic samples with monoclonal antibodies directed to plant cell wall polymers in dot immunobinding

Certain plant cell wall constituents have been found in gum samples derived from Acacia trees, thus analytical techniques for the determination of these plant cell wall components in any media can be applied in the analysis of the physico-chemical properties of these gums. In this experiment, gum samples harvested from various Acacia trees grown in different African countries were subjected to a dot immunobinding reaction using a panel of anti-plant cell wall directed monoclonal antibodies since the gum samples have been found to contain certain plant cell wall constituents. Five antiplant cell wall monoclonal antibodies, JIM 5, JIM 7, JIM 13, LM 6 and MAC 207 were reacted with fifteen gum Arabic samples 1 – 15 and water as control. The results showed that apart from reacting with the monoclonal antibodies, gum samples showed varying degrees of reactivity with the monoclonal antibodies. JIM 5 indicated no reaction with any of the gum samples, whereas JIM 7, JIM 13, LM 6 and MAC 207 exhibited reactions with the samples. The results suggest that, anti-plant cell wall directed monoclonal antibodies can be used as a tool to distinguish between gum Arabic samples from different tree species, as well as from different African countries. Thus, a testing kit which is easy to use and cheaper to acquire can be developed using anti-plant cell wall monoclonal antibodies, to improve quality control in the current gum trade.

Kinetics of Water Vapor Sorption in Wood Cell Walls: State of the Art and Research Needs

Water vapor sorption is the most fundamental aspect of wood-moisture relations. It is directly or indirectly related to the physical properties of wood and the onset of wood-damage mechanisms. While sorption properties of cellulosic materials have been utilized since antiquity, the time-dependent transition from one moisture content to another (i.e., sorption kinetics) has received much less attention. In this critical review, we present the state-of-the-art of water vapor sorption kinetics in wood. We first examine different experimental methods that have been used to measure sorption kinetics, from the quartz helix vacuum balance beginning in earnest in the 1930s, to automated sorption balances used recently. We then give an overview of experimental observations and describe the physical phenomena that occur during the sorption process, which potentially govern the following kinetics: boundary layer mass transfer resistance, heat of sorption, cell wall diffusion, swelling, and polymer mobility. Finally, we evaluate theoretical models that have been proposed for describing sorption kinetics, considering both experimental data and the physical processes described in the previous section. It is clear that no previously developed model can phenomenologically describe the sorption process. Instead, new models are needed. We conclude that the development of new models will require more than simple gravimetric measurements. In addition to mass changes, complementary techniques are needed to probe other important physical quantities on multiple length scales.

The Dynamics of the Cell Wall Proteome of Developing Alfalfa Stems.

In this study, the cell-wall-enriched subproteomes at three different heights of alfalfa stems were compared. Since these three heights correspond to different states in stem development, a view on the dynamics of the cell wall proteome during cell maturation is obtained. This study of cell wall protein-enriched fractions forms the basis for a description of the development process of the cell wall and the linking cell wall localized proteins with the evolution of cell wall composition and structure. The sequential extraction of cell wall proteins with CaCl2, EGTA, and LiCl-complemented buffers was combined with a gel-based proteome approach and multivariate analysis. Although the highest similarities were observed between the apical and intermediate stem regions, the proteome patterns are characteristic for each region. Proteins that bind carbohydrates and have proteolytic activity, as well as enzymes involved in glycan remobilization, accumulate in the basal stem region. Beta-amylase and ferritin likewise accumulate more in the basal stem segment. Therefore, remobilization of nutrients appears to be an important process in the oldest stem segment. The intermediate and apical regions are sites of cell wall polymer remodeling, as suggested by the high abundance of proteins involved in the remodeling of the cell wall, such as xyloglucan endoglucosylase, beta-galactosidase, or the BURP-domain containing polygalacturonase non-catalytic subunit. However, the most striking change between the different stem parts is the strong accumulation of a DUF642-conserved domain containing protein in the apical region of the stem, which suggests a particular role of this protein during the early development of stem tissues.

Spray-Drying Performance and Thermal Stability of L-Ascorbic Acid Microencapsulated with Sodium Alginate and Gum Arabic.

The potential of sodium alginate (ALG) and gum arabic (GA) as wall polymers for L-ascorbic acid (AA) encapsulation as a tool for their preservation against the thermo-oxidative degradation was investigated. The influence of such polymers used as wall material on the AA-content, size, encapsulation efficiency, encapsulation yield and thermo-oxidative stability were evaluated. The AA-microparticles were obtained using the spray-drying technique. An experimental Taguchi design was employed to assess the influence of the variables in the encapsulation process. The microparticles morphology and size distribution were characterized by scanning electron microscopy and laser diffraction. The thermal stability of AA microparticles was studied by differential scanning calorimetry and thermogravimetry analysis. This work points out the viability to encapsulate AA using GA and ALG through a spray-drying process. In general, a product yield ranging from 35.1% to 83.2% and an encapsulation efficiency above 90% were reached. Spherical microparticles with a smooth surface were obtained with a mean diameter around 6 μm and 9 μm for the those prepared with GA and ALG, respectively. The thermo-oxidative analysis showed that both polymers allow maintaining AA stable up to 188 °C, which is higher than the traditional processing temperature used in the fish feed industry.

Multi-Scale Evaluation of the Effect of Phenol Formaldehyde Resin Impregnation on the Dimensional Stability and Mechanical Properties of Pinus Massoniana Lamb.

The local chemistry and mechanics of the control and phenol formaldehyde (PF) resin modified wood cell walls were analyzed to illustrate the modification mechanism of wood. Masson pine (Pinus massoniana Lamb.) is most widely distributed in the subtropical regions of China. However, the dimensional instability and low strength of the wood limits its use. Thus, the wood was modified by PF resin at concentrations of 15%, 20%, 25%, and 30%, respectively. The density, surface morphology, chemical structure, cell wall mechanics, shrinking and swelling properties, and macro-mechanical properties of Masson pine wood were analyzed to evaluate the modification effectiveness. The morphology and Raman spectra changes indicated that PF resin not only filled in the cell lumens, but also penetrated into cell walls and interacted with cell wall polymers. The filling and diffusing of resin in wood resulted in improved dimensional stability, such as lower swelling and shrinking coefficients, an increase in the elastic modulus (Er) and hardness (H) of wood cell walls, the hardness of the transverse section and compressive strength of the wood. Both the dimensional stability and mechanical properties improved as the PF concentration increased to 20%; that is, a PF concentration of 20% may be preferred to modify Masson pine wood.

UMP Pyrophosphorylase: A Moonlighting Protein with Essential Functions in Chloroplast Development and Photosynthesis Establishment.

Pyrimidine nucleotides (e.g. deoxy-CTP, deoxy-TTP, UTP, and CTP) are essential building blocks for DNA and RNA synthesis in all organisms. In plants, Suc and cell wall polymer synthesis depend on pyrimidine nucleotide-derived substrates, such as UDP-Glc, and important classes of membrane lipids are

Pectin Chemistry and Cellulose Crystallinity Govern Pavement Cell Morphogenesis in a Multi-Step Mechanism.

Simple plant cell morphologies, such as cylindrical shoot cells, are determined by the extensibility pattern of the primary cell wall, which is thought to be largely dominated by cellulose microfibrils, but the mechanism leading to more complex shapes, such as the interdigitated patterns in the epidermis of many eudicotyledon leaves, is much less well understood. Details about the manner in which cell wall polymers at the periclinal wall regulate the morphogenetic process in epidermal pavement cells and mechanistic information about the initial steps leading to the characteristic undulations in the cell borders are elusive. Here, we used genetics and recently developed cell mechanical and imaging methods to study the impact of the spatio-temporal dynamics of cellulose and homogalacturonan pectin distribution during lobe formation in the epidermal pavement cells of Arabidopsis (Arabidopsis thaliana) cotyledons. We show that nonuniform distribution of cellulose microfibrils and demethylated pectin coincides with spatial differences in cell wall stiffness but may intervene at different developmental stages. We also show that lobe period can be reduced when demethyl-esterification of pectins increases under conditions of reduced cellulose crystallinity. Our data suggest that lobe initiation involves a modulation of cell wall stiffness through local enrichment in demethylated pectin, whereas subsequent increase in lobe amplitude is mediated by the stress-induced deposition of aligned cellulose microfibrils. Our results reveal a key role of noncellulosic polymers in the biomechanical regulation of cell morphogenesis.

Modulation of Charge Density and Charge Polarity of Nanopore Wall by Salt Gradient and Voltage.

Surface charge plays a very important role in biological processes including ionic and molecular transport across a cell membrane. Placement of charges and charge patterns on walls of polymer and solid-state nanopores allowed preparation of ion-selective systems as well as ionic diodes and transistors to be applied in building biological sensors and ionic circuits. In this article, we show that the surface charge of a 10 nm diameter silicon nitride nanopore placed in contact with a salt gradient is not a constant value, but rather it depends on applied voltage and magnitude of the salt gradient. We found that even when a nanopore was in contact with solutions of pH equivalent to the isoelectric point of the pore surface, the pore walls became charged with voltage-dependent charge density. Implications of the charge gating for detection of proteins passing through a nanopore were considered, as well. Experiments performed with single 30 nm long silicon nitride nanopores were described by continuum modeling, which took into account the surface reactions on the nanopore walls and local modulation of the solution pH in the pore and at the pore entrances. The results revealed that manipulation of surface charge can occur without changing pH of the background electrolyte, which is especially important for applications where maintaining pH at a constant and physiological level is necessary. The system presented also offers a possibility to modulate polarity and magnitude of surface charges in a two-electrode setup, which previously was accomplished in more complex multielectrode systems.

Structural features in tension wood and distribution of wall polymers in the G-layer of in vitro grown poplars.

Under the effect of disturbances, like unbalanced stem, but also during normal development, poplar trees can develop a specific secondary xylem, called "tension wood" (TW), which is easily identifiable by the presence of a gelatinous layer in the secondary cell walls (SCW) of the xylem fibers. Since TW formation was mainly performed on 2-year-old poplar models, an in vitro poplar that produces gelatinous fibers (G-fibers) while offering the same experimental advantages as herbaceous plants has been developed. Using specific cell wall staining techniques, wood structural features and lignin/cellulose distribution were both detailed in cross-sections obtained from the curved stem part of in vitro poplars. A supposed delay in the SCW lignification process in the G-fibers, along with the presence of a G-layer, could be observed in the juvenile plants. Moreover, in this G-layer, the immunolabeling of various polymers carried out in the SCW of TW has allowed detecting crystalline cellulose, arabinogalactans proteins, and rhamnogalacturonans I; however, homogalacturonans, xylans, and xyloglucans could not be found. Interestingly, extensins were detected in this typical adaptative or stress-induced structure. These observations were corroborated by a quantitation of the immunorecognized polymer distribution using gold particle labeling. In conclusion, the in vitro poplar model seems highly convenient for TW studies focusing on the implementation of wall polymers that provide the cell wall with greater plasticity in adapting to the environment.

Formation of Polymer Walls through the Phase Separation of a Liquid Crystal Mixture Induced by a Spatial Elastic Energy Difference

We propose a method to form polymer walls without the use of a photomask in a liquid crystal (LC) cell by phase separation of an LC mixture induced by a spatial elastic energy difference. When an in-plane electric field is applied to a vertically aligned cell filled with a mixture of LC and a reactive monomer (RM), a high spatial elastic energy is induced along the direction perpendicular to the interdigitated electrodes. RMs move to the boundaries where the elastic energy is very high and an in-plane component of the applied electric field exists, which results in the phase separation of the LC/RM mixture. We have shown that we can form polymer walls by applying ultraviolet light irradiation to the LC cell. These polymer walls can function as alignment layers. We observed morphological patterns of the polymer structure through polarized optical microscopy, scanning electron microscopy, and atomic force microscopy. The polymer walls formed in an LC cell can affect the orientation of LCs in the lateral direction. Bistable switching of a polymer-walled cell could be achieved by using three-terminal electrodes where both vertical and in-plane electric fields can be applied. Vertical anchoring with the alignment layer on each substrate allows LC molecules to remain vertically aligned after removal of the applied vertical electric field. Furthermore, in-plane anchoring with the formed polymer walls allows the LC molecules to remain homogeneously aligned after removal of the applied in-plane electric field. The proposed method for the formation of polymer structures could be a useful tool to fabricate LC cells for various applications. As a bistable phase-grating device, the diffraction efficiency of a polymer-walled cell was comparable to that of a pure-LC cell. Its operating voltage was 44% lower than that of a pure-LC cell owing to in-plane anchoring provided by the polymer walls. Moreover, it can be operated with very low power because it does not require power to maintain the state. In addition, the total response time of a polymer-walled cell was approximately 68% shorter than that of a pure-LC cell because all switching was forcibly controlled by applying an electric field.

Enhanced Weathering Resistance of Radiata Pine Wood by Treatment with an Aqueous Styrene/Acrylic Acid Copolymer Dispersion

Radiata pine (Pinus radiata Don.) sapwood was treated with an aqueous dispersion solution of styrene/acrylic acid (St/AA) copolymer (5, 15, or 25%) and the treatment effect on weathering of wood was determined. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy suggested that the St/AA treatment delayed lignin degradation during artificial weathering; the protection effect increased with St/AA concentration. Decrease in water contact angle upon weathering for the treated wood was also slower than for the untreated control. Scanning electron microscopy revealed that the St/AA polymer filled some wood cell lumina, which facilitates to inhibit moisture and light (especially ultraviolet light) penetration into wood. During 12 months of outdoor exposure, the St/AA-treated wood boards had lower moisture content and less detachment of earlywood cells than the untreated controls. Treatments with St/AA stabilized the surface color by inhibiting photo-oxidation of cell wall polymers and propagation of staining fungi. The results suggest that treatment with St/AA can substantially improve wood’s resistance to weathering.

Cell Wall Polymer Composition and Spatial Distribution in Ripe Banana and Mango Fruit: Implications for Cell Adhesion and Texture Perception.

Banana (Musa acuminata) and mango (Mangifera indica) are two of the most popular fruits eaten worldwide. They both soften during ripening but their textural attributes are markedly different. This study aimed to elucidate the molecular mechanism underpinning textural differences between banana and mango. We used a novel combination of methods at different scales to analyse the surface properties of fruit cells and the potential contribution of cells and cell wall components to oral processing and texture perception. The results indicated that cell separation occurred easily in both organs under mild mechanical stress. Banana cells showed distinctively elongated shapes with distinct distribution of pectin and hemicellulose epitopes at the cell surface. In contrast, mango had relatively spherical cells that ruptured during cell separation. Atomic force microscopy detected soft surfaces indicative of middle lamella remnants on banana cells, while mango cells had cleaner, smoother surfaces, suggesting absence of middle lamellae and more advanced cell wall disassembly. Comparison of solubilized polymers by cell wall glycome analysis showed abundance of mannan and feruylated xylan in separation exudate from banana but not mango, but comparable levels of pectin and arabinogalactan proteins. Bulk rheology experiments showed that both fruits had similar apparent viscosity and hence might be extrapolated to have similar “oral thickness” perception. On the other hand, oral tribology experiments showed significant differences in their frictional behavior at orally relevant speeds. The instrumental lubrication behavior can be interpreted as “smooth” mouthfeel for mango as compared to “astringent” or “dry” for banana in the later stages of oral processing. The results suggest that cell wall surface properties contribute to lubricating behavior associated with textural perception in the oral phase.

Controlled release and targeting of polypeptide-deposited liposomes by enzymatic degradation

We prepared biobased nanocapsules with enzymatic degradability, which were generated by the layer-by-layer deposition of enzymes and polypeptide over the liposomal surface. Here, we demonstrate two different systems based on the enzymatic degradation of polymer layers. First, the deposition of trypsin and polyarginine (PArg), which is cleavable by trypsin, was carried out over a negatively charged liposome. The enzymatic cleavage of PArg resulted in exposure of the lipid membrane, which facilitated release of the cargo. Next, we attempted to degrade the outer polymer layer of the multilayered capsule wall to display the inner polymer layer by enzymatic degradation. This approach enabled the accumulation and targeting of the nanocapsules through the affinity between the displayed polymer layer and the target hydroxyapatite (HAp). The polymer wall was constructed with an inner layer consisting of poly-L-glutamic acid (PGlu) and an outer layer consisting of trypsin and PArg onto the liposome. The degradation of the outer PArg by trypsin allowed the surface to display the inner PGlu, which has bone-targeting ability. In addition, the polymer wall was constructed from an inner layer of PArg and an outer layer of pepsin and PGlu. The degradation of the outer PGlu by pepsin led to inner PArg on the surface to achieve cell-penetrating activity. We developed biobased nanocapsules with enzymatic degradability, which were generated by the layer-by-layer deposition of enzymes and polypeptide over a liposome. Our developed nanocapsules exhibited layer-specific degradation by enzymes, which enables the release of cargo through degradation of the capsule wall as well as accumulation and targeting of nanocapsules through the emergence of surface properties and functionalities such as bone-targeting ability and cell-penetrating ability by unveiling an inner polymer layer.

Poplar carbohydrate-active enzymes: whole-genome annotation and functional analyses based on RNA expression data.

SummaryCarbohydrate‐active enzymes (CAZymes) catalyze the formation and modification of glycoproteins, glycolipids, starch, secondary metabolites and cell wall biopolymers. They are key enzymes for the biosynthesis of food and renewable biomass. Woody biomass is particularly important for long‐term carbon storage and as an abundant renewable natural resource for many industrial applications. This study presents a re‐annotation of CAZyme genes in the current Populus trichocarpa genome assembly and in silico functional characterization, based on high‐resolution RNA‐Seq data sets. Altogether, 1914 CAZyme and expansin genes were annotated in 101 families. About 1797 of these genes were found expressed in at least one Populus organ. We identified genes involved in the biosynthesis of different cell wall polymers and their paralogs. Whereas similar families exist in poplar and Arabidopsis thaliana (with the exception of CBM13 found only in poplar), a few families had significantly different copy numbers between the two species. To identify the transcriptional coordination and functional relatedness within the CAZymes and other proteins, we performed co‐expression network analysis of CAZymes in wood‐forming tissues using the AspWood database (http://aspwood.popgenie.org/aspwood-v3.0/) for Populus tremula. This provided an overview of the transcriptional changes in CAZymes during the transition from primary to secondary wall formation, and the clustering of transcripts into potential regulons. Candidate enzymes involved in the biosynthesis of polysaccharides were identified along with many tissue‐specific uncharacterized genes and transcription factors. These collections offer a rich source of targets for the modification of secondary cell wall biosynthesis and other developmental processes in woody plants.

Advances in Imaging Plant Cell Walls.

Understanding of cell wall architecture, including the crosslinking of cell wall polymers, provides crucial information for elucidating the relationship between cell wall structure and cell function. Moreover, examination of the cell wall informs efforts to improve biomass breakdown in bioreactor conditions. Over the past decades, imaging techniques have been used extensively to reveal the structural organization and chemical composition of cell walls, but detailed imaging of the native composition and architecture of the cell wall remains challenging. Here, we review progress in the development of cell wall imaging techniques. In particular, we focus on several advanced, label-free techniques for imaging cell walls and their potential applications in investigation of the biological functions of plant cell walls.

Grape pomace fermentation and cell wall degradation by Kluyveromyces marxianus Y885

Kluyveromyces marxianus Y885, an endopolygalacturonase (EPG) producing yeast, was evaluated for its capacity to hydrolyse the cell wall polymers of grape pomace as well as its general fermentation capabilities on this substrate. Small scale batch fermentations on autoclaved pomace inoculated with Y885 delivered 10 g/l ethanol and 7.7 g/l glycerol, the latter 14% more than a commercial wine yeast strain. When comparing the hydrolysis of the pomace cell wall by the Kluyveromyces EPG with that of a commonly used pectolytic commercial enzyme preparation, the polymer analysis confirmed that both the Y885 EPG and the commercial enzyme preparation primarily degraded surface exposed pectin polymers, while the hemicellulose-cellulose backbone was unchanged. High levels of galacturonic acid (GalA) monomers were generated by the commercial enzyme, whereas the Y885 EPG mostly liberated (polymeric) GalA-containing fragments together with low quantities of monomers. The Y885 strain produced strong pectinase activity throughout the fermentation process, whereas pectinolytic activity levels rapidly declined for the commercial enzyme after addition. The data obtained shows the evolution of pectin degradation during fermentation and provide compelling evidence that Y885 can utilise/valorise the grape pomace, and that the secreted enzymes (including an EPG) can effectively unravel the structural components of the grape cell walls.