Potential Application of Yeast Cell Wall Biopolymers as Probiotic Encapsulants

Biopolymers of yeast cell walls, such as β-glucan, mannoprotein, and chitin, may serve as viable encapsulants for probiotics. Due to its thermal stability, β-glucan is a suitable cryoprotectant for probiotic microorganisms during freeze-drying. Mannoprotein has been shown to increase the adhesion of probiotic microorganisms to intestinal epithelial cells. Typically, chitin is utilized in the form of its derivatives, particularly chitosan, which is derived via deacetylation. Brewery waste has shown potential as a source of β-glucan that can be optimally extracted through thermolysis and sonication to yield up to 14% β-glucan, which can then be processed with protease and spray drying to achieve utmost purity. While laminarinase and sodium deodecyle sulfate were used to isolate and extract mannoproteins and glucanase was used to purify them, hexadecyltrimethylammonium bromide precipitation was used to improve the amount of purified mannoproteins to 7.25 percent. The maximum chitin yield of 2.4% was attained by continuing the acid-alkali reaction procedure, which was then followed by dialysis and lyophilization. Separation and purification of yeast cell wall biopolymers via diethylaminoethyl (DEAE) anion exchange chromatography can be used to increase the purity of β-glucan, whose purity in turn can also be increased using concanavalin-A chromatography based on the glucan/mannan ratio. In the meantime, mannoproteins can be purified via affinity chromatography that can be combined with zymolase treatment. Then, dialysis can be continued to obtain chitin with high purity. β-glucans, mannoproteins, and chitosan-derived yeast cell walls have been shown to promote the survival of probiotic microorganisms in the digestive tract. In addition, the prebiotic activity of β-glucans and mannoproteins can combine with microorganisms to form synbiotics.

The antifungal potential of the chelating agent EDTA against postharvest plant pathogen Botrytis cinerea

Botrytis cinerea is a phytopathogenic fungus that causes gray mold, a major postharvest disease of fruits and vegetables. Chemical fungicides remain the main solution to control Botrytis disease, but concerns have raised about their safety to environment and human health, and there is an increasing need for development of more effective and less toxic treatments. In this study the divalent cation chelating agent ethylenediaminetetraacetic acid (EDTA) exhibited marked antifungal activity against B. cinerea, including inhibition of spore germination, mycelial growth, infection cushion formation, stimulation of cell death, and impairment of fungal virulence. These adverse effects of EDTA could be reversed by the addition of calcium ion, implying that metal ion chelation is involved in the fungicidal mechanism. Bean leaf and tomato fruit protection assay indicated that EDTA treatment led to a significant reduction of infection by B. cinerea. Furthermore, the antifungal activity of EDTA was significantly enhanced when used in combination with fenhexamid. These findings suggest that EDTA could be a promising tool to control B. cinerea, and application of EDTA may reduce the use of conventional chemical fungicides.

Modulation of the cell wall protein Ecm33p in yeast Saccharomyces cerevisiae improves the production of small metabolites

The cell wall is a dynamic organelle that determines the shape and provides the cell with mechanical strength. This study investigated whether modulation of cell wall composition can influence the production or secretion of small metabolites by yeast cell factories. We deleted and upregulated several cell wall-related genes KRE2, CWP1, CWP2, ECM33, PUN1, and LAS21 in yeast Saccharomyces cerevisiae engineered for p-coumaric acid or β-carotene production. Deletions of las21∆ and ecm33∆ impaired the yeast growth on medium with cell wall stressors, calcofluor white, and caffeine. Both overexpression and deletion of ECM33 significantly improved the specific yield of p-coumaric acid and β-carotene. We observed no change in secretion in any cell wall altered mutants, suggesting the cell wall is not a limiting factor for small molecule secretion at the current production levels. We evaluated the cell wall morphology of the ECM33 mutant strains using transmission electron microscopy. The ecm33∆ mutants had an increased chitin deposition and a less structured cell wall, while the opposite was observed in ECM33-overexpressing strains. Our results point at the cell wall-related gene ECM33 as a potential target for improving production in engineered yeast cell factories.

Simple and efficient isolation of plant genomic DNA using magnetic ionic liquids

BACKGROUND

Plant DNA isolation and purification is a time-consuming and laborious process relative to epithelial and viral DNA sample preparation due to the cell wall. The lysis of plant cells to free intracellular DNA normally requires high temperatures, chemical surfactants, and mechanical separation of plant tissue prior to a DNA purification step. Traditional DNA purification methods also do not aid themselves towards fieldwork due to the numerous chemical and bulky equipment requirements.

RESULTS

In this study, intact plant tissue was coated by hydrophobic magnetic ionic liquids (MILs) and ionic liquids (ILs) and allowed to incubate under static conditions or dispersed in a suspension buffer to facilitate cell disruption and DNA extraction. The DNA-enriched MIL or IL was successfully integrated into the qPCR buffer without inhibiting the reaction. The two aforementioned advantages of ILs and MILs allow plant DNA sample preparation to occur in one minute or less without the aid of elevated temperatures or chemical surfactants that typically inhibit enzymatic amplification methods. MIL or IL-coated plant tissue could be successfully integrated into a qPCR assay without the need for custom enzymes or manual DNA isolation/purification steps that are required for conventional methods.

CONCLUSIONS

The limited amount of equipment, chemicals, and time required to disrupt plant cells while simultaneously extracting DNA using MILs makes the described procedure ideal for fieldwork and lab work in low resource environments.

Method Development Progress in Genetic Engineering of Thraustochytrids

Thraustochytrids are unicellular, heterotrophic marine eukaryotes. Some species are known to store surplus carbon as intracellular lipids, and these also contain the long-chain polyunsaturated fatty acid docosahexaenoic acid (DHA). Most vertebrates are unable to synthesize sufficient amounts of DHA, and this fatty acid is essential for, e.g., marine fish, domesticated animals, and humans. Thraustochytrids may also produce other commercially valuable fatty acids and isoprenoids. Due to the great potential of thraustochytrids as producers of DHA and other lipid-related molecules, a need for more knowledge on this group of organisms is needed. This necessitates the ability to do genetic manipulation of the different strains. Thus far, this has been obtained for a few strains, while it has failed for other strains. Here, we systematically review the genetic transformation methods used for different thraustochytrid strains, with the aim of aiding studies on strains not yet successfully transformed. The designs of transformation cassettes are also described and compared. Moreover, the potential problems when trying to establish transformation protocols in new thraustochytrid species/strains are discussed, along with suggestions utilized in other organisms to overcome similar challenges. The approaches discussed in this review could be a starting point when designing protocols for other non-model organisms.

Branched amphotericin functional poly(N-isopropyl acrylamide): an antifungal polymer

Branched poly(N-isopropylacrylamide) was functionalized with Amphotericin B (AmB) at the chain ends to produce an antifungal material. The polymer showed antifungal properties against AmB-sensitive strains of Candida albicans, Fusarium keratoplasticum and Aspergillus flavus (minimal inhibitory concentration ranged from 5 to 500 µg ml^-1) but was not effective against an AmB resistant strain of C. albicans nor against Candida tropicalis. The polymer end groups bound to the AmB target, ergosterol, and the fluorescence spectrum of a dye used as a solvatochromic probe, Nile red, was blue shifted indicating that segments of the polymer became desolvated on binding. The polymer was less toxic to corneal and renal epithelial cells and explanted corneal tissue than the free drug. Also, the polymer did not induce reactive oxygen species release from peripheral blood mononuclear cells, nor did it cause a substantial release of the proinflammatory cytokines, tumour necrosis factor-α and interleukin-1β (at 0.5 mg ml^-1).

Fungal Extracellular Vesicles in Pathophysiology

Fungal pathogens are a concern in medicine and agriculture that has been exacerbated by the emergence of antifungal-resistant varieties that severely threaten human and animal health, as well as food security. This had led to the search for new and sustainable treatments for fungal diseases. Innovative solutions require a deeper understanding of the interactions between fungal pathogens and their hosts, and the key determinants of fungal virulence. Recently, a link has emerged between the release of extracellular vesicles (EVs) and fungal virulence that may contribute to finding new methods for fungal control. Fungal EVs carry pigments, carbohydrates, protein, nucleic acids and other macromolecules with similar functions as those found in EVs from other organisms, however certain fungal features, such as the fungal cell wall, impact EV release and cargo. Fungal EVs modulate immune responses in the host, have a role in cell-cell communication and transport molecules that function in virulence. Understanding the function of fungal EVs will expand our knowledge of host-pathogen interactions and may provide new and specific targets for antifungal drugs and agrichemicals.

Development of an Efficient Strategy to Improve Extracellular Polysaccharide Production of Ganoderma lucidum Using L-Phenylalanine as an Enhancer

Ganoderma lucidum has been a well-known species of basidiomycetes for a long time, and has been widely applied in the fields of food and medicine. Based on the simulation results of model iZBM1060 in our previous research, the effect of L-phenylalanine on G. lucidum extracellular polysaccharides (EPSs) was investigated in this study. EPS production reached 0.91 g/L at 0.4 g/L L-phenylalanine after a 24 h culture, which was 62.5% higher than that of control (0.56 g/L). Transcriptome and genome analysis showed that L-phenylalanine deaminase and benzoate 4-hydroxylase (related to L-phenylalanine metabolism) were significantly up-regulated, while the cell wall mannoprotein gene was down-regulated. Transmission electronic microscopy (TEM) and atomic force microscopy results showed that the cell wall thickness decreased by 58.58%, and cell wall porosity increased in cells treated with L-phenylalanine, which probably contribute to the increasing EPS production. This study provides an efficient strategy for fungal polysaccharide production with high output and low cost.

Localization and functional characterization of the pathogenesis-related proteins Rbe1p and Rbt4p in Candida albicans

Members of the Cysteine-rich secretory protein, Antigen 5 and Pathogenesis-related 1 (CAP) protein superfamily are important virulence factors in fungi but remain poorly characterized on molecular level. Here, we investigate the cellular localization and molecular function of Rbe1p and Rbt4p, two CAP family members from the human pathogen Candida albicans. We unexpectedly found that Rbe1p localizes to budding sites of yeast cells in a disulfide bond-dependent manner. Furthermore, we show that Rbe1p and Rbt4p bind free cholesterol in vitro and export cholesteryl acetate in vivo. These findings suggest a previously undescribed role for Rbe1p in cell wall-associated processes and a possible connection between the virulence attributes of fungal CAP proteins and sterol binding.

The Viscoelastic Properties of the Fungal Cell Wall Allow Traffic of AmBisome as Intact Liposome Vesicles

The fungal cell wall is a critically important structure that represents a permeability barrier and protective shield. We probed Candida albicans and Cryptococcus neoformans with liposomes containing amphotericin B (AmBisome), with or without 15-nm colloidal gold particles. The liposomes have a diameter of 60 to 80 nm, and yet their mode of action requires them to penetrate the fungal cell wall to deliver amphotericin B to the cell membrane, where it binds to ergosterol. Surprisingly, using cryofixation techniques with electron microscopy, we observed that the liposomes remained intact during transit through the cell wall of both yeast species, even though the predicted porosity of the cell wall (pore size, ~5.8 nm) is theoretically too small to allow these liposomes to pass through intact. C. albicans mutants with altered cell wall thickness and composition were similar in both their in vitro AmBisome susceptibility and the ability of liposomes to penetrate the cell wall. AmBisome exposed to ergosterol-deficient C. albicans failed to penetrate beyond the mannoprotein-rich outer cell wall layer. Melanization of C. neoformans and the absence of amphotericin B in the liposomes were also associated with a significant reduction in liposome penetration. Therefore, AmBisome can reach cell membranes intact, implying that fungal cell wall viscoelastic properties are permissive to vesicular structures. The fact that AmBisome can transit through chemically diverse cell wall matrices when these liposomes are larger than the theoretical cell wall porosity suggests that the wall is capable of rapid remodeling, which may also be the mechanism for release of extracellular vesicles.IMPORTANCE AmBisome is a broad-spectrum fungicidal antifungal agent in which the hydrophobic polyene antibiotic amphotericin B is packaged within a 60- to 80-nm liposome. The mode of action involves perturbation of the fungal cell membrane by selectively binding to ergosterol, thereby disrupting membrane function. We report that the AmBisome liposome transits through the cell walls of both Candida albicans and Cryptococcus neoformans intact, despite the fact that the liposome is larger than the theoretical cell wall porosity. This implies that the cell wall has deformable, viscoelastic properties that are permissive to transwall vesicular traffic. These observations help explain the low toxicity of AmBisome, which can deliver its payload directly to the cell membrane without unloading the polyene in the cell wall. In addition, these findings suggest that extracellular vesicles may also be able to pass through the cell wall to deliver soluble and membrane-bound effectors and other molecules to the extracellular space.

Turgor Pressure and Possible Constriction Mechanisms in Bacterial Division

Bacterial cytokinesis begins with the assembly of FtsZ into a Z ring at the center of the cell. The Z-ring constriction in Gram-negative bacteria may occur in an environment where the periplasm and the cytoplasm are isoosmotic, but in Gram-positive bacteria the constriction may have to overcome a substantial turgor pressure. We address three potential sources of invagination force. (1) FtsZ itself may generate force by curved protofilaments bending the attached membrane. This is sufficient to constrict liposomes in vitro. However, this force is on the order of a few pN, and would not be enough to overcome turgor. (2) Cell wall (CW) synthesis may generate force by pushing the plasma membrane from the outside. However, this would probably require some kind of Brownian ratchet to separate the CW and membrane sufficiently to allow a glycan strand to slip in. The elastic element is not obvious. (3) Excess membrane production has the potential to contribute significantly to the invagination force. If the excess membrane is produced under the CW, it would force the membrane to bleb inward. We propose here that a combination of FtsZ pulling from the inside, and excess membrane pushing membrane inward may generate a substantial constriction force at the division site. This combined force generation mechanism may be sufficient to overcome turgor pressure. This would abolish the need for a Brownian ratchet for CW growth, and would permit CW to operate by reinforcing the constrictions generated by FtsZ and excess membrane.

Vacuum facilitated infusion of bioactives into yeast microcarriers: Evaluation of a novel encapsulation approach

Encapsulation into yeast microcarriers provides an appealing alternative to biomimetic systems by employing natural, pre-formed vehicles for the stabilization and delivery of bioactives compounds. However, current (diffusion-limited) methods of encapsulation using yeast require long time scales and heating which lead to poor encapsulation efficiencies and yields. This study evaluates the usage of vacuum infusion to encapsulate two model bioactives, curcumin and fisetin, into yeast and yeast cell wall particles and the physical parameters, e.g. vacuum level, concentration of carrier solvent, log p value of bioactive, etc., which facilitate the process of vacuum infusion. Encapsulation efficiencies were determined using UV-vis spectrophotometry. Localization of bioactives within yeast microcarriers was determined using confocal and multiphoton (two-photon) microscopy. 99% vacuum, or 1.0kPa, and 35% ethanol (v/v) provide the optimal conditions for the encapsulation of both curcumin and fisetin; compared to the diffusion-limited method, vacuum infusion is able to encapsulate 3× more curcumin and 2× more fisetin into yeast microcarrier and requires 288-fold less time. Enhanced encapsulation efficiencies and yield as well as rapid encapsulation process technology presented in this study can transform the use of cell based carriers for encapsulation and delivery of bioactives.

Molecule structural factors influencing the loading of flavoring compounds in a natural-preformed capsule: Yeast cells

Yeast cells are efficient microcapsules for the encapsulation of flavoring compounds. However, as they are preformed capsules, they have to be loaded with the active. Encapsulation efficiency is to a certain level correlated with LogP. In this study, the effect of structural factors on the encapsulation of amphiphilic flavors was investigated. Homological series of carboxylic acids, ethyl esters, lactones, alcohols and ketones were encapsulated into the yeast Yarrowia lipolytica. Although, in a single homological series, the length of the molecule and thus the LogP were correlated with encapsulation efficiency (EY%), big differences were observable between series. For instance, carboxylic acids and lactones exhibited EY% around 45%-55%, respectively, for compounds bigger than C8 and C6, respectively, whereas ethyl esters reached only about 15-20% for C10 compounds. For a group of various C6-compounds, EY% varied from 4% for hexanal to 45% for hexanoic acid although the LogP of the two compounds was almost similar at 1.9. In total our results point out the importance of the level of polarity and localization of the polar part of the compound in addition to the global hydrophobicity of the molecule. They will be of importance to optimize the encapsulation of mixtures of compounds.

Hyperproduction of β-Glucanase Exg1 Promotes the Bioconversion of Mogrosides in Saccharomyces cerevisiae Mutants Defective in Mannoprotein Deposition

Bacteria and fungi can secrete extracellular enzymes to convert macromolecules into smaller units. Hyperproduction of extracellular enzymes is often associated with alterations in cell wall structure in fungi. Recently, we identified that Saccharomyces cerevisiae kre6Δ mutants can efficiently convert mogroside V into mogroside III E, which has antidiabetic properties. However, the underlying efficient bioconversion mechanism is unclear. In the present study, the mogroside (MG) bioconversion properties of several cell wall structure defective mutants were analyzed. We also compared the cell walls of these mutants by transmission electron microscopy, a zymolyase sensitivity test, and a mannoprotein release assay. We found zymolyase-sensitive mutants (including kre1Δ, las21Δ, gas1Δ, and kre6Δ), with defects in mannoprotein deposition, exhibit efficient MG conversion and excessive leakage of Exg1; such defects were not observed in wild-type cells, or mutants with abnormal levels of glucans in the cell wall. Thus, yeast mutants defective in mannoprotein deposition may be employed to convert glycosylated bioactive compounds.

Antibacterial Activity, in Vitro Cytotoxicity, and Cell Cycle Arrest of Gemini Quaternary Ammonium Surfactants

Twelve gemini quaternary ammonium surfactants have been employed to evaluate the antibacterial activity and in vitro cytotoxicity. The antibacterial effects of the gemini surfactants are performed on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) with minimum inhibitory concentrations (MIC) ranging from 2.8 to 167.7 μM. Scanning electron microscopy (SEM) analysis results show that these surfactants interact with the bacterial cell membrane, disrupt the integrity of the membrane, and consequently kill the bacteria. The data recorded on C6 glioma and HEK293 human kidney cell lines using an MTT assay exhibit low half inhibitory concentrations (IC50). The influences of the gemini surfactants on the cell morphology, the cell migration ability, and the cell cycle are observed through hematoxylin-eosin (HE) staining, cell wound healing assay, and flow cytometric analyses, respectively. Both the values of MIC and IC50 decrease against the growth of the alkyl chain length of the gemini surfactants with the same spacer group. In the case of surfactants 12-s-12, the MICs and IC50s are found to decrease slightly with the spacer chain length changing from 2 to 8 and again to increase at higher spacer length (s = 10-12). All of the gemini surfactants show great antibacterial activity and cytotoxicity, and they might exhibit potential applications in medical fields.

Covalently linked cell wall proteins of Candida albicans and their role in fitness and virulence

The cell wall of Candida albicans consists of an internal skeletal layer and an external protein coat. This coat has a mosaic-like nature, containing c. 20 different protein species covalently linked to the skeletal layer. Most of them are GPI proteins. Coat proteins vary widely in function. Many of them are involved in the primary interactions between C. albicans and the host and mediate adhesive steps or invasion of host cells. Others are involved in biofilm formation and cell-cell aggregation. They further include iron acquisition proteins, superoxide dismutases, and yapsin-like aspartic proteases. In addition, several covalently linked carbohydrate-active enzymes are present, whose precise functions remain hitherto largely elusive. The expression levels of the genes that encode covalently linked cell wall proteins (CWPs) can vary enormously. They depend on the mode of growth and the combined inputs of several signaling pathways that sense environmental conditions. This is reflected in the unusually long intergenic regions of most of these genes. Finally, the precise location of several covalently linked CWPs is temporally and spatially regulated. We conclude that covalently linked CWPs of C. albicans play a crucial role in fitness and virulence and that their expression is tightly controlled.

Dynamics of cell wall structure in Saccharomyces cerevisiae

The cell wall of Saccharomyces cerevisiae is an elastic structure that provides osmotic and physical protection and determines the shape of the cell. The inner layer of the wall is largely responsible for the mechanical strength of the wall and also provides the attachment sites for the proteins that form the outer layer of the wall. Here we find among others the sexual agglutinins and the flocculins. The outer protein layer also limits the permeability of the cell wall, thus shielding the plasma membrane from attack by foreign enzymes and membrane-perturbing compounds. The main features of the molecular organization of the yeast cell wall are now known. Importantly, the molecular composition and organization of the cell wall may vary considerably. For example, the incorporation of many cell wall proteins is temporally and spatially controlled and depends strongly on environmental conditions. Similarly, the formation of specific cell wall protein-polysaccharide complexes is strongly affected by external conditions. This points to a tight regulation of cell wall construction. Indeed, all five mitogen-activated protein kinase pathways in bakers' yeast affect the cell wall, and additional cell wall-related signaling routes have been identified. Finally, some potential targets for new antifungal compounds related to cell wall construction are discussed.