Identification of yeast genes that confer resistance to chitosan oligosaccharide (COS) using chemogenomics

Applications of chitosan in the agri-food sector: A review

Chitosan is a natural and renewable polysaccharide that can form biopolymers. It is derived from the deacetylation of chitin mainly from crustaceans' shells, but also from fungi and insects. Thanks to unique characteristics such as antimicrobial effects, antioxidant properties or film forming capacities, it has triggered an important amount of research in the last decade about possible applications in industrial fields. The main application field of chitosan is the food industry where it can be used for preservation purposes and shelf-life improvement for fresh food products such as fruits or meat. For beverages, it is used for clarification and fining as well as elimination of spoilage flora in beverages like fruit juices or wine. And in agriculture, it can be used as a plant protection product through different mechanisms like the elicitation of plant defences. The mechanisms of action of chitosan on microorganisms are multiple and complex but revolve mostly around the disturbance of microorganisms' membranes and cell walls resulting in the leakage of cell material. The use of chitosan is still minor but is promising in finding environmentally friendly alternatives to synthetic chemicals and plastics. Therefore, its characterization is primordial for the future of sustainable production and preservation processes.

Cylindrospermopsin enhances the conjugative transfer of plasmid-mediated multi-antibiotic resistance genes through glutathione biosynthesis inhibition

Cylindrospermopsin (CYN), a cyanobacterial toxin, has been detected in the global water environment. However, information concerning the potential environmental risk of CYN is limited, since the majority of previous studies have mainly focused on the adverse health effects of CYN through contaminated drinking water. The present study reported that CYN at environmentally relevant levels (0.1-100 μg/L) can significantly enhance the conjugative transfer of RP4 plasmid in Escherichia coli genera, wherein application of 10 μg/L of CYN led to maximum fold change of ∼6.5- fold at 16 h of exposure. Meanwhile, evaluation of underlying mechanisms revealed that environmental concentration of CYN exposure could increase oxidative stress in the bacterial cells, resulting in ROS overproduction. In turn, this led to an upregulation of antioxidant enzyme-related genes to avoid ROS attack. Further, inhibition of the synthesis of glutathione (GSH) was also detected, which led to the rapid depletion of GSH in cells and thus triggered the SOS response and promoted the conjugative transfer process. Increase in cell membrane permeability, upregulation of expression of genes related to pilus generation, ATP synthesis, and RP4 gene expression were also observed. These results highlight the potential impact on the spread of antimicrobial resistance in water environments.

Exploring the mechanism underlying the antifungal activity of chitosan-based ZnO, CuO, and SiO2 nanocomposites as nanopesticides against Fusarium solani and Alternaria solani

Chitosan-based nanocomposites (CS NCs) are gaining considerable attention as multifaceted antifungal agents. This study investigated the antifungal activity of NCs against two phytopathogenic strains: Fusarium solani (F. solani) and Alternaria solani (A. solani). Moreover, it sheds light on their underlying mechanisms of action. The NCs, CS-ZnO, CS-CuO, and CS-SiO2, were characterized using advanced methods. Dynamic and electrophoretic light scattering techniques revealed their size range (60-170 nm) and cationic nature, as indicated by the positive zeta potential values (from +16 to +22 mV). Transmission electron microscopy revealed the morphology of the NCs as agglomerates formed between the chitosan and oxide components. X-ray diffraction patterns confirmed crystalline structures with specific peaks indicating their constituents. Antifungal assessments using the agar diffusion technique demonstrated significant inhibitory effects of the NCs on both fungal strains (1.5 to 4-fold), surpassing the performance of the positive control, nystatin. Notably, the NCs exhibited superior antifungal potency, with CS-ZnO NCs being the most effective. A. solani was the most sensitive strain to the studied agents. Furthermore, the tested NCs induced oxidative stress in fungal cells, which elevated stress biomarker levels, such as superoxide dismutase (SOD) activity and protein carbonyl content (PCC), 2.5 and 6-fold for the most active CS-CuO in F. solani respectively. Additionally, they triggered membrane lipid peroxidation up to 3-fold higher compared to control, a process that potentially compromises membrane integrity. Laurdan fluorescence spectroscopy highlighted alterations in the molecular organization of fungal cell membranes induced by the NCs. CS-CuO NCs induced a membrane rigidifying effect, while CS-SiO2 and CS-ZnO could rigidify membranes in A. solani and fluidize them in F. solani. In summary, this study provides an in-depth understanding of the interactions of CS-based NCs with two fungal strains, showing their antifungal activity and offering insights into their mechanisms of action. These findings emphasize the potential of these NCs as effective and versatile antifungal agents.

A Review of Chitosan and Chitosan Nanofiber: Preparation, Characterization, and Its Potential Applications

Chitosan is produced by deacetylating the abundant natural chitin polymer. It has been employed in a variety of applications due to its unique solubility as well as its chemical and biological properties. In addition to being biodegradable and biocompatible, it also possesses a lot of reactive amino side groups that allow for chemical modification and the creation of a wide range of useful derivatives. The physical and chemical characteristics of chitosan, as well as how it is used in the food, environmental, and medical industries, have all been covered in a number of academic publications. Chitosan offers a wide range of possibilities in environmentally friendly textile processes because of its superior absorption and biological characteristics. Chitosan has the ability to give textile fibers and fabrics antibacterial, antiviral, anti-odor, and other biological functions. One of the most well-known and frequently used methods to create nanofibers is electrospinning. This technique is adaptable and effective for creating continuous nanofibers. In the field of biomaterials, new materials include nanofibers made of chitosan. Numerous medications, including antibiotics, chemotherapeutic agents, proteins, and analgesics for inflammatory pain, have been successfully loaded onto electro-spun nanofibers, according to recent investigations. Chitosan nanofibers have several exceptional qualities that make them ideal for use in important pharmaceutical applications, such as tissue engineering, drug delivery systems, wound dressing, and enzyme immobilization. The preparation of chitosan nanofibers, followed by a discussion of the biocompatibility and degradation of chitosan nanofibers, followed by a description of how to load the drug into the nanofibers, are the first issues highlighted by this review of chitosan nanofibers in drug delivery applications. The main uses of chitosan nanofibers in drug delivery systems will be discussed last.

Fungicide exposure accelerated horizontal transfer of antibiotic resistance genes via plasmid-mediated conjugation

Co-pollution of soil with pesticide residues and antibiotic resistance genes (ARGs) is increasing due to the substantial usage of pesticides and organic fertilizers in greenhouse-based agricultural production. Non-antibiotic stresses, including those from agricultural fungicides, are potential co-selectors for the horizontal transfer of ARGs, but the underlying mechanism remains unclear. Intragenus and intergenus conjugative transfer systems of the antibiotic resistant plasmid RP4 were established to examine conjugative transfer frequency under stress from four widely used fungicides: triadimefon, chlorothalonil, azoxystrobin, and carbendazim. The mechanisms were elucidated at the cellular and molecular levels using transmission electron microscopy, flow cytometry, RT-qPCR, and RNA-seq techniques. The conjugative transfer frequency of plasmid RP4 between Escherichia coli strains increased with the rising exposure concentrations of chlorothalonil, azoxystrobin, and carbendazim, but was suppressed between E. coli and Pseudomonas putida by a high fungicide concentration (10 µg/mL). Triadimefon did not significantly affect conjugative transfer frequency. Exploration of the underlying mechanisms revealed that: (i) chlorothalonil exposure mainly promoted generation of intracellular reactive oxygen species, stimulated the SOS response, and increased cell membrane permeability, while (ii) azoxystrobin and carbendazim primarily enhanced expression of conjugation-related genes on the plasmid. These findings reveal the fungicide-triggered mechanisms associated with plasmid conjugation and highlight the potential role of non-bactericidal pesticides on the dissemination of ARGs.

A Genome-Wide Phenotypic Analysis of Saccharomyces cerevisiae’s Adaptive Response and Tolerance to Chitosan in Conditions Relevant for Winemaking

In the wine industry, the use of chitosan, a non-toxic biodegradable polysaccharide with antimicrobial properties, has been gaining interest with respect to envisaging the reduction in the use of sulfur dioxide (SO2). Although the mechanisms of toxicity of chitosan against fungal cells have been addressed before, most of the studies undertaken used other sources of chitosan and/or used conditions to solubilize the polymer that were not compatible with winemaking. Herein, the effect of a commercial formulation of chitosan approved for use in winemaking over the growth of the spoilage yeast species Dekkera anomala, Saccharomycodes ludwigii, Zygosaccharomyces bailii, and Pichia anomala was assessed. At the legally allowed concentration of 0.1 g/L, chitosan inhibited the growth of all spoilage yeasts, except for the tested Pichia anomala strains. Interestingly, the highly SO2-tolerant yeasts S. ludwigii and Z. bailii were highly susceptible to chitosan. The growth of commercial Saccharomyces cerevisiae was also impacted by chitosan, in a strain-dependent manner, albeit at higher concentrations. To dissect this differential inhibitory potential and gain further insight into the interaction of chitosan over fungal cells, we explored a chemogenomic analysis to identify all of the S. cerevisiae genes conferring protection against or increasing susceptibility to the commercial formulation of chitosan. Among the genes found to confer protection against chitosan, a high proportion was found to encode proteins required for the assembly and structuring of the cell wall, enzymes involved in the synthesis of plasma membrane lipids, and components of signaling pathways that respond to damages in the plasma membrane (e.g., the Rim101 pathway). The data obtained also suggest that the fungal ribosome and the vacuolar V-ATPase could be directly targeted by chitosan, since the deletion of genes encoding proteins required for the structure and function of these organelles was found to increase tolerance to chitosan. We also demonstrated, for the first time, that the deletion of ITR1, AGP2 and FPS1, encoding plasma membrane transporters, prominently increased the tolerance of S. cerevisiae to chitosan, suggesting that they can serve as carriers for chitosan. Besides providing new insights into the mode of action of chitosan against wine yeasts, this study adds relevant information for its rational use as a substitute/complementary preservative to SO2.

Elicitation of Fruit Fungi Infection and Its Protective Response to Improve the Postharvest Quality of Fruits

Fruit diseases brought on by fungus infestation leads to postharvest losses of fresh fruit. Approximately 30% of harvested fruits do not reach consumers’ plates due to postharvest losses. Fungal pathogens play a substantial part in those losses, as they cause the majority of fruit rots and consumer complaints. Understanding fungal pathogenic processes and control measures is crucial for developing disease prevention and treatment strategies. In this review, we covered the presented pathogen entry, environmental conditions for pathogenesis, fruit’s response to pathogen attack, molecular mechanisms by which fungi infect fruits in the postharvest phase, production of mycotoxin, virulence factors, fungal genes involved in pathogenesis, and recent strategies for protecting fruit from fungal attack. Then, in order to investigate new avenues for ensuring fruit production, existing fungal management strategies were then assessed based on their mechanisms for altering the infection process. The goal of this review is to bridge the knowledge gap between the mechanisms of fungal disease progression and numerous disease control strategies being developed for fruit farming.

Chitosan: An Autocidal Molecule of Plant Pathogenic Fungus

The rise in the world's food demand with the increasing population threatens the existence of civilization with two equally valuable concerns: increase in global food production and sustainability in the ecosystem. Furthermore, biotic and abiotic stresses are adversely affecting agricultural production. Among them, losses caused by insect pests and pathogens have been shown to be more destructive to agricultural production. However, for winning the battle against the abundance of insect pests and pathogens and their nature of resistance development, the team of researchers is searching for an alternative way to minimize losses caused by them. Chitosan, a natural biopolymer, coupled with a proper application method and effective dose could be an integral part of sustainable alternatives in the safer agricultural sector. In this review, we have integrated the insight knowledge of chitin-chitosan interaction, successful and efficient use of chitosan, recommended and practical methods of use with well-defined doses, and last but not least the dual but contrast mode of action of the chitosan in hosts and as well as in pathogens.

Mode of action of nanochitin whisker against Fusarium pseudograminearum

Nanochitin whisker (NC) is an advanced nanobiomaterial with novel physicochemical and biological properties. Fusarium pseudograminearum (Fpg) is an important pathogenic fungus causing wheat crown rot disease. This study explored the mode of action of NC against Fpg as a target microorganism. The effects of different treatments and concentrations of NC on the fungal growth and conidial germination were investigated by in vitro bioassay. The impacts of NC on cell structure integrity, membrane permeability, pathogenesis related key enzymes activity, and the mycotoxin production were examined by electron microscopy, fluorescence spectroscopy, IR spectroscopy, conductometry, and spectrophotometry, respectively. The results showed that NC significantly reduced hyphal growth, and the spore germination rate of Fpg declined by 33.0 % and 23.2 % when Fpg was treated with 30 and 300 μg/mL of NC, respectively. NC vigorously influenced structural stability of cell wall by destroying dextran structure, and strongly stimulated ergosterol production altering membrane integrity of the fungus. It reduced the activities of enzymes related to energy-supply like nicotinamide adenine dinucleotide oxidase and succinate dehydrogenase remarkably. The production of fungal mycotoxin deoxynivalenol was also decreased by NC. These findings provide an important basis for fully understanding the mechanism of nanobiomaterial in plant fungal disease control.

Synergistic Antimicrobial Activities of Chitosan Mixtures and Chitosan–Copper Combinations

Several recent studies revealed the significant contribution of intensive agriculture to global climate change and biodiversity decline. However, synthetic pesticides and fertilizers, which are among the main reasons for these negative effects, are required to achieve the high performance of elite crops needed to feed the growing world population. Modern agro-biologics, such as biopesticides, biostimulants, and biofertilizers are intended to replace or reduce the current agro-chemicals, but the former are often difficult to combine with the latter. Chitosans, produced from the fisheries’ byproduct chitin, are among the most promising agro-biologics, and copper fungicides are among the most widely used plant protectants in organic farming. However, the two active ingredients tend to form precipitates, hindering product development. Here, we show that partial hydrolysis of a chitosan polymer can yield a mixture of smaller polymers and oligomers that act synergistically in their antifungal activity. The low molecular weight (Mw) of this hydrolysate allows its combination with copper acetate, again leading to a synergistic effect. Combined, these synergies allow a 50% reduction in copper concentration, while maintaining the antifungal activity. This is potentially a significant step towards a more sustainable agriculture.

Chitosan resistance by the deletion of the putative high affinity glucose transporter in the yeast Ustilago maydis

Chitosan is a polycationic amino-sugar polymer soluble in acidic pH. As a potential antifungal, it has been tested against several fungi. Its main mode of action is the permeabilization of cell membrane by the interaction with specific membrane sites. Ustilago maydis, an attractive fungal model used in biochemical and biotechnology research, is highly sensitive to chitosan, with extensive membrane destruction that results in cell death. Using the Golden Gate system, several mutant strains with deletions in monosaccharide transporters were obtained and tested against chitosan in order to know the implications of these membrane proteins in the sensitivity of the fungus against chitosan. Δum11514/03895 strain, a mutant with a deletion in a hypothetical high affinity glucose transporter, showed resistance to chitosan. Morphological characterization of the mutant displayed an apparent increase in mitochondrial content, but oxygen consumption as well as growth rate were not affected by the gene deletion. Alteration in cell wall surface was observed in the mutant strain. In contrast to wild type, the Δum11514/03895 strain showed integrity of cell wall and cell membrane in the presence of chitosan. The resistance against chitosan is likely associated to the modification of cell wall architecture and is not related to energy-depend process.

Chitosan inhibits septin-mediated plant infection by the rice blast fungus Magnaporthe oryzae in a protein kinase C and Nox1 NADPH oxidase-dependent manner

Chitosan is a partially deacetylated linear polysaccharide composed of β-1,4-linked units of d-glucosamine and N-acetyl glucosamine. As well as a structural component of fungal cell walls, chitosan is a potent antifungal agent. However, the mode of action of chitosan is poorly understood. Here, we report that chitosan is effective for control of rice blast disease. Chitosan application impairs growth of the blast fungus Magnaporthe oryzae and has a pronounced effect on appressorium-mediated plant infection. Chitosan inhibits septin-mediated F-actin remodelling at the appressorium pore, thereby preventing repolarization of the infection cell. Chitosan causes plasma membrane permeabilization of M. oryzae and affects NADPH oxidase-dependent synthesis of reactive oxygen species, essential for septin ring formation and fungal pathogenicity. We further show that toxicity of chitosan to M. oryzae requires the protein kinase C-dependent cell wall integrity pathway, the Mps1 mitogen-activated protein kinase and the Nox1 NADPH oxidase. A conditionally lethal, analogue (PP1)-sensitive mutant of Pkc1 is partially remediated for growth in the presence of chitosan, while ∆nox1 mutants increase their glucan : chitin cell wall ratio, rendering them resistant to chitosan. Taken together, our data show that chitosan is a potent fungicide which requires the cell integrity pathway, disrupts plasma membrane function and inhibits septin-mediated plant infection.

Antimicrobial Actions and Applications of Chitosan

Chitosan is a naturally originating product that can be applied in many areas due to its biocompatibility, biodegradability, and nontoxic properties. The broad-spectrum antimicrobial activity of chitosan offers great commercial potential for this product. Nevertheless, the antimicrobial activity of chitosan varies, because this activity is associated with its physicochemical characteristics and depends on the type of microorganism. In this review article, the fundamental properties, modes of antimicrobial action, and antimicrobial effects-related factors of chitosan are discussed. We further summarize how microorganisms genetically respond to chitosan. Finally, applications of chitosan-based biomaterials, such as nanoparticles and films, in combination with current clinical antibiotics or antifungal drugs, are also addressed.

Chitosan modulates Pochonia chlamydosporia gene expression during nematode egg parasitism

Climate change makes plant‐parasitic nematodes (PPN) an increasing threat to commercial crops. PPN can be managed sustainably by the biocontrol fungus Pochonia chlamydosporia (Pc). Chitosan generated from chitin deacetylation enhances PPN parasitism by Pc. In this work, we investigate the molecular mechanisms of Pc for chitosan resistance and root‐knot nematode (RKN) parasitism, using transcriptomics. Chitosan and RKN modify the expression of Pc genes, mainly those involved in oxidation–reduction processes. Both agents significantly modify the expression of genes associated to 113 GO terms and 180 Pc genes. Genes encoding putative glycoproteins (Pc adhesives) to nematode eggshell, as well as genes involved in redox, carbohydrate and lipid metabolism trigger the response to chitosan. We identify genes expressed in both the parasitic and endophytic phases of the Pc lifecycle; these include proteases, chitosanases and transcription factors. Using the Pathogen—Host Interaction database (PHI‐base), our previous RNA‐seq data and RT‐PCR of Pc colonizing banana we have investigated genes expressed both in the parasitic and endophytic phases of Pc lifecycle.

Chitosan Induces Plant Hormones and Defenses in Tomato Root Exudates

In this work, we use electrophysiological and metabolomic tools to determine the role of chitosan as plant defense elicitor in soil for preventing or manage root pests and diseases sustainably. Root exudates include a wide variety of molecules that plants and root microbiota use to communicate in the rhizosphere. Tomato plants were treated with chitosan. Root exudates from tomato plants were analyzed at 3, 10, 20, and 30 days after planting (dap). We found, using high performance liquid chromatography (HPLC) and excitation emission matrix (EEM) fluorescence, that chitosan induces plant hormones, lipid signaling and defense compounds in tomato root exudates, including phenolics. High doses of chitosan induce membrane depolarization and affect membrane integrity. 1H-NMR showed the dynamic of exudation, detecting the largest number of signals in 20 dap root exudates. Root exudates from plants irrigated with chitosan inhibit ca. twofold growth kinetics of the tomato root parasitic fungus Fusarium oxysporum f. sp. radicis-lycopersici. and reduced ca. 1.5-fold egg hatching of the root-knot nematode Meloidogyne javanica.

+Brettanomyces bruxellensis Displays Variable Susceptibility to Chitosan Treatment in Wine

Brettanomyces bruxellensis is the main spoilage microbial agent in red wines. The use of fungal chitosan has been authorized since 2009 as a curative treatment to eliminate this yeast in conventional wines and in 2018 in organic wines. As this species is known to exhibit great genetic and phenotypic diversity, we examined whether all the strains responded the same way to chitosan treatment. A collection of 53 strains of B. bruxellensis was used. In the conditions of the reference test, all were at least temporarily affected by the addition of chitosan to wine, with significant decrease of cultivable population. Some (41%) were very sensitive and no cultivable yeast was detected in wine or lees after 3 days of treatment, while others (13%) were tolerant and, after a slight drop in cultivability, resumed growth between 3 and 10 days and remained able to produce spoilage compounds. There were also many strains with intermediate behavior. The strain behavior was only partially linked to the strain genetic group. This behavior was little modulated by the physiological state of the strain or the dose of chitosan used (within the limits of the authorized doses). On the other hand, for a given strain, the sensitivity to chitosan treatment was modulated by the chitosan used and by the properties of the wine in which the treatment was carried out.

The ADP-ribosylation factor-like small GTPase FgArl1 participates in growth, pathogenicity and DON production in Fusarium graminearum

Fusarium graminearum is the main pathogen of Fusarium head blight (FHB) in wheat and related species, which causes serious production decreases and economic losses and produces toxins such as deoxynivalenol (DON), which endangers the health of humans and livestock. Vesicle transport is a basic physiological process required for cell survival in eukaryotes. Many regulators of vesicle transport are reported to be involved in the pathogenicity of fungi. In yeast and mammalian cells, the ADP-ribosylation factor-like small GTPase Arl1 and its orthologs are involved in regulating vesicular trafficking, cytoskeletal reorganization and other significant biological processes. However, the role of Arl1 in F. graminearum is not well understood. In this study, we characterized the Arl1-homologous protein FgArl1 in F. graminearum and showed that FgArl1 is located in the trans-Golgi apparatus. The deletion of FgARL1 resulted in a significant decrease in vegetative growth and pathogenicity. Further analyses of the ΔFgarl1 mutant revealed defects in the production of DON. Taken together, these results indicate that FgArl1 is important in the development and pathogenicity of F. graminearum.

Advances in fungal chemical genomics for the discovery of new antifungal agents

Invasive fungal infections have escalated from a rare curiosity to a major cause of human mortality around the globe. This is in part due to a scarcity in the number of antifungal drugs available to combat mycotic disease, making the discovery of novel bioactive compounds and determining their mode of action of utmost importance. The development and application of chemical genomic assays using the model yeast Saccharomyces cerevisiae has provided powerful methods to identify the mechanism of action of diverse molecules in a living cell. Furthermore, complementary assays are continually being developed in fungal pathogens, most notably Candida albicans and Cryptococcus neoformans, to elucidate compound mechanism of action directly in the pathogen of interest. Collectively, the suite of chemical genetic assays that have been developed in multiple fungal species enables the identification of candidate drug target genes, as well as genes involved in buffering drug target pathways, and genes involved in general cellular responses to small molecules. In this review, we examine current yeast chemical genomic assays and highlight how such resources provide powerful tools that can be utilized to bolster the antifungal pipeline.

Antibiotic saving effect of combination therapy through synergistic interactions between well-characterized chito-oligosaccharides and commercial antifungals against medically relevant yeasts

Combination therapies can be a help to overcome resistance to current antifungals in humans. The combined activity of commercial antifungals and soluble and well-defined low molecular weight chitosan with average degrees of polymerization (DP_n) of 17–62 (abbreviated C17 –C62) and fraction of acetylation (F_A) of 0.15 against medically relevant yeast strains was studied. The minimal inhibitory concentration (MIC) of C32 varied greatly among strains, ranging from > 5000 μg mL^-1 (Candida albicans and C. glabrata) to < 4.9 (C. tropicalis). A synergistic effect was observed between C32 and the different antifungals tested for most of the strains. Testing of several CHOS preparations indicated that the highest synergistic effects are obtained for fractions with a DP_n in the 30–50 range. Pre-exposure to C32 enhanced the antifungal effect of fluconazole and amphotericin B. A concentration-dependent post-antifungal effect conserved even 24 h after C32 removal was observed. The combination of C32 and commercial antifungals together or as part of a sequential therapy opens new therapeutic perspectives for treating yeast infections in humans.

A review on the preparation of chitosan oligosaccharides and application to human health, animal husbandry and agricultural production

Chitosan oligosaccharides (COS) are the degraded products of chitin or chitosan prepared by chemical or enzymatic hydrolysis. As compared to chitosan, COS not only exhibit some specific physicochemical properties such as excellent water solubility, biodegradability and biocompatibility, but also have a variety of functionally biological activities including anti-inflammation, anti-bacteria, immunomodulation, neuroprotection and so on. This review aims to summarize the preparation and structural characterization methods of COS, and will discuss the application of COS or their derivatives to human health, animal husbandry and agricultural production. COS have been demonstrated to prevent the occurrence of human health-related diseases, enhance the resistance to diseases of livestock and poultry, and improve the growth and quality of crops in plant cultivation. Overall, COS have presented a broad developmental potential and application prospect in the healthy field that deserves further exploration.

Modification of Chitosan for the Generation of Functional Derivatives

Today, chitosan (CS) is probably considered as a biofunctional polysaccharide with the most notable growth and potential for applications in various fields. The progress in chitin chemistry and the need to replace additives and non-natural polymers with functional natural-based polymers have opened many new opportunities for CS and its derivatives. Thanks to the specific reactive groups of CS and easy chemical modifications, a wide range of physico-chemical and biological properties can be obtained from this ubiquitous polysaccharide that is composed of β-(1,4)-2-acetamido-2-deoxy-d-glucose repeating units. This review is presented to share insights into multiple native/modified CSs and chitooligosaccharides (COS) associated with their functional properties. An overview will be given on bioadhesive applications, antimicrobial activities, adsorption, and chelation in the wine industry, as well as developments in medical fields or biodegradability.

Molecular Mechanisms of Chitosan Interactions with Fungi and Plants

Chitosan is a versatile compound with multiple biotechnological applications. This polymer inhibits clinically important human fungal pathogens under the same carbon and nitrogen status as in blood. Chitosan permeabilises their high-fluidity plasma membrane and increases production of intracellular oxygen species (ROS). Conversely, chitosan is compatible with mammalian cell lines as well as with biocontrol fungi (BCF). BCF resistant to chitosan have low-fluidity membranes and high glucan/chitin ratios in their cell walls. Recent studies illustrate molecular and physiological basis of chitosan-root interactions. Chitosan induces auxin accumulation in Arabidopsis roots. This polymer causes overexpression of tryptophan-dependent auxin biosynthesis pathway. It also blocks auxin translocation in roots. Chitosan is a plant defense modulator. Endophytes and fungal pathogens evade plant immunity converting chitin into chitosan. LysM effectors shield chitin and protect fungal cell walls from plant chitinases. These enzymes together with fungal chitin deacetylases, chitosanases and effectors play determinant roles during fungal colonization of plants. This review describes chitosan mode of action (cell and gene targets) in fungi and plants. This knowledge will help to develop chitosan for agrobiotechnological and medical applications.

Ethanol production from chitosan by the nematophagous fungus Pochonia chlamydosporia and the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana

Chitin is the second most abundant biopolymer after cellulose and virtually unexplored as raw material for bioethanol production. In this paper, we investigate chitosan, the deacetylated form of chitin which is the main component of shellfish waste, as substrate for bioethanol production by fungi. Fungal parasites of invertebrates such as the nematophagous Pochonia chlamydosporia (Pc) or the entomopathogens Beauveria bassiana (Bb) and Metarhizium anisopliae (Ma) are biocontrol agents of plant parasitic nematodes (eg. Meloidogyne spp.) or insect pests such as the red palm weevil (Rhynchophorus ferrugineus). These fungi degrade chitin-rich barriers for host penetration. We have therefore tested the chitin/chitosanolytic capabilities of Pc, Bb and Ma for generating reducing sugars using chitosan as only nutrient. Among the microorganisms used in this study, Pc is the best chitosan degrader, even under anaerobic conditions. These fungi have alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) encoding genes in their genomes. We have therefore analyzed their ethanol production under anaerobic conditions using chitosan as raw material. P. chlamydosporia is the largest ethanol producer from chitosan. Our studies are a starting point to develop chitin-chitosan based biofuels.

Multiple activities of Arl1 GTPase in the trans-Golgi network

ADP-ribosylation factors (Arfs) and ADP-ribosylation factor-like proteins (Arls) are highly conserved small GTPases that function as main regulators of vesicular trafficking and cytoskeletal reorganization. Arl1, the first identified member of the large Arl family, is an important regulator of Golgi complex structure and function in organisms ranging from yeast to mammals. Together with its effectors, Arl1 has been shown to be involved in several cellular processes, including endosomal trans-Golgi network and secretory trafficking, lipid droplet and salivary granule formation, innate immunity and neuronal development, stress tolerance, as well as the response of the unfolded protein. In this Commentary, we provide a comprehensive summary of the Arl1-dependent cellular functions and a detailed characterization of several Arl1 effectors. We propose that involvement of Arl1 in these diverse cellular functions reflects the fact that Arl1 is activated at several late-Golgi sites, corresponding to specific molecular complexes that respond to and integrate multiple signals. We also provide insight into how the GTP-GDP cycle of Arl1 is regulated, and highlight a newly discovered mechanism that controls the sophisticated regulation of Arl1 activity at the Golgi complex.

Signaling pathways coordinating the alkaline pH response confer resistance to the hevein-type plant antimicrobial peptide Pn-AMP1 in Saccharomyces cerevisiae

Genome-wide screening of Saccharomyces cerevisiae revealed that signaling pathways related to the alkaline pH stress contribute to resistance to plant antimicrobial peptide, Pn-AMP1. Plant antimicrobial peptides (AMPs) are considered to be promising candidates for controlling phytopathogens. Pn-AMP1 is a hevein-type plant AMP that shows potent and broad-spectrum antifungal activity. Genome-wide chemogenomic screening was performed using heterozygous and homozygous diploid deletion pools of Saccharomyces cerevisiae as a chemogenetic model system to identify genes whose deletion conferred enhanced sensitivity to Pn-AMP1. This assay identified 44 deletion strains with fitness defects in the presence of Pn-AMP1. Strong fitness defects were observed in strains with deletions of genes encoding components of several pathways and complex known to participate in the adaptive response to alkaline pH stress, including the cell wall integrity (CWI), calcineurin/Crz1, Rim101, SNF1 pathways and endosomal sorting complex required for transport (ESCRT complex). Gene ontology (GO) enrichment analysis of these genes revealed that the most highly overrepresented GO term was "cellular response to alkaline pH". We found that 32 of the 44 deletion strains tested (72 %) showed significant growth defects compared with their wild type at alkaline pH. Furthermore, 9 deletion strains (20 %) exhibited enhanced sensitivity to Pn-AMP1 at ambient pH compared to acidic pH. Although several hundred plant AMPs have been reported, their modes of action remain largely uncharacterized. This study demonstrates that the signaling pathways that coordinate the adaptive response to alkaline pH also confer resistance to a hevein-type plant AMP in S. cerevisiae. Our findings have broad implications for the design of novel and potent antifungal agents.

Tolerance to chitosan by Trichoderma species is associated with low membrane fluidity

The effect of chitosan on growth of Trichoderma spp., a cosmopolitan genus widely exploited for their biocontrol properties was evaluated. Based on genotypic (ITS of 18S rDNA) characters, four isolates of Trichoderma were identified as T. pseudokoningii FLM16, T. citrinoviride FLM17, T. harzianum EZG47, and T. koningiopsis VSL185. Chitosan reduces radial growth of Trichoderma isolates in concentration-wise manner. T. koningiopsis VSL185 was the most chitosan tolerant isolate in all culture media amended with chitosan (0.5-2.0 mg ml(-1) ). Minimal Inhibitory Concentration (MIC) and Minimal Fungicidal Concentration (MFC) were determined showing that T. koningiopsis VSL185 displays higher chitosan tolerance with MIC value >2000 μg ml(-1) while for other Trichoderma isolates MIC values were around 10 μg ml(-1) . Finally, free fatty acid composition reveals that T. koningiopsis VSL185, chitosan tolerant isolate, displays lower linolenic acid (C18:3) content than chitosan sensitive Trichoderma isolates. Our findings suggest that low membrane fluidity is associated with chitosan tolerance in Trichoderma spp.

Lichen-forming fungus Caloplaca flavoruscens inhibits transcription factors and chromatin remodeling system in fungi

Lichen-forming fungi and extracts derived from them have been used as alternative medicine sources for millennia and recently there has been a renewed interest in their known bioactive properties for anticancer agents, cosmetics and antibiotics. Although lichen-forming fungus-derived compounds are biologically and commercially valuable, few studies have been performed to determine their modes of action. This study used chemical-genetic and chemogenomic high-throughput analyses to gain insight into the modes of action of Caloplaca flavoruscens extracts. High-throughput screening of 575 lichen extracts was performed and 39 extracts were identified which inhibited yeast growth. A C. flavoruscens extract was selected as a promising antifungal and was subjected to genome-wide haploinsufficiency profiling and homozygous profiling assays. These screens revealed that yeast deletion strains lacking Rsc8, Pro1 and Toa2 were sensitive to three concentrations (IC25.5, IC25 and IC50, respectively) of C. flavoruscens extract. Gene-enrichment analysis of the data showed that C. flavoruscens extracts appear to perturb transcription and chromatin remodeling.

Omics for Investigating Chitosan as an Antifungal and Gene Modulator

Chitosan is a biopolymer with a wide range of applications. The use of chitosan in clinical medicine to control infections by fungal pathogens such as Candida spp. is one of its most promising applications in view of the reduced number of antifungals available. Chitosan increases intracellular oxidative stress, then permeabilizes the plasma membrane of sensitive filamentous fungus Neurospora crassa and yeast. Transcriptomics reveals plasma membrane homeostasis and oxidative metabolism genes as key players in the response of fungi to chitosan. A lipase and a monosaccharide transporter, both inner plasma membrane proteins, and a glutathione transferase are main chitosan targets in N. crassa. Biocontrol fungi such as Pochonia chlamydosporia have a low content of polyunsaturated free fatty acids in their plasma membranes and are resistant to chitosan. Genome sequencing of P. chlamydosporia reveals a wide gene machinery to degrade and assimilate chitosan. Chitosan increases P. chlamydosporia sporulation and enhances parasitism of plant parasitic nematodes by the fungus. Omics studies allow understanding the mode of action of chitosan and help its development as an antifungal and gene modulator.

Newer patents in antimycotic therapy

There has been a global upsurge in fungal infections due to rise in immunodeficiencies, debilitation and situations of violated anatomical barriers. The available antifungal repertoire has limited activity and is fraught with toxicity concerns. Drug resistance has also shown a rapid upward trend. This has resulted in increased treatment failures, mortality and health care costs. Novel effective and safe antimycotics are needed. Analogues of existing antifungal compounds and new molecules are being developed. New targets are being explored for their putative role in curtailing fungal infections. Newer antigens as vaccine candidates are being researched into. Focused efforts in this direction have yielded encouraging results. This review illuminates the various antifungal strategies which hold promise for the future.

Neurospora crassa transcriptomics reveals oxidative stress and plasma membrane homeostasis biology genes as key targets in response to chitosan

Chitosan is a natural polymer with antimicrobial activity. Chitosan causes plasma membrane permeabilization and induction of intracellular reactive oxygen species (ROS) in Neurospora crassa. We have determined the transcriptional profile of N. crassa to chitosan and identified the main gene targets involved in the cellular response to this compound. Global network analyses showed membrane, transport and oxidoreductase activity as key nodes affected by chitosan. Activation of oxidative metabolism indicates the importance of ROS and cell energy together with plasma membrane homeostasis in N. crassa response to chitosan. Deletion strain analysis of chitosan susceptibility pointed NCU03639 encoding a class 3 lipase, involved in plasma membrane repair by lipid replacement, and NCU04537 a MFS monosaccharide transporter related to assimilation of simple sugars, as main gene targets of chitosan. NCU10521, a glutathione S-transferase-4 involved in the generation of reducing power for scavenging intracellular ROS is also a determinant chitosan gene target. Ca(2+) increased tolerance to chitosan in N. crassa. Growth of NCU10610 (fig 1 domain) and SYT1 (a synaptotagmin) deletion strains was significantly increased by Ca(2+) in the presence of chitosan. Both genes play a determinant role in N. crassa membrane homeostasis. Our results are of paramount importance for developing chitosan as an antifungal.

Comparison of the Antimicrobial Properties of Chitosan Oligosaccharides (COS) and EDTA against Fusarium fujikuroi Causing Rice Bakanae Disease

Bakanae disease is a destructive rice disease in South Korea caused by Fusarium fujikuroi infection. Chemical fungicides have been used to manage the disease, but the emergence of fungicide-resistant strains has gradually increased. Two chelating agents, chitosan oligosaccharides (COS) and ethylenediaminetetraacetatic acid (EDTA), are well known as biosafe and biocompatible antimicrobial agents. In this study, we compared the actions of COS and EDTA to gain a better understanding of the underlying antimicrobial activities and to evaluate them as eco-friendly fungicides against F. fujikuroi. While COS exhibited a rapid fungicidal effect on hyphal growing cells within 5 min, EDTA had a fungistatic effect on reversible growth inhibition. Scanning electron microscopy revealed that COS treatment resulted in pore-formation and cellular leakage along the growing hyphae, whereas EDTA caused no significant morphological changes. COS activity was greatly suppressed by the addition of Ca(2+) to the medium, and EDTA action was largely suppressed by Mn(2+) and slightly by Ca(2+), respectively. Taken together, these results indicated that two chelating agents, COS and EDTA, have different modes of antimicrobial action on F. fujikuroi. Thus, the combination of chelating agents having different modes of action might be an effective disease management strategy to prevent or delay the development of fungicide-resistant strains.

Evolutionary analysis of multidrug resistance genes in fungi - impact of gene duplication and family conservation

Although the emergence of bacterial drug resistance is of great concern to the scientific community, few studies have evaluated this phenomenon systematically in fungi by using genome-wide datasets. In the present study, we assembled a large compendium of Saccharomyces cerevisiae chemical genetic data to study the evolution of multidrug resistance genes (MDRs) in the fungal lineage. We found that MDRs typically emerge in widely conserved families, most of which containing homologs from pathogenic fungi, such as Candida albicans and Coccidioides immitis, which could favor the evolution of drug resistance in those species. By integrating data from chemical genetics with protein family conservation, genetic and protein interactions, we found that gene families rarely have more than one MDR, indicating that paralogs evolve asymmetrically with regard to multidrug resistance roles. Furthermore, MDRs have more genetic and protein interaction partners than non-MDRs, supporting their participation in complex biochemical systems underlying the tolerance to multiple bioactive molecules. MDRs share more chemical genetic interactions with other MDRs than with non-MDRs, regardless of their evolutionary affinity. These results suggest the existence of an intricate system involved in the global drug tolerance phenotypes. Finally, MDRs are more likely to be hit repeatedly by mutations in laboratory evolution experiments, indicating that they have great adaptive potential. The results presented here not only reveal the main genomic features underlying the evolution of MDRs, but also shed light on the gene families from which drug resistance is more likely to emerge in fungi.