Showing papers on "Chitin published in 2008"

A LysM Receptor-Like Kinase Plays a Critical Role in Chitin Signaling and Fungal Resistance in Arabidopsis

Abstract: Chitin, a polymer of N -acetyl-d-glucosamine, is found in fungal cell walls but not in plants. Plant cells can perceive chitin fragments (chitooligosaccharides) leading to gene induction and defense responses. We identified a LysM receptor-like protein (LysM RLK1) required for chitin signaling in Arabidopsis thaliana . The mutation in this gene blocked the induction of almost all chitooligosaccharide-responsive genes and led to more susceptibility to fungal pathogens but had no effect on infection by a bacterial pathogen. Additionally, exogenously applied chitooligosaccharides enhanced resistance against both fungal and bacterial pathogens in the wild-type plants but not in the mutant. Together, our data indicate that LysM RLK1 is essential for chitin signaling in plants (likely as part of the receptor complex) and is involved in chitin-mediated plant innate immunity. The LysM RLK1-mediated chitin signaling pathway is unique, but it may share a conserved downstream pathway with the FLS2/flagellin- and EFR/EF-Tu–mediated signaling pathways. Additionally, our work suggests a possible evolutionary relationship between the chitin and Nod factor perception mechanisms due to the similarities between their potential receptors and between the signal molecules perceived by them.

Stimulation of chitin synthesis rescues Candida albicans from echinocandins.

Abstract: Echinocandins are a new generation of novel antifungal agent that inhibit cell wall β(1,3)-glucan synthesis and are normally cidal for the human pathogen Candida albicans. Treatment of C. albicans with low levels of echinocandins stimulated chitin synthase (CHS) gene expression, increased Chs activity, elevated chitin content and reduced efficacy of these drugs. Elevation of chitin synthesis was mediated via the PKC, HOG, and Ca2+-calcineurin signalling pathways. Stimulation of Chs2p and Chs8p by activators of these pathways enabled cells to survive otherwise lethal concentrations of echinocandins, even in the absence of Chs3p and the normally essential Chs1p, which synthesize the chitinous septal ring and primary septum of the fungus. Under such conditions, a novel proximally offset septum was synthesized that restored the capacity for cell division, sustained the viability of the cell, and abrogated morphological and growth defects associated with echinocandin treatment and the chs mutations. These findings anticipate potential resistance mechanisms to echinocandins. However, echinocandins and chitin synthase inhibitors synergized strongly, highlighting the potential for combination therapies with greatly enhanced cidal activity.

TLR-2 and IL-17A in chitin-induced macrophage activation and acute inflammation.

Abstract: Chitin is a ubiquitous polysaccharide in fungi, insects, and parasites. To test the hypothesis that chitin is an important immune modulator, we characterized the ability of chitin fragments to regulate murine macrophage cytokine production in vitro and induce acute inflammation in vivo. In this study, we show that chitin is a size-dependent stimulator of macrophage IL-17A production and IL-17AR expression and demonstrate that these responses are TLR-2 and MyD88-dependent. We further demonstrate that IL-17A pathway activation is an essential event in the stimulation of some but not all chitin-stimulated cytokines and that chitin uses a TLR-2, MyD88-, and IL-17A-dependent mechanism(s) to induce acute inflammation. These studies demonstrate that chitin is a size-dependent pathogen-associated molecular pattern that activates TLR-2 and MyD88 in a novel IL-17A/IL-17AR-based innate immunity pathway.

Conservation of the Chitin Utilization Pathway in the Vibrionaceae

Abstract: Vibrionaceae are regarded as important marine chitin degraders, and attachment to chitin regulates important biological functions; yet, the degree of chitin pathway conservation in Vibrionaceae is unknown. Here, a core chitin degradation pathway is proposed based on comparison of 19 Vibrio and Photobacterium genomes with a detailed metabolic map assembled for V. cholerae from published biochemical, genomic, and transcriptomic results. Further, to assess whether chitin degradation is a conserved property of Vibrionaceae, a set of 54 strains from 32 taxa were tested for the ability to grow on various forms of chitin. All strains grew on N-acetylglucosamine (GlcNAc), the monomer of chitin. The majority of isolates grew on α (crab shell) and β (squid pen) chitin and contained chitinase A (chiA) genes. chiA sequencing and phylogenetic analysis suggest that this gene is a good indicator of chitin metabolism but appears subject to horizontal gene transfer and duplication. Overall, chitin metabolism appears to be a core function of Vibrionaceae, but individual pathway components exhibit dynamic evolutionary histories.

Characterization of Chitin and Chitosan Molecular Structure in Aqueous Solution.

Abstract: Molecular dynamics simulations have been used to characterize the structure of single chitin and chitosan chains in aqueous solutions Chitin chains, whether isolated or in the form of a β-chitin nanoparticle, adopt the 2-fold helix with ϕ and φ values similar to its crystalline state In solution, the intramolecular hydrogen bond HO3(n)···O5(n+1) responsible for the 2-fold helical motif in these polysaccharides is stabilized by hydrogen bonds with water molecules in a well-defined orientation On the other hand, chitosan can adopt five distinct helical motifs, and its conformational equilibrium is highly dependent on pH The hydrogen bond pattern and solvation around the O3 atom of insoluble chitosan (basic pH) are nearly identical to these quantities in chitin Our findings suggest that the solubility and conformation of these polysaccharides are related to the stability of the intrachain HO3(n)···O5(n+1) hydrogen bond, which is affected by the water exchange around the O3-HO3 hydroxyl group

Chitin purification from shrimp wastes by microbial deproteination and decalcification

Abstract: Chitin was purified from Penaeus monodon and Crangon crangon shells using a two-stage fermentation process with anaerobic deproteination followed by decalcification through homofermentative lactic acid fermentation. Deproteinating enrichment cultures from sewage sludge and ground meat (GM) were used with a proteolytic activity of 59 and 61 mg N l−1 h−1 with dried and 26 and 35 mg N l−1 h−1 with wet P. monodon shells. With 100 g wet cells of proteolytic bacteria per liter, protein removal was obtained in 42 h. An anaerobic spore-forming bacterium HP1 was isolated from enrichment GM. Its proteolytic activity was 76 U ml−1 compared to 44 U ml−1 of the consortium. Glucose was fermented with Lactobacillus casei MRS1 to lactic acid. At a pH of 3.6, calcium carbonate of the shells was solubilised. After deproteination and decalcification of P. monodon or C. crangon shells, the protein content was 5.8% or 6.7%, and the calcium content was 0.3% or 0.4%, respectively. The viscosity of the chitin from P. monodon and C. crangon was 45 and 135 mPa s, respectively, whereas purchased crab shell chitin (practical grade) had a viscosity of 21 mPa s, indicating a higher quality of biologically purified chitin.

Early events induced by chitosan on plant cells

Abstract: Chitosan (a polymer of beta-1,4-glucosamine residues) is a deacetylated derivative of chitin which presents antifungal properties and acts as a potent elicitor of plant resistance against fungal pathogens. Attention was focused in this study on the chitosan-induced early events in the elicitation chain. Thus, it was shown that chitosan triggered in a dose-dependent manner rapid membrane transient depolarization of Mimosa pudica motor cells and, correlatively, a transient rise of pH in the incubation medium of pulvinar tissues. By using plasma membrane vesicles (PMVs), it was specified that a primary site of action of the compound is the plasma membrane H(+)-ATPase as shown by its inhibitory effect on the proton pumping and the catalytic activity of the enzyme up to 250 microg ml(-1). As a consequence, chitosan treatment modified H(+)-mediated processes, in particular it inhibited the uptake of the H(+)-substrate co-transported sucrose and valine, and inhibited the light-induced H(+)/K(+)-mediated turgor reaction of motor cells. The present data also allowed the limit of the cytotoxicity of the compound to be established close to a concentration of 100 microg ml(-1) at the plasma membrane level. As a consequence, chitosan could be preferably used in plant disease control as a powerful elicitor rather than a direct antifungal agent.

Evidence for the mechanism of action of the antifungal phytolaccoside B isolated from Phytolacca tetramera Hauman.

Abstract: Phytolaccoside B (1), an antifungal monodesmoside triterpenoid glycoside isolated from berries of Phytolacca tetramera Hauman (Phytolaccaceae), alters the morphology of yeasts and molds. The malformations were similar to those produced by enfumafungin, a known inhibitor of (1-->3)-beta-D-glucan synthase, an enzyme that catalyzes the synthesis of (1-->3)-beta-D-glucan, one of the major polymers of the fungal cell wall. However, enzymatic assays revealed that 1 did not inhibit (1-->3)-beta-D-glucan synthase, but it did produce a notable enhancement of the chitin synthase 1 activity and, concomitantly, a rise in chitin, another important polymer of the fungal cell walls. This finding was corroborated by fluorescence microscopy and also by quantification of the chitin. In addition, a 2-fold increase in the thickness of the fungal cell wall was observed with transmission electronic microscopy. On the other hand, 1 neither bound to ergosterol nor caused hemolysis of red blood cells, although some fungal membrane damage was observed at the MIC of 1.

Chitin signaling and plant disease resistance.

Abstract: Chitin, a polymer of N-acetyl-D-glucosamine, is a component of the fungal cell wall and is not found in plants. Plant cells are equipped with chitin degrading enzymes to digest fungal cell walls and are capable of perceiving chitin fragments (chitooligosaccharides) released from fungal cell walls during fungal infection. Chitin recognition results in the activation of defense signaling pathways. Although chitin is a well recognized pathogen-associated molecular pattern (PAMP), little is known about the molecular mechanism of chitin signaling. Recent studies identified a number of critical components in the chitin-elicited signaling pathway including a potential receptor, MAPK cascade and transcription factor network. Interestingly, the chitin signaling pathway overlaps with the phytobacterial flagellin-and EF-Tu-elicited signaling pathways, suggesting that plant cells may perceive different PAMPs from various pathogens via specialized receptors and then utilize a conserved, common downstream pathway to mediate disease resistance. Given the fact that fungal pathogens are major problems in many agricultural systems, research on chitin signaling could have significance to sustainable agriculture and biofuel and biomaterial production.

Chitin and Chitosan: Major Sources, Properties and Applications

Abstract: Chitin is widely distributed in nature, constituting an important renewable resource. The main sources of chitin generally used are the crustacean wastes of the fishing industry. This chapter provides a brief account of the main processes employed in chitin isolation and the preparation of chitosan by extensive deacetylation of chitin. The common methods of characterization of chitin and chitosan, in terms of degree of acetylation and molecular weight, are discussed. Their crystalline structure and their solution properties, are also described. The capacity of chitin and chitosan of forming complexes with metal ions is shown, and mention is made to some of its diverse applications. The ability of chitosan to form polyelectrolyte complexes with polyanions, the cooperativity of this reaction and the properties of chitosan-based polyelectrolyte complex membranes, are also examined. The chapter ends with a review of the applications of chitin and chitosan in medicine, pharmacy, agriculture, the food industry, cosmetics, among others. © 2008 Elsevier Ltd. All rights reserved.

Recovery of chitin and chitosan from shrimp waste by chemical and microbial methods

Abstract: Shrimp waste is the most important chitin source for commercial use. In this study chitin and chitosan were extracted from Penaeus semisulcatus waste collected from a shrimp processing landing center situated at Persian Gulf in south of Iran by chemical and microbial methods. Chitin and chitosan were extracted by alkali-acid treatment and the yields were 510 and 410mg/g, respectively. Demineralization is an important step in the chitin purification process from shrimp waste. Chemical extraction method included the use of NaOH solution and acetic acid. In microbial extraction, organic acids (lactic acid) produced by probiotic bacteria was used to demineralize microbial deproteinized shrimp shells. The study showed that the effectiveness of using lactic acid bacteria especially added Fe (NO3)3 as extra nitrogen source for demineralization of shrimp shells than chemical method (1750 against 810mg/g). Chitin and chitosan extracted from shrimp waste by chemical and microbial methods was crystalline powder, nonharmful and odorless, white and off-white, respectively. The moisture content was calculated as 63.8%. The amount of Ca, Fe, Cu and Mn present in the shells was 168, 35.58, 38.28 and 6.72mg/L, obtained by atomic absorption spectroscopy, respectively. The amount of calcium in the shells was 25 times higher than manganese. The results suggested Lactobacillus plantarum (PTTC 1058) is an attractive source of recovery for chitin and chitosan.

Mining marine shellfish wastes for bioactive molecules: Chitin and chitosan ndash; Part A: extraction methods

Abstract: Legal restrictions, high costs and environmental problems regarding the disposal of marine processing wastes have led to amplified interest in biotechnology research concerning the identification and extraction of additional high grade, low-volume by-products produced from shellfish waste treatments. Shellfish waste consisting of crustacean exoskeletons is currently the main source of biomass for chitin production. Chitin is a polysaccharide composed of N-acetyl-D-glucosamine units and the multidimensional utilization of chitin derivatives including chitosan, a deacetylated derivative of chitin, is due to a number of characteristics including: their polyelectrolyte and cationic nature, the presence of reactive groups, high adsorption capacities, bacteriostatic and fungistatic influences, making them very versatile biomolecules. Part A of this review aims to consolidate useful information concerning the methods used to extract and characterize chitin, chitosan and glucosamine obtained through industrial, microbial and enzymatic hydrolysis of shellfish waste.

Chapter 2 Enzymes of saprotrophic basidiomycetes

Abstract: Decomposer fungi utilize dead organic matter that is mainly composed of cell wall polysaccharides and other biopolymers. These include cell wall polymers of plant origin (cellulose, hemicelluloses, lignin, pectin), cell wall polysaccharides of fungi (chitin) and nutrient reserve polysaccharide (starch) as well as proteins. Utilization of these polymers necessitates production of extracellular enzymes; the polysaccharide-based biopolymers are usually degraded by hydrolytic enzymes causing endo and/or exocleavage. Lyases and specific oxidases are also produced. Wood-rotting cellulolytic fungi have evolved complex systems of nonenzymatic cellulose cleavage based on the production of reactive oxygen species, but the detailed functioning and relative importance of this decomposition mechanism is still unclear. Lignin decomposition is catalyzed by a set of oxidases and peroxidases with auxiliary enzymes providing hydroxyl radicals, but it also include the provision of enzyme cosubstrates such as organic acids or aryl alcohols. The composition of ligninolytic systems is thus very complex and species-specific. Compared to decomposition of wood, far less is known about basidiomycete species decomposing litter. Some litter-decomposing fungi are apparently physiologically related to ligninolytic wood-rotters but the compositions and regulation of their ligninolytic systems is not so well characterized, and little is known of their enzymology in the natural soil environment. However, it seems clear that litter decomposers are able to degrade lignin as well as cellulose and hemicelluloses and probably also chitin and starch. Their ligninolytic system also plays an important role in the transformation of humic substances including humus formation and mineralization. The main gaps in our current knowledge are in the ecology of enzyme production under natural conditions and in estimating the role of decomposer basidiomycetes in complex biological processes in soils.

Determination of glucosamine and N-acetyl glucosamine in fungal cell walls.

Abstract: A new method was developed to determine glucosamine (GlcN) and N-acetyl glucosamine (GlcNAc) in materials containing chitin and chitosan, such as fungal cell walls. It is based on two steps of hydrolysis with (i) concentrated sulfuric acid at low temperature and (ii) dilute sulfuric acid at high temperature, followed by one-step degradation with nitrous acid. In this process, chitin and chitosan are converted into anhydromannose and acetic acid. Anhydromannose represents the sum of GlcN and GlcNAc, whereas acetic acid is a marker for GlcNAc only. The method showed recovery of 90.1% of chitin and 85.7-92.4% of chitosan from commercial preparations. Furthermore, alkali insoluble material (AIM) from biomass of three strains of zygomycetes, Rhizopus oryzae, Mucor indicus, and Rhizomucor pusillus, was analyzed by this method. The glucosamine contents of AIM from R. oryzae and M. indicus were almost constant (41.7 +/- 2.2% and 42.0 +/- 1.7%, respectively), while in R. pusillus, it decreased from 40.0 to 30.0% during cultivation from 1 to 6 days. The GlcNAc content of AIM from R. oryzae and R. pusillus increased from 24.9 to 31.0% and from 36.3 to 50.8%, respectively, in 6 days, while it remained almost constant during the cultivation of M. indicus (23.5 +/- 0.8%).