Cell Wall Rigidity Research Articles

Morphological and proteomic analysis of early stage air-liquid interface biofilm formation in Mycobacterium smegmatis.

We studied the early stages of pellicle formation by Mycobacterium smegmatis on the surface of a liquid medium [air-liquid interface (A-L)]. Using optical and scanning electron microscopy, we showed the formation of a compact biofilm pellicle from micro-colonies over a period of 8-30 h. The cells in the pellicle changed size and cell division pattern during this period. Based on our findings, we created a model of M. smegmatis A-L early pellicle formation showing the coordinate growth of cells in the micro-colonies and in the homogeneous film between them, where the accessibility to oxygen and nutrients is different. A proteomic approach utilizing high-resolution two-dimensional gel electrophoresis, in combination with mass spectrometry-based protein identification, was used to analyse the protein expression profiles of the different morphological stages of the pellicle. The proteins identified formed four expression groups; the most interesting of these groups contained the proteins with highest expression in the biofilm development phase, when the floating micro-colonies containing long and more robust cells associate into flocs and start to form a compact pellicle. The majority of these proteins, including GroEL1, are involved in cell wall synthesis or modification, mostly through the involvement of mycolic acid biosynthesis, and their expression maxima correlated with the changes in cell size and the rigidity of the bacterial cell wall observed by scanning electron microscopy.

Variation in the Degree of Pectin Methylesterification during the Development of Baccharis dracunculifolia Kidney-Shaped Gall

Insect galls may be study models to test the distribution of pectins and arabinogalactan-proteins (AGPs) and their related functions during plant cell cycles. These molecules are herein histochemically and immunocitochemically investigated in the kidney-shaped gall induced by Baccharopelma dracunculifoliae (Psyllidae) on leaves of Baccharis dracunculifolia DC. (Asteraceae) on developmental basis. The homogalacturonans (HGAs) (labeled by JIM5) and the arabinans (labeled by LM6) were detected either in non-galled leaves or in young galls, and indicated stiffening of epidermal cell walls, which is an important step for cell redifferentiation. The labeling of HGAs by JIM7 changed from young to senescent stage, with an increase in the rigidity of cell walls, which is important for the acquaintance of the final gall shape and for the mechanical opening of the gall. The variation on the degree of HGAs during gall development indicated differential PMEs activity during gall development. The epitopes recognized by LM2 (AGP glycan) and LM5 (1–4-β-D-galactans) had poor alterations from non-galled leaves towards gall maturation and senescence. Moreover, the dynamics of pectin and AGPs on two comparable mature kidney-shaped galls on B. dracunculifolia and on B. reticularia revealed specific peculiarities. Our results indicate that similar gall morphotypes in cogeneric host species may present distinct cell responses in the subcelular level, and also corroborate the functions proposed in literature for HGAs.

Effects of NaCl on Root Growth and Cell Wall Composition of Two Soya bean Cultivars with Contrasting Salt Tolerance

AbstractOur objectives were to determine the influence of salinity on root cell wall composition in soya beans and the possible mechanism of salt tolerance. Two soya bean cultivars, Touzan 69 (salt sensitive) and Dare (salt tolerant), were selected as experimental material for comparison. Root growth was clearly inhibited by salinity in both cultivars, but Touzan 69 showed more severe reductions in root length than Dare. In the 0–5 mm root segment (from root tip), the total cell wall sugar content of Touzan 69 decreased considerably due to salinity as were the pectin, hemicellulose and cellulose fractions. In Dare, NaCl treatments only caused a slight decrease in the pectin fraction and no marked change in hemicellulose and cellulose fractions. Without salt treatment, the pectin fraction accounted for about 40 % and cellulose for 30 % of cell wall composition in the 0–5 mm root segment; in the 5–10 segment (from root tip), pectin and cellulose accounted for 27 % and 45 % in Touzan 69, and 34 % and 38 % in Dare. The percentage of pectin decreased and that of cellulose increased in the 5–10 mm root segment compared with the 0–5 mm segment. This indicates that pectin largely regulates cell growth, as the 0–5 mm region is considered the elongation zone of soya bean roots. Salt treatment decreased the percentage of pectin, but increased that of cellulose across root zones of the two cultivars, suggesting that salt presence may increase cell wall rigidity, and thus, inhibits root growth. Dare was able to maintain its main root cell wall substances, an apparent advantage for root cell growth that may overall improve its salt tolerance. Also, the less reduction in cell wall uronic acid was of some benefit in the positive regulation of root cell growth in Dare. The changes in cell wall composition, especially the pectin content had a close relation with the regulation of root growth. The difference in salt tolerance between the two tested cultivars can partly be explained on the basis of these changes in response to salinity. Sugar compounds in each cell wall constituent and their functions in ion transport as well as the relationship between root cell wall and soya bean salt tolerance need to be further investigated.

Risk assessment of wetland under aluminium and iron toxicities: A review

The chemical composition of aquatic habitat, environmental conditions and trend monitoring could reflect changes in species composition over time. Vegetation plays an important role in decontamination and waste treatment water inlet and received by wetlands. They provide carbon substrate for microbes which are important in processing wastewater contaminants. Metabolism in plants, however, requires micronutrients such as Aluminium (Al) and Iron (Fe). Al is toxic to many plants at concentrations greater than 2–3 pap at soil pH < 5.5. Al interferes with cell divisions in root tips and lateral roots, increases cell wall rigidity, maintains proper cellular redox state and various other biochemical, physiological and growth responses. Excess concentration of reducible Fe on acidic soils poses constraint primarily on wetland plants. The authors evaluate aspects of Al and Fe in anoxic biochemical processes, Al and Fe uptake, transport and distribution in wetland ecosystem. The review objective is to focus on wetland monitoring, as it was discovered that wetland ecosystems are at risk of degradation unless properly managed. A poor understanding of the value of wetlands will continue to encourage resource overuse and degradation, thus escalating threats to development through the environmental risk associated with remobilization of metal contaminants and the recycling to the food chain. Protection and restoration of aquatic ecosystems and their services in the face of pressures from land-use change, urbanization, and global warming which affects climate change, rising sea level, coastal erosion and lowland flooding are important.

Disruption of Mediator rescues the stunted growth of a lignin-deficient Arabidopsis mutant

Lignin is a phenylpropanoid-derived heteropolymer important for the strength and rigidity of the plant secondary cell wall. Genetic disruption of lignin biosynthesis has been proposed as a means to improve forage and bioenergy crops, but frequently results in stunted growth and developmental abnormalities, the mechanisms of which are poorly understood. Here we show that the phenotype of a lignin-deficient Arabidopsis mutant is dependent on the transcriptional co-regulatory complex, Mediator. Disruption of the Mediator complex subunits MED5a (also known as REF4) and MED5b (also known as RFR1) rescues the stunted growth, lignin deficiency and widespread changes in gene expression seen in the phenylpropanoid pathway mutant ref8, without restoring the synthesis of guaiacyl and syringyl lignin subunits. Cell walls of rescued med5a/5b ref8 plants instead contain a novel lignin consisting almost exclusively of p-hydroxyphenyl lignin subunits, and moreover exhibit substantially facilitated polysaccharide saccharification. These results demonstrate that guaiacyl and syringyl lignin subunits are largely dispensable for normal growth and development, implicate Mediator in an active transcriptional process responsible for dwarfing and inhibition of lignin biosynthesis, and suggest that the transcription machinery and signalling pathways responding to cell wall defects may be important targets to include in efforts to reduce biomass recalcitrance.

Growth and Morphogenesis of Azuki Bean Seedlings in Space during SSAF2013 Program

Seedlings of azuki bean were cultivated under microgravity conditions in space during SSAF2013 program, and then growth, morphology, and the cell wall rigidity of their etiolated epicotyls were analyzed. Epicotyls grown on the ground oriented vertical direction, whereas epicotyls grown in space oriented oblique upward direction away from the cotyledons. The length of epicotyls grown in space was varied, but the proportion of seedlings with larger epicotyls was higher than that of the controls. These results indicate that growth and morphology of epicotyls are modified under microgravity conditions in space. On the other hand, the breaking load of epicotyls was analyzed using a spring balance for determination of the cell wall rigidity of epicotyls. The breaking load of epicotyls grown in space tended to be smaller than that of controls. Also, epicotyls grown in space had resistance to bending than the controls. Thus, microgravity affected the cell wall rigidity of epicotyls. Taken together, azuki bean seedlings performed an automorphogenesis and cell wall modification under microgravity conditions. Under microgravity conditions, where plants need not to resist the gravitational force, the body shape and the cell wall rigidity of stems may be modified.

Apical F‐actin‐regulated exocytic targeting of NtPPME1 is essential for construction and rigidity of the pollen tube cell wall

In tip-confined growing pollen tubes, delivery of newly synthesized cell wall materials to the rapidly expanding apical surface requires spatial organization and temporal regulation of the apical F-actin filament and exocytosis. In this study, we demonstrate that apical F-actin is essential for the rigidity and construction of the pollen tube cell wall by regulating exocytosis of Nicotiana tabacum pectin methylesterase (NtPPME1). Wortmannin disrupts the spatial organization of apical F-actin in the pollen tube tip and inhibits polar targeting of NtPPME1, which subsequently alters the rigidity and pectic composition of the pollen tube cell wall, finally causing growth arrest of the pollen tube. In addition to mechanistically linking cell wall construction and apical F-actin, wortmannin can be used as a useful tool for studying endomembrane trafficking and cytoskeletal organization in pollen tubes.

Resistance of plants to gravitational force

Developing resistance to gravitational force is a critical response for terrestrial plants to survive under 1×g conditions. We have termed this reaction "gravity resistance" and have analyzed its nature and mechanisms using hypergravity conditions produced by centrifugation and microgravity conditions in space. Our results indicate that plants develop a short and thick body and increase cell wall rigidity to resist gravitational force. The modification of body shape is brought about by the rapid reorientation of cortical microtubules that is caused by the action of microtubule-associated proteins in response to the magnitude of the gravitational force. The modification of cell wall rigidity is regulated by changes in cell wall metabolism that are caused by alterations in the levels of cell wall enzymes and in the pH of apoplastic fluid (cell wall fluid). Mechanoreceptors on the plasma membrane may be involved in the perception of the gravitational force. In this review, we discuss methods for altering gravitational conditions and describe the nature and mechanisms of gravity resistance in plants.

Infection structure-specific expression of β-1,3-glucan synthase is essential for pathogenicity of Colletotrichum graminicola and evasion of β-glucan-triggered immunity in maize.

β-1,3-Glucan and chitin are the most prominent polysaccharides of the fungal cell wall. Covalently linked, these polymers form a scaffold that determines the form and properties of vegetative and pathogenic hyphae. While the role of chitin in plant infection is well understood, the role of β-1,3-glucan is unknown. We functionally characterized the β-1,3-glucan synthase gene GLS1 of the maize (Zea mays) pathogen Colletotrichum graminicola, employing RNA interference (RNAi), GLS1 overexpression, live-cell imaging, and aniline blue fluorochrome staining. This hemibiotroph sequentially differentiates a melanized appressorium on the cuticle and biotrophic and necrotrophic hyphae in its host. Massive β-1,3-glucan contents were detected in cell walls of appressoria and necrotrophic hyphae. Unexpectedly, GLS1 expression and β-1,3-glucan contents were drastically reduced during biotrophic development. In appressoria of RNAi strains, downregulation of β-1,3-glucan synthesis increased cell wall elasticity, and the appressoria exploded. While the shape of biotrophic hyphae was unaffected in RNAi strains, necrotrophic hyphae showed severe distortions. Constitutive expression of GLS1 led to exposure of β-1,3-glucan on biotrophic hyphae, massive induction of broad-spectrum defense responses, and significantly reduced disease symptom severity. Thus, while β-1,3-glucan synthesis is required for cell wall rigidity in appressoria and fast-growing necrotrophic hyphae, its rigorous downregulation during biotrophic development represents a strategy for evading β-glucan-triggered immunity.

Regulatory effects of exogenous gibberellic acid (GA3) on water relations and CO2 assimilation among grapevine (Vitis vinifera L.) cultivars

Different impacts of exogenous gibberellic acid (GA3) on water relation and CO2 gas exchange in grapevine leaves were studied on four varieties belong to various ecogeographical groups. GA3 treatment resulted in increasing cell wall rigidity in some cultivars and affected the linear correlation between elasticity modulus (‘ɛ’) and relative water content at the turgor loss point (RWCTLC). The response of cultivar ‘Riesling’ agreed with the hypothesis; GA treatment resulted in increasing ‘ɛ’ values (‘ɛ’>12MPa), indicating decreased cell wall elasticity. According to pressure–volume analysis, osmotic potential at full turgor (Π100) in treated ‘Sauvignon Blanc’ vines was higher compared to the controls. Results of analysis demonstrated that the four varieties showed a negative linear correlation between apoplastic water content (AWSD%) and leaf water potential at the turgor loss point (ΨTLP) and a positive linear correlation between AWSD% and RWCTLP. Values of Ci and PN showed a positive exponential correlation; Ci values increased parallel with increasing net CO2 assimilation in a range between 10 and 24Pa of Ci both in control and treated vines. In each cultivar, intrinsic water use efficiency (WUEi) increased at reduced stomatal conductance. GA3 treatment resulted in favourable values of WUEi as expected for cultivar ‘Kadarka’ (group of convarietas pontica). WUEi was significantly (P<0.05) lower in the GA3 treated vines compared to the controls in most of the varieties irrespective of different ecogeographical groups.

A FAST AND ACCURATE HIGH PERFORMANCE LIQUID CHROMATOGRAPHY ASSAY TO QUANTIFY PLASMA CEFTAZIDIME CONCENTRATIONS FOR CLINICAL ROUTINE

Ceftazidime (C22H22N6O7S2) is a beta-lactam antibiotic. [1,2] It is a bactericidal third-generation cephalosporin, acting on the cell wall by inhibiting the action of carboxipeptidase and transpeptidases and preventing peptidoglycan synthesis and cross-linking, which is necessary for keeping the strength and rigidity of the bacterial cell wall. It presents a broad antibacterial spectrum with higher action on Gram-negative bacteria. Pseudomonas aeruginosa is the pathogen responsible for many nosocomial infections in critically ill patients. Ceftazidime is one of the most active antibiotics against P. aeruginosa. The bactericidal activity of ceftazidime and, in general, beta-lactam antibiotics is time dependent. The pharmacokinetic=pharmacodynamic (PK=PD) index that best correlates with clinical efficacy is the time during which the concentration of antibiotic (in steady state: SS) exceeds the minimum inhibitory concentration (MIC) of the bacteria causing the infection. This index can be expressed as T >MIC > 60 70%. [6] It is also recommended that the SS serum concentration (C) of antibiotic has to be above 4–5 times the MIC for the microorganism. Continuous infusion facilitates to optimize both indices ðT >MIC and C > 4 MICÞ compared to bolus administration or intermittent infusion.

Mechano-chemical aspects of organ formation in Arabidopsis thaliana: the relationship between auxin and pectin.

How instructive signals are translated into robust and predictable changes in growth is a central question in developmental biology. Recently, much interest has centered on the feedback between chemical instructions and mechanical changes for pattern formation in development. In plants, the patterned arrangement of aerial organs, or phyllotaxis, is instructed by the phytohormone auxin; however, it still remains to be seen how auxin is linked, at the apex, to the biochemical and mechanical changes of the cell wall required for organ outgrowth. Here, using Atomic Force Microscopy, we demonstrate that auxin reduces tissue rigidity prior to organ outgrowth in the shoot apex of Arabidopsis thaliana, and that the de-methyl-esterification of pectin is necessary for this reduction. We further show that development of functional organs produced by pectin-mediated ectopic wall softening requires auxin signaling. Lastly, we demonstrate that coordinated localization of the auxin transport protein, PIN1, is disrupted in a naked-apex produced by increasing cell wall rigidity. Our data indicates that a feedback loop between the instructive chemical auxin and cell wall mechanics may play a crucial role in phyllotactic patterning.

The plasma membrane proteome of maize roots grown under low and high iron conditions

Iron (Fe) homeostasis is essential for life and has been intensively investigated for dicots, while our knowledge for species in the Poaceae is fragmentary. This study presents the first proteome analysis (LC-MS/MS) of plasma membranes isolated from roots of 18-day old maize (Zea mays L.). Plants were grown under low and high Fe conditions in hydroponic culture. In total, 227 proteins were identified in control plants, whereas 204 proteins were identified in Fe deficient plants and 251 proteins in plants grown under high Fe conditions. Proteins were sorted by functional classes, and most of the identified proteins were classified as signaling proteins. A significant number of PM-bound redox proteins could be identified including quinone reductases, heme and copper-containing proteins. Most of these components were constitutive, and others could hint at an involvement of redox signaling and redox homeostasis by change in abundance. Energy metabolism and translation seem to be crucial in Fe homeostasis. The response to Fe deficiency includes proteins involved in development, whereas membrane remodeling and assembly and/or repair of Fe-S clusters is discussed for Fe toxicity. The general stress response appears to involve proteins related to oxidative stress, growth regulation, an increased rigidity and synthesis of cell walls and adaption of nutrient uptake and/or translocation. This article is part of a Special Issue entitled: Plant Proteomics in Europe.

Effects of salinity on the transcriptome of growing maize leaf cells point at cell-age specificity in the involvement of the antioxidative response in cell growth restriction.

BackgroundSalinity inhibits growth and development of most plants. The response to salinity is complex and varies between plant organs and stages of development. It involves challenges of ion toxicities and deficiencies as well as osmotic and oxidative stresses. The range of functions affected by the stress is reflected in elaborate changes to the transcriptome. The mechanisms involved in the developmental-stage specificity of the inhibitory responses are not fully understood. The present study took advantage of the well characterized developmental progression that exists along the maize leaf, for identification of salinity induced, developmentally-associated changes to the transcriptome. Differential subtraction screening was conducted for cells of two developmental stages: from the center of the growth zone where the expansion rate is highest, and from older cells at a more distal location of the growing zone where the expansion rate is lower and the salinity restrictive effects are more pronounced. Real-Time PCR analysis was used for validation of the expression of selected genes.ResultsThe salinity-induced changes demonstrated an age-related response of the growing tissue, with elevation of salinity-damages with increased age. Growth reduction, similar to the elevation of percentage dry matter (%DM), and Na and Cl concentrations were more pronounced in the older cells. The differential subtraction screening identified genes encoding to proteins involved in antioxidant defense, electron transfer and energy, structural proteins, transcription factors and photosynthesis proteins. Of special interest is the higher induced expression of genes involved in antioxidant protection in the young compared to older cells, which was accompanied by suppressed levels of reactive oxygen species (H2O2 and O2-). This was coupled with heightened expression in the older cells of genes that enhance cell-wall rigidity, which points at reduced potential for cell expansion.ConclusionsThe results demonstrate a cell-age specificity in the salinity response of growing cells, and point at involvement of the antioxidative response in cell growth restriction. Processes involved in reactive oxygen species (ROS) scavenging are more pronounced in the young cells, while the higher growth sensitivity of older cells is suggested to involve effects on cell-wall rigidity and lower protein protection.

Osmotic and elastic adjustments in cold desert shrubs differing in rooting depth: coping with drought and subzero temperatures

Physiological adjustments to enhance tolerance or avoidance of summer drought and winter freezing were studied in shallow- to deep-rooted Patagonian cold desert shrubs. We measured leaf water potential (Ψ(L)), osmotic potential, tissue elasticity, stem hydraulic characteristics, and stomatal conductance (g (S)) across species throughout the year, and assessed tissue damage by subzero temperatures during winter. Species behavior was highly dependent on rooting depth. Substantial osmotic adjustment (up to 1.2MPa) was observed in deep-rooted species exhibiting relatively small seasonal variations in Ψ(L) and with access to a more stable water source, but having a large difference between predawn and midday Ψ(L). On the other hand, shallow-rooted species exposed to large seasonal changes in Ψ(L) showed limited osmotic adjustment and incomplete stomatal closure, resulting in turgor loss during periods of drought. The bulk leaf tissue elastic modulus (ε) was lower in species with relatively shallow roots. Daily variation in g (S) was larger in shallow-rooted species (more than 50% of its maximum) and was negatively associated with the difference between Ψ(L) at the turgor loss point and minimum Ψ(L) (safety margin for turgor maintenance). All species increased ε by about 10MPa during winter. Species with rigid tissue walls exhibited low leaf tissue damage at -20°C. Our results suggest that osmotic adjustment was the main water relationship adaptation to cope with drought during summer and spring, particularly in deep-rooted plants, and that adjustments in cell wall rigidity during the winter helped to enhance freezing tolerance.

Deletion of the Candida albicans PIR32 Results in Increased Virulence, Stress Response, and Upregulation of Cell Wall Chitin Deposition

Candida albicans is a common opportunistic pathogen that causes a wide variety of diseases in a human immunocompromised host leading to death. In a pathogen, cell wall proteins are important for stability as well as for acting as antigenic determinants and virulence factors. Pir32 is a cell wall protein and member of the Pir protein family previously shown to be upregulated in response to macrophage contact and whose other member, Pir1, was found to be necessary for cell wall rigidity. The purpose of this study is to characterize Pir32 by generating a homozygous null strain and comparing the phenotype of the null with that of the wild-type parental strain as far as filamentation, virulence in a mouse model of disseminated candidiasis, resistance to oxidative stress and cell wall disrupting agents, in addition to adhesion, biofilm capacities, and cell wall chitin content. Our mutant was shown to be hyperfilamentous, resistant to sodium dodecyl sulfate, hydrogen peroxide, sodium chloride, and more virulent in a mouse model when compared to the wild type. These results were unexpected, considering that most cell wall mutations weaken the wall and render it more susceptible to external stress factors and suggests the possibility of a cell surface compensatory mechanism. As such, we measured cell wall chitin deposition and found a twofold increase in the mutant, possibly explaining the above-observed phenotypes.

Alleviation of Al-toxicity in wheat by boron 1. Anatomical and ultrastructure effects of aluminium on root of aluminium-tolerant cultivar ofTriticum aestivum

The effect of aluminium was investigated on the seedlings pre-treated by two concentrations of boron 4 μM or 32 μM grown in water culture using a concentration of 500 μM Al for 3 days. Semithin and ultrathin sections of the apical region of the roots and transmission electron microscopy micrographs were analysed of fourteen-day-old Al-tolerant (‘Sakha 93’) cultivar of Triticum aestivum. Results showed that the amelioration effect of boron treatment was pronounced at 32 μM B level. Rigidity of cell wall and plasma membrane in the wheat root apex cells (Zone of root hairs) could result from the formation of bonds of ions of the toxicant with components within their structures and appears as dark precipitants in cross sections. Cross sections of the apical region of the control plant roots showed well-developed normal anatomical structure and cell ultrastructure typical for those of root regions. Slight alterations under the influence of aluminium or boron alone or both of them and the role exhibited by boro...

EFFECT OF THE APPLICATION OF SILICON HYDROXIDE ON YIELD AND QUALITY OF CHERRY TOMATO

Silicon (Si) plays an important role in the structural rigidity of cell walls. When plants have a passive or selective assimilation or they are poor accumulators as solanaceae, the percentage of silicon absorbed and present in the plants is lower than 1%, but its presence can provide significant benefits to the plant before it undergoes biotic and abiotic stresses. The objective of this work was to assess the effect of fertilization with monosilicic acid on yield and quality of cherry tomato crops (Lycopersicon esculentum var. cerasiforme cv. ‘Salomee’) grown on rockwool in a greenhouse. Two types of treatments were investigated: control test (conventional fertilization) and fertilization with silicic acid [Si(OH)4] [seven applications of 250 mL of Si(OH)4·ha−1 for each crop cycle]. Significant differences were observed, including a higher number of fruits (fruits/plant) and a larger yield (kg m−2) in the plots that were fertilized with silicon.

Objectives, Outlines, and Preparation for the Resist Tubule Space Experiment to Understand the Mechanism of Gravity Resistance in Plants

Gravity resistance is a principal graviresponse in plants. In resistance to hypergravity, the gravity signal may be perceived by the mechanoreceptors located on the plasma membrane, and then transformed and transduced via the structural continuum or physiological continuity of cortical microtubules-plasma membrane-cell wall, leading to an increase in the cell wall rigidity as the final response. The Resist Tubule experiment, which will be conducted in the Kibo Module on the International Space Station, aims to confirm that this hypothesis is applicable to resistance to 1 G gravity. There are two major objectives in the Resist Tubule experiment. One is to quantify the contributions of cortical microtubules to gravity resistance using Arabidopsis tubulin mutants with different degrees of defects. Another objective is to analyze the modifications to dynamics of cortical microtubules and membrane rafts under microgravity conditions on-site by observing green fluorescent protein (GFP)-expressing Arabidopsis lines with the fluorescence microscope in the Kibo. We have selected suitable mutants, developed necessary hardware, and fixed operation procedure for the experiment.

Antifungal thiopeptide cyclothiazomycin B1 exhibits growth inhibition accompanying morphological changes via binding to fungal cell wall chitin

Cyclothiazomycin B1 (CTB1) is an antifungal cyclic thiopeptide isolated from the culture broth of Streptomyces sp. HA 125-40. CTB1 inhibited the growth of several filamentous fungi including plant pathogens along with swelling of hyphae and spores. The antifungal activity of CTB1 was weakened by hyperosmotic conditions, and hyphae treated with CTB1 burst under hypoosmotic conditions, indicating increased cell wall fragility. CTB1-sensitive fungal species contain high levels of cell wall chitin and/or chitosan. Unlike nikkomycin Z, a competitive inhibitor of chitin synthase (CHS), CTB1 did not inhibit CHS activity. Although CTB1 inhibited CHS biosynthesis, the same result was also obtained with a non-specific proteins inhibitor, cycloheximide, which did not reduce cell wall rigidity. These results indicate that the primary target of CTB1 is not CHS, and we concluded that CTB1 antifungal activity was independent of this sole inhibition. We found that CTB1 bound to chitin but did not bind to β-glucan and chitosan. The results of the present study suggest that CTB1 induces cell wall fragility by binding to chitin, which forms the fungal cell wall. The antifungal activity of CTB1 could be explained by this chitin-binding ability.