Bacterium Erwinia Chrysanthemi Research Articles

Hypersensitivity Reactions to Native E. coli L-Asparaginase in Children with Acute Lymphoblastic Leukemia May Vary By Treatment Schedule and Type of Glucocorticoid in Induction: Results of Trial ALL-BFM 2000

Background: Asparaginase (ASNase) has become a key component of treatment for acute lymphoblastic leukemia (ALL). The ability of this agent to eliminate leukemic blasts by utilizing the special feature that such cells are largely unable to synthesize the otherwise non-essential amino acid asparagine means that blasts cannot survive in an environment in which this amino acid has been depleted. Currently, there are three ASNase products commercially available sharing the same mechanism of action. The oldest one is the purified native enzyme extracted from E. coli. This product was further developed and refined by conjugation with polyethylene glycol (PEG-L-Asparaginase, PEG-ASNase) to prolong half-life and to reduce immunogenicity. A third ASNase product derived from the bacterium Erwinia chrysanthemi (Erwinase) is structurally different from the E. coli ASNase products. The main reason for limitation in the use of ASNase is the rather frequent occurrence of hypersensitivity reactions (HSR). Such reactions require the replacement of the ASNase product used with alternative preparations. The incidence of clinical HSR to ASNase varies with the type of ASNase product, the treatment schedule (number of ASNase doses, extended ASNase-free intervals) and the administration route (intravenously [IV] or intramuscularly [IM]). This retrospective study was primarily performed to demonstrate the dynamics and the interdependence when using ASNase in a complex multiagent treatment protocol. It aimed to evaluate the incidence of clinically apparent HSR in the ALL-BFM 2000 trial which was part of the cooperative trial AIEOP-BFM ALL 2000. Methods: Clinical hypersensitivity reactions (HSR) to native E. coli ASNase were retrospectively analyzed in a cohort of children with acute lymphoblastic leukemia (ALL) focusing on the impact of concurrent chemotherapy schedules in the risk-adapted and randomized treatment protocol and evaluating the prognostic relevance of asparaginase discontinuation. Patients: Patients with ALL aged 1-18 years were treated risk-stratified with standard-risk (SR), medium-risk (MR) and high-risk (HR) regimens in trial ALL-BFM 2000. Schedule of intravenously administered native E. coli ASNase varied by risk group and randomization arm. Randomizations compared the glucocorticoids prednisolone and dexamethasone in induction and different reintensification regimens (Möricke A et al, BLOOD 127(17): 2101-2112 (2016)). In this trial, native E. coli ASNase was administered IV as first-line product during the induction and reinduction phases. In the high-risk arm, the phase of intensified consolidation included additional E. coli ASNase doses. PEG-ASNase (IV) or Erwinase (IM) were used as second- or third-line products after HSR occurring with native E. coli ASNase or the respective second-line product. Results: HSR occurred in 40% (492/1207) of all evaluable patients. One-year cumulative incidence (CI-HSR±standard error) was 42.3±1.5% (40.6±2.5% in SR, 37.0±1.9% in MR, 65.2±3.8% in HR). Dexamethasone-treated SR and MR patients had significantly higher CI-HSR (48.5±4.3% and 45.9±3.2%) than prednisolone-treated patients (32.3±3.7% [p=0.007] and 31.2±2.9% [p<0.001]); no such difference was seen among HR patients who underwent multiple exposures to the drug (Fig. 1). Post-induction randomizations showed that one week of dexamethasone before asparaginase re-exposition in reinduction did not protect from clinical HSR in the SR/MR arm. Randomization in HR revealed an effect of the type of concurrent chemotherapeutic drugs on the risk of HSR. Discontinuation of ASNase occurred in 6.1% of all patients. No disadvantage in leukemia outcome could be detected for these patients. Conclusion: The results in our study demonstrate the complex interdependencies contributing to the risk of HSR to E. coli asparaginase in a multiagent chemotherapy protocol. The differential effects of dexamethasone and prednisolone in induction generated new hypotheses about the role of glucocorticoids in sensitization or achievement of immune tolerance to asparaginase. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Biodegradation of the Azo Dye Airedale Yellow CHD: Understanding using residuals

Textile industries are heavy users of water and also produce lots of contaminated effluents. The main contaminants are azo dyes. Hence, the effluents are to be treated before leaving in the environment. In this study, the azo dye Airedale Yellow CHD was biodegraded using two bacteria Thalassospira frigidphilosprofundus (NCIM no 5438) and Erwinia chrysanthemi Burkholder (NCIM no 5213) in shaking conical flasks. Effect of Various parameters like pH, temperature, agitation, and concentration of dye solution on its decolorization was investigated. The biodegradation was statistically worked out using MINITAB software for the ANOVA. The residual plots along with the scatter plots for the decolorization of Airedale Yellow CHD using T. frigidphilosprofundus and E. chrysanthemi Burkholder are also obtained and included in this work. The maximum percent removal of the azo dye was obtained by using T. frigidphilosprofundus (77.41%) whereas it was reported at 74.64% by using E. chrysanthemi Burkholder. The obtained results formed a good fit according to the obtained normal residual plot which can conclude that the findings of the study are accurate and satisfactory.

The effect of Yarrowia lipolytical-asparaginase on apoptosis induction and inhibition of growth in Burkitt's lymphoma Raji and acute lymphoblastic leukemia MOLT-4 cells

l-Asparaginase (l-asparagine amidohydrolase; E.C.3.5.1.1) as an anticancer agent is used to treat acute lymphocytic leukemia (ALL), Human Burkitt's lymphoma and non-Hodgkin's lymphoma. The commercial asparaginases are obtained from bacteria Erwinia chrysanthemi and Escherichia coli now which had many side effects. In this study, the effects of a novel l-asparaginase from yeast Yarrowia lipolytica was investigated on human ALL and Burkitt's lymphoma cell lines. The l-asparaginase causes metabolic stress, cytotoxicity, and apoptosis due to the arrest of the G0 cell cycle, the activation of caspase-3 and the modulation of mitochondrial membrane integrity. The RT-PCR analysis showed a significant increase in the pro-apoptosis genes such as Bax, Caspase-3, Caspase-8, Caspase-9 and p53 (P < 0.05) while the anti-apoptotic marker Bcl-2 was significantly decreased (P < 0.05). Furthermore, Y. lipolytical-asparaginase causes autophagy and increased ROS. The l-asparaginase has cytotoxic and anticancer effects higher than commercial asparaginase. In conclusion, Y. lipolytical-asparaginase shows interesting anticancer activity and it can be introduced as a new eukaryotic and therapeutic agent and strategy for ALL and Burkitt's lymphoma treatment after the in vivo and clinical experiments.

Antibiotic potential of Lunularia cruciata (L.) Dum ex. Lindb (bryophyta) of Kumaon Himalaya

Antibiotic activity of Lunularia cruciata was tested against five pathogenic bacteria (Agrobacterium tumefaciens, Xanthomonas phoseoli, Escherichia coli, Bacillus subtilis and Erwinia chrysanthemi) and three pathogenic fungi (Alternaria alternata, Sclerotinia sclerotiorum and Pyricularia oryzae). The plant extract was prepared in various solvents (ethanol, methanol, acetone, chloroform and water). All the crude organic extracts of L. cruciata showed substantial antibacterial activity while antifungal activity was not found against any of the fungal strains tested. The aqueous extract of the plant did not exhibit any antimicrobial activity. The ethanol extract showed maximum growth inhibition against the test microorganisms (A. tumefaciens, X. phoseoli, E. coli and B. subtilis; ZOI = 10 to 20 mm) followed by methanol, acetone and chloroform extracts (ZOI = 8 to 12 mm). The inhibitory activity of these extracts was found very effective against bacteria compared to standard antibiotic ampicillin (10 mcg) used as positive control.

Structure and Function of ELIC Bound with the Antagonist Acetylcholine

The bacterium Erwinia chrysanthemi ligand gated ion channel (ELIC) is a prototype for Cys-loop receptors, including nicotinic acetylcholine receptors (nAChRs). We co-crystallized ELIC with acetylcholine, an endogenous agonist of nAChRs, and solved the crystal structure to a resolution of 2.9 A. Acetylcholine binds to the orthosteric agonist site for Cys-loop receptors. Upon acetylcholine binding, loop C exhibits a substantial contraction with a profound reduction in flexibility. Conformational changes in nearby regions of the ligand-binding domain are also observed. However, no substantial reorganization in the pore region was identified except for subtle side chain reorientation of the pore constriction residue F247. Functional measurements on Xenopus oocytes expressing ELIC channels indicate that acetylcholine antagonizes the ELIC currents elicited by primary amines. Our high-resolution structure provides an atomic-level detailed picture of how ligand binding renders gating-related conformational changes in different domains of Cys-loop receptors. It also represents a valuable template for rational drug development. (Supported by NIH grants R01GM066358, R01GM056257, R37GM049202, and T32GM075770)

Structural basis for substrate recognition by Erwinia chrysanthemi GH30 glucuronoxylanase

Xylanase A from the phytopathogenic bacterium Erwinia chrysanthemi is classified as a glycoside hydrolase family 30 enzyme (previously in family 5) and is specialized for degradation of glucuronoxylan. The recombinant enzyme was crystallized with the aldotetraouronic acid β-D-xylopyranosyl-(1→4)-[4-O-methyl-α-D-glucuronosyl-(1→2)]-β-D-xylopyranosyl-(1→4)-D-xylose as a ligand. The crystal structure of the enzyme-ligand complex was solved at 1.39 Å resolution. The ligand xylotriose moiety occupies subsites -1, -2 and -3, whereas the methyl glucuronic acid residue attached to the middle xylopyranosyl residue of xylotriose is bound to the enzyme through hydrogen bonds to five amino acids and by the ionic interaction of the methyl glucuronic acid carboxylate with the positively charged guanidinium group of Arg293. The interaction of the enzyme with the methyl glucuronic acid residue appears to be indispensable for proper distortion of the xylan chain and its effective hydrolysis. Such a distortion does not occur with linear β-1,4-xylooligosaccharides, which are hydrolyzed by the enzyme at a negligible rate. Structural and experimental data are available in the Protein Data Bank database under accession number 2y24 [45].

English

Various organic and aqueous extracts of aerial part of Boenninghausenia albiflora (Rutaceae) obtained by infusion and maceration were screened for their antimicrobial activity against eight animal and plant pathogenic bacteria (Bacillus subtilis, Staphylococcus aureus, Erwinia chrysanthemi, Escherichia coli, Proteus vulgaris, Xanthomonas phaseoli, Agrobacterium tumefaciens and Xanthomonas campestris) using disc diffusion method. Out of total 32 tests performed, 27 tests showed positive antibacterial activity at 1000 mg/ml concentration, whereas 15 instances exhibited zone of inhibition ³ 10 mm at same concentration. The activity shown by some of the extracts was found higher than ampicillin (10 mcg) and erythromycin (15 mcg), standard antibiotic used.

X-ray structure of a prokaryotic pentameric ligand-gated ion channel

Pentameric ligand-gated ion channels (pLGICs) are key players in the early events of electrical signal transduction at chemical synapses. The family codes for a structurally conserved scaffold of channel proteins that open in response to the binding of neurotransmitter molecules. All proteins share a pentameric organization of identical or related subunits that consist of an extracellular ligand-binding domain followed by a transmembrane channel domain. The nicotinic acetylcholine receptor (nAChR) is the most thoroughly studied member of the pLGIC family (for recent reviews see refs 1-3). Two sources of structural information provided an architectural framework for the family. The structure of the soluble acetylcholine-binding protein (AChBP) defined the organization of the extracellular domain and revealed the chemical basis of ligand interaction. Electron microscopy studies of the nAChR from Torpedo electric ray have yielded a picture of the full-length protein and have recently led to the interpretation of an electron density map at 4.0 A resolution. Despite the wealth of experimental information, high-resolution structures of any family member have so far not been available. Until recently, the pLGICs were believed to be only expressed in multicellular eukaryotic organisms. The abundance of prokaryotic genome sequences, however, allowed the identification of several homologous proteins in bacterial sources. Here we present the X-ray structure of a prokaryotic pLGIC from the bacterium Erwinia chrysanthemi (ELIC) at 3.3 A resolution. Our study reveals the first structure of a pLGIC at high resolution and provides an important model system for the investigation of the general mechanisms of ion permeation and gating within the family.

Integration of two essential virulence modulating signals at theErwinia chrysanthemi pelgene promoters: a role for Fis in the growth‐phase regulation

Production of the essential virulence factors, called pectate lyases (Pels), in the phytopathogenic bacterium Erwinia chrysanthemi is controlled by a complex regulation system and responds to various stimuli, such as the presence of pectin or plant extracts, growth phase, temperature and iron concentration. The presence of pectin and growth phase are the most important signals identified. Eight regulators modulating the expression of the pel genes (encoding Pels) have been characterized. These regulators are organized in a network allowing a sequential functioning of the regulators during infection. Although many studies have been carried out, the mechanisms of control of Pel production by growth phase have not yet been elucidated. Here we report that a fis mutant of E. chrysanthemi showed a strong increase in transcription of the pel genes during exponential growth whereas induction of expression in the parental strain occurred at the end of exponential growth. This reveals that Fis acts to prevent an efficient transcription of pel genes at the beginning of exponential growth and also provides evidence of the involvement of Fis in the growth-phase regulation of the pel genes. By using in vitro DNA-protein interactions and transcription experiments, we find that Fis directly represses the pel gene expression at the transcription initiation step. In addition, we show that Fis acts in concert with KdgR, the main repressor responding to the presence of pectin compounds, to shut down the pel gene transcription. Finally, we find that active Fis is required for the efficient translocation of the Pels in growth medium. Together, these data indicate that Fis tightly controls the availability of Pels during pathogenesis by acting on both their production and their translocation in the external medium.

Snakin-2, an antimicrobial peptide from potato whose gene is locally induced by wounding and responds to pathogen infection.

The peptide snakin-2 (StSN2) has been isolated from potato (Solanum tuberosum cv Jaerla) tubers and found to be active (EC(50) = 1-20 microM) against fungal and bacterial plant pathogens. It causes a rapid aggregation of both Gram-positive and Gram-negative bacteria. The corresponding StSN2 cDNA encodes a signal sequence followed by a 15-residue acidic sequence that precedes the mature StSN2 peptide, which is basic (isoelectric point = 9.16) and 66 amino acid residues long (molecular weight of 7,025). The StSN2 gene is developmentally expressed in tubers, stems, flowers, shoot apex, and leaves, but not in roots, or stolons, and is locally up-regulated by wounding and by abscisic acid treatment. Expression of this gene is also up-regulated after infection of potato tubers with the compatible fungus Botritys cinerea and down-regulated by the virulent bacteria Ralstonia solanacearum and Erwinia chrysanthemi. These observations are congruent with the hypothesis that the StSN2 is a component of both constitutive and inducible defense barriers.

The Oligogalacturonate-specific Porin KdgM of Erwinia chrysanthemi Belongs to a New Porin Family

The phytopathogenic Gram-negative bacteria Erwinia chrysanthemi secretes pectinases, which are able to degrade the pectic polymers of plant cell walls, and uses the degradation products as a carbon source for growth. We characterized a major outer membrane protein, KdgM, whose synthesis is strongly induced in the presence of pectic derivatives. The corresponding gene was characterized. Analysis of transcriptional fusions showed that the kdgM expression is controlled by the general repressor of pectinolytic genes, KdgR, by the repressor of hexuronate catabolism genes, ExuR, by the pectinase gene repressor, PecS, and by catabolite repression via the cyclic AMP receptor protein (CRP) transcriptional activator. A kdgM mutant is unable to grow on oligogalacturonides longer than trimers, and its virulence is affected. Electrophysiological experiments with planar lipid bilayers showed that KdgM behaves like a voltage-dependent porin that is slightly selective for anions and that exhibits fast block in the presence of trigalacturonate. In contrast to most porins, KdgM seems to be monomeric. KdgM has no homology with currently known porins, but proteins similar to KdgM are present in several bacteria. Therefore, these proteins might constitute a new family of porin channels.

H-NS-dependent activation of pectate lyases synthesis in the phytopathogenic bacterium Erwinia chrysanthemi is mediated by the PecT repressor.

Production of the main virulence determinant pectate lyases (Pels) of the phytopathogenic bacterium Erwinia chrysanthemi is modulated by a complex regulatory network involving the repressor proteins KdgR, PecS and PecT and the activator systems Pir, ExpI-ExpR and CRP. Of these regulators, CRP and PecT are particularly important since the absence of CRP or a slight overproduction of PecT leads to a drastic reduction in synthesis of Pel species. Recently, it has been shown that production of Pel species is strongly reduced in an E. chrysanthemi hns mutant, suggesting an activator function of the nucleoid-associated protein H-NS in the expression of the pel genes. Here, we report that the reduced synthesis of Pel species in the hns mutant results from a negative control, exerted by H-NS, on the transcription of the regulatory gene pecT. This H-NS/PecT cascade regulation is one of the first elucidations of a positive effect of H-NS on target gene expression. Moreover, we found that H-NS also represses the expression of expI, expR and pel genes. H-NS control is the result of H-NS binding to extended regions within the pecT, expI, expR and pel genes. Investigation of the simultaneous binding of CRP, RNA polymerase (RNAP) and H-NS on the pelD gene revealed that these three proteins form a nucleoprotein com-plex. Together, these data indicate that, by exerting a negative control at multiple levels, H-NS plays a crucial role in the E. chrysanthemi pel regulatory network.

Identification of TogMNAB, an ABC transporter which mediates the uptake of pectic oligomers in Erwinia chrysanthemi 3937.

The bacterium Erwinia chrysanthemi, which causes soft rot disease on various plants, is able to use pectin as a carbon source for growth. Knowledge of the critical step in pectin catabolism which allows the entry of pectic oligomers into the cells is scarce. We report here the first example of a transport system involved in the uptake of pectic oligomers. The TogMNAB transporter of E. chrysanthemi is a member of the ATP-binding cassette (ABC) superfamily. TogM and TogN are homologous to the inner membrane components, TogA exhibits the signature of ABC ATPases and TogB shows similarity with periplasmic ligand-binding proteins. The TogMNAB transporter is a new member of the carbohydrate uptake transporter-1 family (CUT1, TC no. 3.1.1), which is specialized in the transport of complex sugars. The four genes, togM, togN, togA and togB, are apparently co-transcribed in a large operon which also includes the pectate lyase gene pelW. The transcription of the tog operon is induced in the presence of pectic derivatives and is affected by catabolite repression. It is controlled by the KdgR repressor and the CRP activator. The TogMNAB system is able to provide Escherichia coli with the ability to transport oligogalacturonides. In E. chrysanthemi, the TogMNAB system seems to play a major role in switching on the induction of pectin catabolism. TogB also acts as a specific receptor for chemotaxis towards oligogalacturonides. The decreased capacity of maceration of a togM mutant indicates the importance of transport and/or attraction of oligogalacturonides for E. chrysanthemi pathogenicity.

Erwinia chrysanthemi strains cause death of human gastrointestinal cells in culture and express an intimin-like protein.

The bacterium Erwinia chrysanthemi is a model plant pathogen, responsible for causing cell death in plant tissue. Cell-wall depolymerizing enzymes and avirulence proteins essential for parasitism by this bacterium utilize dedicated type II and type III secretion systems, respectively. Although E. chrysanthemi is not recognized as a mammalian pathogen, we have observed that the bacterium can adhere to, cause an oxidative stress response in and kill cultured human adenocarcinoma cells. These bacteria express a surface protein that bears immunological identity to intimin, a protein required for full virulence of enterohemorrhagic and enteropathogenic Escherichia coli. A type III secretion mutant of E. chrysanthemi was observed to have a significantly lower capability of causing death than the wild-type strain in parallel cultures of human colon adenocarcinoma cells. These observations suggest that E. chrysanthemi has the potential to parasitize mammalian hosts as well as plants.

Erwinia chrysanthemi strains cause death of human gastrointestinal cells in culture and express an intimin-like protein

The bacterium Erwinia chrysanthemi is a model plant pathogen, responsible for causing cell death in plant tissue. Cell-wall depolymerizing enzymes and avirulence proteins essential for parasitism by this bacterium utilize dedicated type II and type III secretion systems, respectively. Although E. chrysanthemi is not recognized as a mammalian pathogen, we have observed that the bacterium can adhere to, cause an oxidative stress response in and kill cultured human adenocarcinoma cells. These bacteria express a surface protein that bears immunological identity to intimin, a protein required for full virulence of enterohemorrhagic and enteropathogenic Escherichia coli. A type III secretion mutant of E. chrysanthemi was observed to have a significantly lower capability of causing death than the wild-type strain in parallel cultures of human colon adenocarcinoma cells. These observations suggest that E. chrysanthemi has the potential to parasitize mammalian hosts as well as plants.

External pH: an environmental signal that helps to rationalize pel gene duplication in Erwinia chrysanthemi.

The phytopathogenic bacterium Erwinia chrysanthemi produces five major pectate lyases that are key virulence factors in soft-rot disease development. Using transcriptional fusions, we studied the regulation of pelA, pelD, and pelE gene expression as a function of variation of the external pH. pelA and pelD were expressed when bacteria were grown in an acidic medium while pelE was transcribed only in basic medium. Using phenol red, we observed that, in chicory leaves, pH value of infected tissue varies from acidic to basic. Taken together, these findings are discussed in the context of a model unifying both catalysis and regulation to account for pel gene evolution. In particular, we propose that the three isoenzymes are produced sequentially during the infection process.

Cloning and sequencing of pel gene responsible for CMCase activity from Erwinia chrysanthemi PY35.

The phytopathogenic bacterium Erwinia chrysanthemi secretes multiple isozymes of plant cell wall disrupting enzymes such as pectate lyase and endoglucanase. We cloned genomic DNA from Erwinia chrysanthemi PY35. One of the E. coli XL1-Blue clones contained a 5.1-kb BamHI fragment and hydrolyzed carboxymethyl cellulose and polygalacturonic acid. By subsequent subcloning, we obtained a 2.9-kb fragment (pPY100) that contained the pel gene responsible for CMCase and pectate lyase activities. The pel gene had an open reading frame (ORF) of 1,278 bp encoding 425 amino acids with a signal peptide of 25 amino acids. Since the deduced amino acid sequence of this protein was very similar to that of PelL of E. chrysanthemi EC16, we concluded that it belonged to the pectate lyase family EC 4.2.2.2, and we designated it PelL1. Sequencing showed that the PeIL1 protein contains 400 amino acids and has a calculated pI of 7.15 and a molecular mass of 42,925 Da. The molecular mass of PelL1 protein expressed in E. coli XL1-Blue, as analyzed by SDS-PAGE, appeared to be 43 kDa. The optimum pH for its enzymatic activity was 9, and the optimum temperature was about 40 decreased C.

Engineering, expression and biochemical characterization of the hemoglobin domain of a Erwinia chrysanthemi flavohemoprotein.

An artificial hemoglobin-like domain has been constructed by engineering the gene coding for the multi-domain flavohemoprotein from the bacterium Erwinia chrysanthemi. This domain was designed by molecular modelling, cloned and over-expressed in Escherichia coli. The holo-protein was obtained in large quantities after extraction from inclusion bodies and refolding in presence of alkaline hemin. The purified 140-residue domain was studied and characterized to gain new insights into the biochemical function of the recombinant domain and the biological role of this new flavohemoprotein. The structural and functional features of this domain in solution were studied using far-ultraviolet circular dichroism, resonance Raman, proton-NMR spectroscopy, flash laser photolysis and molecular modelling. The recombinant domain is shown to be folded properly and active. This hemoglobin-like domain is able to bind oxygen and carbon monoxide with very high affinity. It exhibits a rapid auto-oxidation which may explain its tight association with a flavin containing reductase domain. A functional model of this hemoglobin is discussed and compared with the X-ray structures of other hemoproteins.

Endogenous cellulases in animals: isolation of beta-1, 4-endoglucanase genes from two species of plant-parasitic cyst nematodes.

beta-1,4-Endoglucanases (EGases, EC 3.2.1.4) degrade polysaccharides possessing beta-1,4-glucan backbones such as cellulose and xyloglucan and have been found among extremely variegated taxonomic groups. Although many animal species depend on cellulose as their main energy source, most omnivores and herbivores are unable to produce EGases endogenously. So far, all previously identified EGase genes involved in the digestive system of animals originate from symbiotic microorganisms. Here we report on the synthesis of EGases in the esophageal glands of the cyst nematodes Globodera rostochiensis and Heterodera glycines. From each of the nematode species, two cDNAs were characterized and hydrophobic cluster analysis revealed that the four catalytic domains belong to family 5 of the glycosyl hydrolases (EC 3.2.1, 3.2.2, and 3.2.3). These domains show 37-44% overall amino acid identity with EGases from the bacteria Erwinia chrysanthemi, Clostridium acetobutylicum, and Bacillus subtilis. One EGase with a bacterial type of cellulose-binding domain was identified for each nematode species. The leucine-rich hydrophobic core of the signal peptide and the presence of a polyadenylated 3' end precluded the EGases from being of bacterial origin. Cyst nematodes are obligatory plant parasites and the identified EGases presumably facilitate the intracellular migration through plant roots by partial cell wall degradation.

Biochemical characterization of the pectate lyase PelZ of Erwinia chrysanthemi 3937

To degrade the plant pectin, the phytopathogenic bacterium Erwinia chrysanthemi produces a set of at least seven endo-pectate lyases (Pels). Five major (PelA, PelB, PelC, PelD and PelE) and two minor isoenzymes (PelL and PelZ) have been identified. PelZ is an extracellular enzyme secreted by the Out system. According to its amino acid sequence, the PelZ protein belongs to a new family. The PelZ protein was overproduced in E. coli and purified to compare its enzymatic properties to that of the other Pels of E. chrysanthemi. PelZ exhibits a low specific activity but good affinity for the substrates including partially methylated pectins (up to 45% methylation). The main characteristic of PelZ is the requirement for both Ca 2+ and Mn 2+ as cofactors while the other Pels require only Ca 2+. The cooperative effect of these two cations suggests the presence of distinct binding sites. The PelZ activity is sensitive to inhibition by excess of substrate, by oligogalacturonides, by the ionic strength and by different plant compounds. PelZ was shown to act in synergy with the major isoenzyme PelE, while competition was observed between PelZ and the minor pectate lyase PelL. No synergistic action was observed between PelZ and PelA, PelB, PelC or PelD.