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To depolymerize plant pectin, the phytopathogenic enterobacterium Erwinia chrysanthemi produces a series of enzymes which include a pectin-methyl-esterase encoded by the pem gene and five isoenzymes of pectate lyases encoded by the five genes pelA, pelB, pelC, pelD, and pelE. We have constructed transcriptional fusions between the pectinase gene promoters and the uidA gene, encoding beta-glucuronidase, to study the regulation of these E. chrysanthemi pectinase genes individually. The transcription of the pectinase genes is dependent on many environmental conditions. All the fusions were induced by pectic catabolic products and responded, to different degrees, to growth phase, catabolite repression, temperature, and nitrogen starvation. Transcription of pelA, pelD, and pelE was also increased in anaerobic growth conditions. High osmolarity of the culture medium increased expression of pelE but decreased that of pelD; the other pectinase genes were not affected. The level of expression of each gene was different. Transcription of pelA was very low under all growth conditions. The expression of the pelB, pelC, and pem genes was intermediate. The pelE gene had a high basal level of expression. Expression of pelD was generally the most affected by changes in culture conditions and showed a low basal level but very high induced levels. These differences in the expression of the pectinase genes of E. chrysanthemi 3937 presumably reflect their role during infection of plants, because the degradation of pectic polymers of the plant cell walls is the main determinant of tissue maceration caused by soft rot erwiniae.
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PMID:Environmental conditions affect transcription of the pectinase genes of Erwinia chrysanthemi 3937. 144 47

The soft-rotting bacterium, Erwinia carotovora subsp. carotovora 71, produces extracellular enzymes such as pectate lyase isozymes (Pels), cellulase (Cel), polygalacturonase (Peh), and protease (Prt). While the extracellular levels of these enzymes are extremely low when the bacterium is grown in salts-yeast extract-glycerol (SYG) medium, the enzymatic activities are highly induced in SYG medium supplemented with celery extract. By transposon (mini-Tn5) mutagenesis, we isolated a RsmA- mutant, AC5070, which overproduces extracellular enzymes; the basal levels of Pel, Peh, and Cel in AC5070 are higher than the induced levels in the RsmA+ parent, AC5047. While Peh production is mostly constitutive in AC5070, Pel, Cel, and Prt production is still inducible with celery extract. The high basal levels of pel-1, pel-3, and peh-1 mRNAs in AC5070 demonstrate that overproduction of the pectolytic enzymes is due to the stimulation of transcription. Using chromosomal DNA flanking mini-Tn5 as a probe, we cloned the wild-type rsmA+ allele, which suppresses Pel, Peh, Cel, and Prt production in both RsmA+ and RsmA- strains. The RsmA- mutant, like its parent, produces N-(3-oxohexanoyl)-L-homoserine lactone (HSL), a starvation/cell density-sensing signal required for extracellular enzyme production. To examine the role of HSL, we constructed HSL-deficient strains by replacing hslI, a locus required for HSL production, with hslI::Tn3HoHo1-Spc. While the basal levels of Pel, Peh, Cel, and Prt are comparable in the RsmA- mutant and its HSL- derivative, these enzymes are barely detectable in the Hsl- derivative of the RsmA+ parent strain.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Inactivation of rsmA leads to overproduction of extracellular pectinases, cellulases, and proteases in Erwinia carotovora subsp. carotovora in the absence of the starvation/cell density-sensing signal, N-(3-oxohexanoyl)-L-homoserine lactone. 764 31

To depolymerize plant pectin, the phytopathogenic enterobacterium Erwinia chrysanthemi produces five isoenzymes of pectate lyases encoded by the five genes pelA, pelB, pelC, pelD and pelE. In Er. chrysanthemi, all genes involved in pectin degradation are specifically controlled by the KdgR repressor and are induced in the presence of a pectin catabolic product, 2-keto-3-deoxygluconate (KDG). transcription of the pectinase genes is dependent on many environmental conditions. Transcriptional fusions present on low-copy-number plasmids were used to study the regulation of the pel genes in a heterologous host, Escherichia coli. Some physiological regulations that take place in Er. chrysanthemi are conserved in E. coli. The five pel fusions in E. coli are affected by growth phase, catabolite repression and anaerobic growth conditions and are induced in the presence of galacturonate, a sugar whose catabolism leads to the formation of KDG, the inducer of pel transcription in Er. chrysanthemi. Expression of pelE increased with the osmolarity of the culture medium. In contrast, the regulation of pel expression by temperature or nitrogen starvation, observed in Er. chrysanthemi, was not conserved in E. coli, suggesting that the mechanisms responsible for these regulations are specific to Er. chrysanthemi. Analysis of different E. coli mutants allowed some regulators affecting the transcription of the pel genes to be identified. In E. coli, the growth-phase regulation of the pel genes is not dependent on the RpoS sigma factor and the fnr gene is not involved in the increase of pel expression in oxygen-limited conditions. The gene hns, involved in the regulation of numerous genes, appears to affect pel expression but the effects of E. coli hns mutations are not related to osmoregulation. In contrast, this analysis clearly demonstrates the interchangeability of two regulatory systems of E. coli and Er. chrysanthemi: the global control exerted by the catabolite activator protein CAP and the specific regulation mediated by the KdgR repressor.
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PMID:Regulatory systems modulating the transcription of the pectinase genes of Erwinia chrysanthemi are conserved in Escherichia coli. 882 30

Erwinia chrysanthemi 3937 secretes five major isoenzymes of pectate lyases encoded by the pel4, pelB, pelC, pelD, and pelE genes and a set of secondary pectate lyases, two of which, pelL and pelZ, have been already identified. We cloned the pelI gene, encoding a ninth pectate lyase of E. chrysanthemi 3937. The pelI reading frame is 1,035 bases long, corresponding to a protein of 344 amino acids including a typical amino-terminal signal sequence of 19 amino acids. The purified mature PelI protein has an isoelectric point of about 9 and an apparent molecular mass of 34 kDa. PelI has a preference for partially methyl esterified pectin and presents an endo-cleaving activity with an alkaline pH optimum and an absolute requirement for Ca2+ ions. PelI is an extracellular protein secreted by the Out secretory pathway of E. chrysanthemi. The PelI protein is very active in the maceration of plant tissues. A pelI mutant displayed reduced pathogenicity on chicory leaves, but its virulence did not appear to be affected on potato tubers or Saintpaulia ionantha plants. The pelI gene constitutes an independent transcriptional unit. As shown for the other pel genes, the transcription of pelI is dependent on various environmental conditions. It is induced by pectic catabolic products and affected by growth phase, oxygen limitation, temperature, nitrogen starvation, and catabolite repression. Regulation of pelI expression appeared to be dependent on the three repressors of pectinase synthesis, KdgR, PecS, and PecT, and on the global activator of sugar catabolism, cyclic AMP receptor protein. A functional KdgR binding site was identified close to the putative pelI promoter. Analysis of the amino acid sequence of PelI revealed high homology with a pectate lyase from Erwinia carotovora subsp. carotovora (65% identity) and low homology with pectate lyases of the phytopathogenic fungus Nectria haematococca (Fusarium solani). This finding indicates that PelI belongs to pectate lyase class III. Using immunoblotting experiments, we detected PelI homologs in various strains of E. chrysanthemi and E. carotovora subsp. carotovora but not in E. carotovora subsp. atroseptica.
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PMID:Pectate lyase PelI of Erwinia chrysanthemi 3937 belongs to a new family. 939 96

RpoS (sigma-S or sigma-38) controls a large array of genes that are expressed during stationary phase and under various stress conditions in Escherichia coli and other bacteria. We document here that plant pathogenic and epiphytic Erwinia species, such as E. amylovora; E. carotovora subsp. atroseptica, betavasculorum, and carotovora; E. chrysanthemi; E. herbicola; E. rhapontici; and E. stewartii, possess rpoS genes and produce the alternate sigma factor. We show that rpoS transcription in E. carotovora subsp. carotovora is driven from a major promoter which resides within the nlpD gene located upstream of rpoS as in E. coli. RpoS- E. carotovora subsp. carotovoa strain AC5061, constructed by marker exchange, is more sensitive to hydrogen peroxide, carbon starvation, and acidic pH than its RpoS+ parent strain, AC5006. The basal levels of extracellular pectate lyase, polygalacturonase, and cellulase as well as those of transcripts of E. carotovora subsp. carotovora hrpN (hrpNEcc), the gene for the elicitor of the hypersensitive reaction, are higher in the RpoS- strain than in the RpoS+ parent. Likewise, compared to AC5006, AC5061 causes more extensive maceration of celery petioles. Our findings with the RpoS- mutant and strains carrying multiple copies rpoS+ DNA reveal that rpoS positively controls rsmA expression. We also present evidence that supports the hypothesis that the RpoS effect on extracellular enzyme levels, hrpNEcc expression, and virulence manifests itself by the modulation of rsmA expression.
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PMID:RpoS (sigma-S) controls expression of rsmA, a global regulator of secondary metabolites, harpin, and extracellular proteins in Erwinia carotovora. 965 7

Erwinia chrysanthemi 3937 secretes several pectinolytic enzymes, among which eight isoenzymes of pectate lyases with an endo-cleaving mode (PelA, PelB, PelC, PelD, PelE, PelI, PelL, and PelZ) have been identified. Two exo-cleaving enzymes, the exopolygalacturonate lyase, PelX, and an exo-poly-alpha-D-galacturonosidase, PehX, have been previously identified in other E. chrysanthemi strains. Using a genomic bank of a 3937 mutant with the major pel genes deleted, we cloned a pectinase gene identified as pelX, encoding the exopolygalacturonate lyase. The deduced amino acid sequence of the 3937 PelX is very similar to the PelX of another E. chrysanthemi strain, EC16, except in the 43 C-terminal amino acids. PelX also has homology to the endo-pectate lyase PelL of E. chrysanthemi but has a N-terminal extension of 324 residues. The transcription of pelX, analyzed by gene fusions, is dependent on several environmental conditions. It is induced by pectic catabolic products and affected by growth phase, oxygen limitation, nitrogen starvation, and catabolite repression. Regulation of pelX expression is dependent on the KdgR repressor, which controls almost all the steps of pectin catabolism, and on the global activator of sugar catabolism, cyclic AMP receptor protein. In contrast, PecS and PecT, two repressors of the transcription of most pectate lyase genes, are not involved in pelX expression. The pelX mutant displayed reduced pathogenicity on chicory leaves, but its virulence on potato tubers or Saintpaulia ionantha plants did not appear to be affected. The purified PelX protein has no maceration activity on plant tissues. Tetragalacturonate is the best substrate of PelX, but PelX also has good activity on longer oligomers. Therefore, the estimated number of binding subsites for PelX is 4, extending from subsites -2 to +2. PelX and PehX were shown to be localized in the periplasm of E. chrysanthemi 3937. PelX catalyzed the formation of unsaturated digalacturonates by attack from the reducing end of the substrate, while PehX released digalacturonates by attack from the nonreducing end of the substrate. Thus, the two types of exo-degrading enzymes appeared complementary in the degradation of pectic polymers, since they act on both extremities of the polymeric chain.
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PMID:Characterization of the exopolygalacturonate lyase PelX of Erwinia chrysanthemi 3937. 1004

Erwinia chrysanthemi 3937 secretes an arsenal of pectinolytic enzymes including several pectate lyases encoded by the pel genes. We characterized a novel cluster of pectinolytic genes consisting of the three adjacent genes pehV, pehW and pehX, whose products have polygalacturonase activity. The high similarity between the three genes suggests that they result from duplication of an ancestral gene. The transcription of pehV, pehW and pehX is dependent on several environmental conditions. They are induced by pectin catabolic products and this induction results from inactivation of the KdgR repressor which controls almost all the steps of pectin catabolism. The presence of calcium ions strongly reduced the transcription of the three peh genes. Their expression was also affected by growth phase, osmolarity, oxygen limitation and nitrogen starvation. In addition, the pehX transcription is affected by catabolite repression and controlled by the activator protein CRP. PecS, which was initially isolated as a repressor of virulence factors, acts as an activator of the peh transcription. We showed that the three regulators KdgR, PecS and CRP act by direct interaction with the promoter regions of the peh genes. Analysis of simultaneous binding of KdgR, PecS, CRP and RNA polymerase indicated that the activator effect of PecS results from a competition between PecS and KdgR for the occupation of overlapping binding sites. Thus, to activate peh transcription, PecS behaves as an anti-repressor against KdgR.
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PMID:Analysis of three clustered polygalacturonase genes in Erwinia chrysanthemi 3937 revealed an anti-repressor function for the PecS regulator. 1056 5

Erwinia chrysanthemi 3937 secretes an arsenal of pectinolytic enzymes, including at least eight endo-pectate lyases encoded by pel genes, which play a major role in the soft-rot disease caused by this bacterium on various plants. E. chrysanthemi also produces some hydrolases that cleave pectin. Three adjacent hydrolase genes, pehV, pehW, and pehX, encoding exo-poly-alpha-D-galacturonosidases, have been characterized. These enzymes liberate digalacturonides from the nonreducing end of pectin. We report the identification of a novel gene, named pehN, encoding a protein homologous to the glycosyl hydrolases of family 28, which includes mainly polygalacturonases. PehN has a low hydrolase activity on polygalacturonate and on various pectins. PehN action favors the activity of the secreted endo-pectate lyases, mainly PelB and PelC, and that of the periplasmic exo-pectate lyase PelX. However, removal of the pehN gene does not significantly alter the virulence of E. chrysanthemi. Regulation of pehN transcription was analyzed by using gene fusions. Like other pectinase genes, pehN transcription is dependent on several environmental conditions. It is induced by pectic catabolic products and is affected by growth phase, catabolite repression, osmolarity, anaerobiosis, nitrogen starvation, and the presence of calcium ions. The transcription of pehN is modulated by the repressor KdgR, which controls almost all the steps of pectin catabolism, and by cyclic AMP receptor protein (CRP), the global activator of sugar catabolism. The regulator PecS, which represses the transcription of the pel genes but activates that of pehV, pehW, and pehX, also activates transcription of pehN. The three regulators KdgR, PecS, and CRP act by direct interaction with the pehN promoter region. The sequences involved in the binding of these three regulators and of RNA polymerase have been precisely defined. Analysis of the simultaneous binding of these proteins indicates that CRP and RNA polymerase bind cooperatively and that the binding of KdgR could prevent pehN transcription. In contrast, the activator effect of PecS is not linked to competition with KdgR or to cooperation with CRP or RNA polymerase. This effect probably results from competition between PecS and an unidentified repressor involved in peh regulation.
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PMID:PehN, a polygalacturonase homologue with a low hydrolase activity, is coregulated with the other Erwinia chrysanthemi polygalacturonases. 1197 95

I examined the role of aerobic microbial populations in cellulose digestion by two sympatric species of desert millipedes, Orthoporus ornatus and Comanchelus sp. High numbers of bacteria able to grow on media containing cellulose, carboxymethyl cellulose, or cellobiose as the substrate were found in the alimentary tracts of the millipedes. Enzyme assays indicated that most cellulose and hemicellulose degradation occurred in the midgut, whereas the hindgut was an important site for pectin degradation. Hemicellulase and beta-glucosidase in both species and possibly C(x)-cellulase and pectinase in O. ornatus were of possible microbial origin. Degradation of [C]cellulose by millipedes whose gut floras were reduced by antibiotic treatment and starvation demonstrated a reduction in CO(2) release and C assimilation and an increase in C excretion over values for controls. It appears that the millipede-bacterium association is mutualistic and makes available to millipedes an otherwise mostly unutilizable substrate. Such an association may be an important pathway for decomposition in desert ecosystems.
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PMID:Role of aerobic microbial populations in cellulose digestion by desert millipedes. 1634 74

Production of carbohydrases by Alternaria solani is inhibited by glucose under low growth conditions. In an enriched medium, glucose has little effect on the production of polygalacturonase and cellulase while it still suppresses production of beta-glucosidase. Low levels of all three enzymes were produced in the absence of their respective substrates. Such regulation has been found with many organisms. However, far greater production of these carbohydrases occurred with additions of adenosine phosphates to the growth media. Highest stimulation of enzyme production was by adenosine 5'-phosphate. Adenosine 5'-triphosphate and cyclic 3', 5'-adenosine monophosphate gave lesser amounts. Starvation appears to induce production of extracellular carbohydrases and adenosine 5'-phosphate may have a role in the starvation process.
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PMID:Effect of Glucose and Adenosine Phosphates on Production of Extracellular Carbohydrases of Alternaria solani. 1665 49


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