RESUMO
One of the most economically important bacterial pathogens of plants and plant products is
Assuntos
Bacteriófagos/isolamento & purificação , Agentes de Controle Biológico/isolamento & purificação , Dickeya chrysanthemi/crescimento & desenvolvimento , Dickeya chrysanthemi/virologia , Doenças das Plantas/microbiologia , Solanum tuberosum/microbiologia , Sequência de Bases , Bacteriófagos/classificação , Agentes de Controle Biológico/classificação , DNA Bacteriano/genética , Testes de Sensibilidade Microbiana , Dados de Sequência Molecular , Myoviridae/classificação , Myoviridae/isolamento & purificação , Dickeya chrysanthemi/efeitos dos fármacos , Dickeya chrysanthemi/isolamento & purificação , /genética , Análise de Sequência de DNA , Siphoviridae/classificação , Siphoviridae/isolamento & purificaçãoRESUMO
Siderophores (ferric ion chelators) are secreted by organisms in response to iron deficiency. The pathogenic enterobacterium Erwinia chrysanthemi produces two siderophores, achromobactin and chrysobactin (CB), which are required for systemic dissemination in host plants. Previous studies have shown that CB is produced in planta and can trigger the up-regulation of the plant ferritin gene AtFER1. To further investigate the function of CB during pathogenesis, we analyzed its effect in Arabidopsis (Arabidopsis thaliana) plants following leaf infiltration. CB activates the salicylic acid (SA)-mediated signaling pathway, while the CB ferric complex is ineffective, suggesting that the elicitor activity of this siderophore is due to its iron-binding property. We confirmed this hypothesis by testing the effect of siderophores structurally unrelated to CB, including deferrioxamine. There was no activation of SA-dependent defense in plants grown under iron deficiency before CB treatment. Transcriptional analysis of the genes encoding the root ferrous ion transporter and ferric chelate reductase, and determination of the activity of this enzyme in response to CB or deferrioxamine, showed that these compounds induce a leaf-to-root iron deficiency signal. This root response as well as ferritin gene up-regulation in the leaf were not compromised in a SA-deficient mutant line. Using the Arabidopsis-E. chrysanthemi pathosystem, we have shown that CB promotes bacterial growth in planta and can modulate plant defenses through an antagonistic mechanism between SA and jasmonic acid signaling cascades. Collectively, these data reveal a new link between two processes mediated by SA and iron in response to microbial siderophores.
Assuntos
Arabidopsis/imunologia , Arabidopsis/microbiologia , Dickeya chrysanthemi/metabolismo , Fenômenos do Sistema Imunitário/efeitos dos fármacos , Ferro/metabolismo , Sideróforos/farmacologia , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de Transporte de Cátions/genética , Proteínas de Transporte de Cátions/metabolismo , Dickeya chrysanthemi/efeitos dos fármacos , Dickeya chrysanthemi/crescimento & desenvolvimento , Dipeptídeos/farmacologia , Etilenos/metabolismo , FMN Redutase/genética , FMN Redutase/metabolismo , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genes de Plantas , Quelantes de Ferro/farmacologia , Modelos Biológicos , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/microbiologia , Ácido Salicílico/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Regulação para Cima/efeitos dos fármacosRESUMO
Erwinia chrysanthemi is a phytopathogenic soil enterobacterium closely related to Escherichia coli. Both species respond to hyperosmotic pressure and to external added osmoprotectants in a similar way. Unexpectedly, the pools of endogenous osmolytes show different compositions. Instead of the commonly accumulated glutamate and trehalose, E. chrysanthemi strain 3937 promotes the accumulation of glutamine and alpha-glucosylglycerate, which is a new osmolyte for enterobacteria, together with glutamine. The amounts of the three osmolytes increased with medium osmolarity and were reduced when betaine was provided in the growth medium. Both glutamine and glutamate showed a high rate of turnover, whereas glucosylglycerate stayed stable. In addition, the balance between the osmolytes depended on the osmolality of the medium. Glucosylglycerate and glutamate were the major intracellular compounds in low salt concentrations, whereas glutamine predominated at higher concentrations. Interestingly, the ammonium content of the medium also influenced the pool of osmolytes. During bacterial growth with 1 mM ammonium in stressing conditions, more glucosylglycerate accumulated by far than the other organic solutes. Glucosylglycerate synthesis has been described in some halophilic archaea and bacteria but not as a dominant osmolyte, and its role as an osmolyte in Erwinia chrysanthemi 3937 shows that nonhalophilic bacteria can also use ionic osmolytes.
Assuntos
Dickeya chrysanthemi/fisiologia , Glutamatos/metabolismo , Glutamina/metabolismo , Glicolipídeos/metabolismo , Equilíbrio Hidroeletrolítico , Betaína/metabolismo , Meios de Cultura , Dickeya chrysanthemi/crescimento & desenvolvimento , Dickeya chrysanthemi/metabolismo , Concentração Osmolar , Pressão OsmóticaRESUMO
Cellular components necessary for osmoprotection are poorly known. In this study we show that O antigen is specifically required for the effectiveness of betaines as osmoprotectants for Erwinia chrysanthemi in saline media. The phenotype is correlated with the inability of rfb mutant strains to maintain a high accumulation level of betaines in hypersaline media.
Assuntos
Betaína/metabolismo , Dickeya chrysanthemi/química , Dickeya chrysanthemi/fisiologia , Antígenos O/fisiologia , Proteínas de Bactérias/genética , Proteínas de Bactérias/fisiologia , Meios de Cultura/química , Elementos de DNA Transponíveis , Dickeya chrysanthemi/crescimento & desenvolvimento , Genes Bacterianos , Família Multigênica , Mutagênese Insercional , Mutação , Concentração Osmolar , Solução Salina HipertônicaRESUMO
The plant pathogen Erwinia chrysanthemi produces a variety of factors that have been implicated in its ability to cause soft-rot diseases in various hosts. These include HrpN, a harpin secreted by the Hrp type III secretion system; PelE, one of several major pectate lyase isozymes secreted by the type II system; and PelL, one of several secondary Pels secreted by the type II system. We investigated these factors in E. chrysanthemi EC16 with respect to the effects of medium composition and growth phase on gene expression (as determined with uidA fusions and Northern analyses) and effects on virulence. pelE was induced by polygalacturonic acid, but pelL was not, and hrpN was expressed unexpectedly in nutrient-rich King's medium B and in minimal salts medium at neutral pH. In contrast, the effect of medium composition on hrp expression in E. chrysanthemi CUCPB1237 and 3937 was like that of many other phytopathogenic bacteria in being repressed in complex media and induced in acidic pH minimal medium. Northern blot analysis of hrpN and hrpL expression by the wild-type and hrpL::omegaCmr and hrpS::omegaCmr mutants revealed that hrpN expression was dependent on the HrpL alternative sigma factor, whose expression, in turn, was dependent on the HrpS putative sigma54 enhancer binding protein. The expression of pelE and hrpN increased strongly in late logarithmic growth phase. To test the possible role of quorum sensing in this expression pattern, the expI/expR locus was cloned in Escherichia coli on the basis of its ability to direct production of acyl-homoserine lactone and then used to construct expI mutations in pelE::uidA, pelL::uidA, and hrpN::uidA Erwinia chrysanthemi strains. Mutation of expI had no apparent effect on the growth-phase-dependent expression of hrpN and pelE, or on the virulence of E. chrysanthemi in witloof chicory leaves. Overexpression of hrpN in E. chrysanthemi resulted in approximately 50% reduction of lesion size on chicory leaves without an effect on infection initiation.
Assuntos
Dickeya chrysanthemi/genética , Polissacarídeo-Liases/genética , Northern Blotting , Clonagem Molecular , Dickeya chrysanthemi/enzimologia , Dickeya chrysanthemi/crescimento & desenvolvimento , Dickeya chrysanthemi/patogenicidade , Regulação Bacteriana da Expressão Gênica , Isoenzimas/genética , Dados de Sequência Molecular , Mutagênese , Doenças das Plantas/microbiologia , Folhas de Planta/microbiologia , Nicotiana/microbiologia , Transcrição Gênica , VirulênciaRESUMO
Whole cells of the phytopathogenic Erwinia chrysanthemi strains were immobilized in k-carrageenan and grown in high-calcium Xanthomonas campestris medium containing sodium polypectate as carbon source. All the strains used survived immobilization into k-carrageenan beads. Immobilized E. chrysanthemi strains displayed higher pectolytic and proteolytic enzyme activities than free cells in liquid suspension. Carrageenan immobilization techniques could provide a system to mimic the conditions of E. chrysanthemi cells in the infected plant tissue. This could prompt a thorough study of the factors governing the biosynthesis of virulence factors by this bacterium.