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(1 - 8 of 8)
- Title
- A microbiological study of Erwinia amylovora exopolysaccharide ooze
- Creator
- Slack, Suzanne Marie
- Date
- 2016
- Collection
- Electronic Theses & Dissertations
- Description
-
Fire blight, caused by the pathogen Erwinia amylovora (Burrill) Winslow et al, is the most devastating bacterial disease of pome fruits around the world. The primary dispersal of E. amylovora is through ooze, a mass of exopolysaccharides and bacterial cells that is exuded from infected host tissue. Over the 2013 and 2014 field seasons, 631 ooze droplets (201 in 2013 and 435 in 2014) were collected from field inoculated trees. Populations of E. amylovora in ooze droplets range from 108 to 1011...
Show moreFire blight, caused by the pathogen Erwinia amylovora (Burrill) Winslow et al, is the most devastating bacterial disease of pome fruits around the world. The primary dispersal of E. amylovora is through ooze, a mass of exopolysaccharides and bacterial cells that is exuded from infected host tissue. Over the 2013 and 2014 field seasons, 631 ooze droplets (201 in 2013 and 435 in 2014) were collected from field inoculated trees. Populations of E. amylovora in ooze droplets range from 108 to 1011 colony forming units per micro liter (cfu/μl). In the host tissue surrounding the droplets even larger populations of E. amylovora reside in the surrounding 1 cm of tissue. Three apple cultivars with varying levels of resistance were also infected with four Michigan E. amylovora strains. Using scanning electron microscopy, host tissue was examined for the origin of the ooze droplets and erumpent mounds and small (10 μm) tears were the only bacterial sources observed. Genetic expression analysis indicated that E. amylovora cells in stem sections located above ooze drops and in ooze drops were actively expressing virulence genes. If disseminated to susceptible host tissue, these cells would be primed for infection. The current study suggests the following: high populations of E. amylovora are present in ooze droplets which larger populations found in darker pigmented, smaller volume droplets. These droplets are rupturing out from the parenchyma and epidermis of the host, with evidence of immense pressure being involved from SEM observations. Ooze droplet volume and population can vary between host cultivar and the virulence of a specific E. amylovora strain. Genetic expression analysis of virulent factors in E. amylovora indicated that the bacteria in ooze were primed and ready to infect a new susceptible host.
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- Title
- Cyclic di-GMP regulates EPS secretion, biofilm formation, and motility in the plant pathogen Erwinia amylovora
- Creator
- Edmunds, Adam Christopher
- Date
- 2011
- Collection
- Electronic Theses & Dissertations
- Description
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The second messenger cyclic di-GMP (c-di-GMP) is a nearly ubiquitous intracellular signal molecule known to regulate various cellular processes including biofilm formation, motility, and virulence. This intracellular concentration of this molecule is inversely governed by GGDEF-containing proteins (GCPs) and EAL-containing proteins (ECPs), which synthesize and degrade c-di-GMP, respectively. The role of this regulatory molecule in the plant pathogen and causal agent of fire blight disease, ...
Show moreThe second messenger cyclic di-GMP (c-di-GMP) is a nearly ubiquitous intracellular signal molecule known to regulate various cellular processes including biofilm formation, motility, and virulence. This intracellular concentration of this molecule is inversely governed by GGDEF-containing proteins (GCPs) and EAL-containing proteins (ECPs), which synthesize and degrade c-di-GMP, respectively. The role of this regulatory molecule in the plant pathogen and causal agent of fire blight disease,Erwinia amylovora was explored. In this study, it is demonstrated that E. amylovora contains three functional diguanylate cyclases (DGCs) that synthesize c-di-GMP: gcp1 , gcp3 , and gcp5 ; and two functional c-di-GMP specific phosophodiesterases (PDEs) that degrade c-di-GMP: ecp1 and ecp3 . C-di-GMP was not detected in the wild type strain. C-di-GMP was shown to positively regulate biofilm formation and secretion of the main expolysaccharide amylovoran and to inversely regulate swimming motility and virulence. A deletion of ecp3 resulted in a hyper-biofilm forming phenotype. Interestingly, over-expression of dgc1, which contains both an EAL and a GGDEF domain, resulted in no observable phenotypic differences from the wild type strain, even though over-expression of dgc1 increased the levels of c-di-GMP.
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- Title
- The role of biofilm formation in systemic movement of Erwinia amylovora in apple
- Creator
- Koczan, Jessica
- Date
- 2011
- Collection
- Electronic Theses & Dissertations
- Description
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Erwinia amylovora is a highly virulent, necrogenic plant pathogen that causes fire blight disease on apple, pear, and other rosaceous plants. The fire blight pathogen is highly invasive and capable of rapid systemic movement through plants. Current methods of control focus on chemical and antibiotic treatments. The popularity of highly susceptible cultivars and the emergence of antibiotic resistance have driven the need to find other methods to control fire...
Show moreErwinia amylovora is a highly virulent, necrogenic plant pathogen that causes fire blight disease on apple, pear, and other rosaceous plants. The fire blight pathogen is highly invasive and capable of rapid systemic movement through plants. Current methods of control focus on chemical and antibiotic treatments. The popularity of highly susceptible cultivars and the emergence of antibiotic resistance have driven the need to find other methods to control fire blight. The study of pathogen virulence factors has the potential to identify novel control methods. Several bacterial virulence factors have been shown to be critical for biofilm formation, the production in a complex aggregated network of bacterial cells, exopolysaccharides, and other macromolecules. In addition, vascular plant pathogens commonly use the ability of biofilm formation to aid in the systemic movement of the pathogen. Research presented here used in silico analysis to identify several virulence factors. Biofilm formation and virulence assays determined that virulence factors that contribute to the systemic movement ofE .amylovora in vascular tissue of apple. The production of exopolysaccharides amylovoran and levan was determined to be needed for the formation of a mature biofilm. Though cells are motile, amylovoran deficient mutants are unable to move past the site of inoculation. Levan deficient mutants display a delayed, reduced virulence phenotype. Several putative bacterial surface proteins, or attachment structures, assist in the initial attachment (both reversible and irreversible) of the pathogen to host tissue. Deletions in genes encoding for the production of attachment structures drastically reduce the biofilm capability ofE .amylovora , and the ability to get into the xylem tissue. In addition, mutation of functional flagellar motor stators demonstrated that motility was important in mediating contact of bacterial cells to surfaces. Motility of the fire blight pathogen is shown to be important in the movement of bacterial cells within host tissue. Additionally, motility seems to be important in the expansion of biofilms. In total, the contribution of the virulence factors to biofilm formation and the localization of the pathogen in host tissue imply that biofilm formation assists in the systemic movement ofE .amylovora in apple.
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- Title
- Disease management in apples using trunk injection delivery of plant protective compounds
- Creator
- Acimovic, Srdan Goran
- Date
- 2014
- Collection
- Electronic Theses & Dissertations
- Description
-
The two most important pathogens of apple Erwinia amylovora (fire blight) and Venturia inaequalis (apple scab) require pesticide sprays for control. This leads to accumulating side effects such as disease resistance, contamination of environment, elevated fungicide residues in fruit, and increased health risks to consumers and workers. While sprays are effective for disease control, need for increasing the sustainability of apple production by reducing pesticide use in the environment incited...
Show moreThe two most important pathogens of apple Erwinia amylovora (fire blight) and Venturia inaequalis (apple scab) require pesticide sprays for control. This leads to accumulating side effects such as disease resistance, contamination of environment, elevated fungicide residues in fruit, and increased health risks to consumers and workers. While sprays are effective for disease control, need for increasing the sustainability of apple production by reducing pesticide use in the environment incited our research on delivering pesticides via trunk injection. This method delivers the compound into the canopy via tree xylem and could increase the efficiency in disease control. To find out how, where and when injected compounds distribute in the apple tree, thus affecting the efficiency in pest control, we injected imidacloprid through 1, 2, 4, or 8 injection ports per tree. By quantifying leaf residues we demonstrated variable spatial distribution of imidacloprid in the canopy. Spatial uniformity of distribution increased with more injection ports and 4 ports provided uniform distribution. To demonstrate the efficiency of injected compounds in fire blight and apple scab control we injected apple trees with antibiotics, plant resistance inducers, and fungicides. Antibiotics, potassium phosphites (PJ) and acibenzolar-S-methyl (ASM) provided weak control of blossom and shoot blight while oxytetracycline was the most efficient. ASM and PJ significantly expressed PR-1, 2, and 8 protein genes showing resistance activation in apple leaves (SAR) which suppressed the pathogen. Four injections of PJ in spring controlled leaf apple scab for 2 seasons, similar to 2 seasons of standard sprays. To optimize injections for apple scab control we evaluated 1-2 and 4 cross-seasonal and 1-2 seasonal injections of PJ and fungicides. PJ provided better scab control than propiconazole, cyprodinil and difenoconazole and showed better or equal and more persistent scab control with fewer injections than sprays. Control varied among canopy organs due to different transpiration, with best scab control on shoots, fruit, and then spurs. Good scab control is provided by 2-3 spring injections. Residues of synthetic fungicides in fruit were always below the residue tolerances. Fall injection did not improve apple scab control. To get temporally uniform imidacloprid distribution in the crown, best results were achieved by injection dose delivery at 4 times, 14 days apart. Injection method comparison showed that drill-based injection of the liquid imidacloprid formulation provided the highest residue concentration in the canopy when compared to other injection methods. Comparison of 7 trunk injection devices showed that drill-based devices did not provide higher residue concentration of cyprodinil and difenoconazole in apple leaf canopy when compared to needle-insertion device Bite, while Wedgle was similar. All the injection devices allowed similar apple scab control with fungicides. When monitoring the rate of trunk injection port healing in apple trees, we found that port closure with callus lasted for 1-1.3 and >2 years depending on the port size and type. Port closure was faster on the ports with smaller diameters. Around all injection port types, bark cracking due to frost events was higher in vertical direction of the trunk. The visible port depth declined faster on port from 11/64" drill bit and on lenticular injection port from double-edge blade, versus the port from 3/8" drill bit. When the port from 3/8" drill bit was sealed with an Arborplug, visible and covered port depths significantly increased in time due to callus formation on the top and laterally, around the plug. Overall, trunk injection of injection formulated pesticides could be a viable option for disease control in apples with minimal impact of injection ports on the tree.
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- Title
- Ecological and genetic analysis of streptomycin-resistant Erwinia amylovora in Michigan and epidemiology of fire blight in an apple nursery
- Creator
- McManus, Patricia S.
- Date
- 1994
- Collection
- Electronic Theses & Dissertations
- Title
- Bacteriophages of Eriwinia amylovora : their isolation, distribution, characterization, and possible involvement in the etiology and epidemiology of fire blight
- Creator
- Ritchie, David Frey
- Date
- 1978
- Collection
- Electronic Theses & Dissertations
- Title
- Identification and analysis of induced genes from Erwinia amylovora and Malus x domestica during fire blight infection
- Creator
- Blumer-Schuette, Sara E.
- Date
- 2006
- Collection
- Electronic Theses & Dissertations
- Title
- Investigating carbohydrate utilization and virulence in Erwinia amylovora
- Creator
- Sweeney, Emma M.
- Date
- 2018
- Collection
- Electronic Theses & Dissertations
- Description
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Fire blight, caused by the gram-negative bacterium Erwinia amylovora, is a destructive disease of apple and pear trees worldwide. A unique aspect of apple and pear physiology is the presence of sorbitol in the leaves and shoots, glucose on the flower stigma surface and sucrose in the flower nectary. Erwinia amylovora cells encounter all three carbohydrates at different stages of infection, and it is unknown how the carbohydrate utilization genes are regulated between these changing nutrient...
Show moreFire blight, caused by the gram-negative bacterium Erwinia amylovora, is a destructive disease of apple and pear trees worldwide. A unique aspect of apple and pear physiology is the presence of sorbitol in the leaves and shoots, glucose on the flower stigma surface and sucrose in the flower nectary. Erwinia amylovora cells encounter all three carbohydrates at different stages of infection, and it is unknown how the carbohydrate utilization genes are regulated between these changing nutrient environments. This thesis explores carbohydrate utilization by E. amylovora in relation to virulence, regulatory small RNAs (sRNAs), other virulence factors and host specificity. The findings presented here indicate that sorbitol utilization (srl) gene mutants of E. amylovora are amylovoran-deficient, and they are unable to obtain the energy base needed to infect apple shoots and immature pear fruits. Additionally, the sRNA Spot 42 does not regulate sorbitol as it does in Escherichia coli, and we hypothesize that E. amylovora has evolved to evade Spot 42 regulation in order to adapt to the high-sorbitol content of apple and pear hosts.
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