Thesis
The potential role of biofilm in the pathogenicity of Enterobacter cloacae, causal agent of Enterobacter onion bulb decay
Washington State University
Master of Science (MS), Washington State University
2011
Handle:
https://hdl.handle.net/2376/102557
Abstract
Washington State is the third largest producer of storage onions, with a farm-gate value of greater than $100 million. A current problem in Washington onion bulb production is Enterobacter bulb decay, which is caused by the bacterium Enterobacter cloacae. This postharvest disease produces a discoloration of one or two inner scales of onion bulbs in storage with no tissue maceration, odor, or symptoms. In order to identify genes that have a role in the E. cloacae-onion interaction, a mini-Tn5 mutagenesis library of E. cloacae strain EcWSU1R was screened on Luria Bertani agar amended with congo red (CR) to identify polysaccharide mutants. Forty-six unique CR mutants were assayed for solid-surface-associated biofilm production by using a crystal violet staining assay. Twenty-two CR mutants produced a solid-surfaceassociated biofilm that was significantly less than the rifampicin-resistant strain EcWSU1R (P< 0.0001). Using whole-bulb assays, it was determined that the CR mutants were not reduced in ability to cause onion bulb rot compared to ECWSU1R (P=0.2395). E. cloacae strains EcWSU1R, CR42, and CR78 (a rifampicin-resistant strain, a biofilm underproducer and an overproducer, respectively) were inoculated into the leaves of 17-week-old onion plants to determine movement dynamics in planta. All three strains moved bidirectionally through the leaves and were detected 0.5 – 2 cm from the point of inoculation in the first 2 weeks and 14 – 26 cm from the point of inoculation in the third through sixth weeks. Populations of all three strains increased in planta from 106 CFU plant-1 initially to 108 CFU plant-1 after six weeks. Scanning electron microscopy (SEM) was used to visualize EcWSU1R, CR42 and CR78 in onion leaves in an attempt to determine which tissues were colonized by the bacteria. Bacterial cells were not observed in any tissues; however, a matrix was present in the phloem of onion leaves inoculated with strains EcWSU1R, CR42 and CR78, which was not present in waterinoculated tissues. This research increased our understanding of the E. cloacae-onion interaction to assist in developing management strategies that reduce Enterobacter bulb decay of onion.
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Details
- Title
- The potential role of biofilm in the pathogenicity of Enterobacter cloacae, causal agent of Enterobacter onion bulb decay
- Creators
- Sarah Michelle Dossey
- Contributors
- Brenda K. Schroeder (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Plant Pathology, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525032701842
- Language
- English
- Resource Type
- Thesis