Date of Award:

2015

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Advisor/Chair:

Jon Y. Takemoto

Abstract

Biliverdin IXα is a green bile pigment produced by enzymatic cleavage of a tetrapyrrole ring of heme by heme oxygenase. While biliverdin IXα is emerging as an effective cytoprotectant, the conventional method for producing biliverdin IXα by chemical conversion of animal bile is not suitable for large scale production. A novel scalable production method was pursued via bacterial fermentation. Recombinant Escherichia coli strains were obtained by sequence optimization and plasmid transformation of a cyanobacterial heme oxygenase gene. Further strain development was done by plasmid overexpression of a native E. coli flavodoxin gene as a possible electron donor for heterogeneous heme oxygenase. The resulting strains were grown in a fed-batch culture system optimized for biliverdin IXα production.

Syringomycin E is a lipodepsinonapeptide produced by certain strains of Pseudomonas syringae pv. syringae by nonribosomal peptide synthesis. Though syringomycin E had been considered a phytotoxin in the past, recent research results indicate that syringomycin E is a natural fungicide that is not toxic to animals and plants. Syringomycin E is a potential fungicide especially for use in the organic agriculture sector. New strains of P. syringae pv. syringae were isolated through ultraviolet mutagenesis and screenings for enhanced capability to produce syringomycin E especially under agitated conditions. Fermentative production was conducted in a newly formulated medium and the product was purified through a large scale chromatography system using organic-compatible solvents. Purified syringomycin E was tested on cucumber seeds to examine its antifungal activity against a soil-borne pathogen Pythium ultimum. Syringomycin E was able to inhibit Pythium infection and protected seeds and seedlings without developing disease symptoms.

This dissertation research showed scalable production of two natural products, biliverdin IXα and syringomycin E in bacterial platforms. Strain development by gene recombination and mutation was done to obtain bacterial strains capable of overproducing desired metabolites. The resulting strains were grown in fermenters to maximize the yields under agitated conditions. Monitoring growth parameters and medium modifications were critical to achieve large scale production.

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Biology Commons

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