Date of Award

5-6-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

George Pierce

Second Advisor

Eric Gilbert

Third Advisor

Sidney Crow

Abstract

Rhodococcus rhodochrous is a ubiquitous soil bacterium that has long been employed in industry for its diverse metabolism. It has been used to convert acrylonitrile to acrylamide using urea and cobalt as inducers. Pierce et al. demonstrated that using induction conditions and propagation this microbe produces gasses that can delay the ripening in climacteric fruit as well as inhibiting the growth of post-harvest spoilage microbes on the fruits.

The relationship between R. rhodochrous DAP 96253, harvested fruits, and their pathogens was examined. Whole-cell immobilization was used to prolong the activity of the rhodococci, and a cold storage study was conducted using strawberries. An edible wax emulsion was found to most effectively inhibit the growth of fungi on fruits without contact. It was particularly effective in reducing the growth of fast-growing Rhizopus and Mucor spp. The volatile profile of R. rhodochrous DAP 96253 grown under different conditions was compared as were strawberries treated with different formulations of rhodococcal catalyst. The efficacy of pure VOCs previously found to be antifungal were tried against grain contaminant Aspergillus flavus and compared to induced R. rhodochrous. Of those tested benzaldehyde and 1-ethyl 2-hexanol were found to be the most effective against spores.

Recently, this bacterium was shown to produce asparaginase and studies were conducted to increase enzyme titer in the growing cells. Bacterially-derived asparaginase is used to treat acute lymphoblastic leukemia. The enzyme is used to deplete asparagine in cancer cells which ultimately causes apoptosis. While commercial treatments are effective, the side effects and high cost are hurdles in the treatment process. This study sought to produce high levels of asparaginase in R. rhodochrous DAP 96253 at pre-pilot production scale with controllable levels of glutaminase.

Available for download on Thursday, April 22, 2021

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