Jason Jerke

Document Type

Thesis - University Access Only

Award Date

2001

Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology

First Advisor

William Gibbons

Abstract

Aureobasidium pu/lulans is a polymorphic fungus that produces the exopolysaccharide pullulan. Pullulan is currently manufactured to a limited extent, but has many characteristics suitable for uses in the food, pharmaceutical, manufacturing and plastic industries. A. pullulans has a complex life cycle and requires specific environmental and nutritional factors to produce pullulan. In addition, the fungus requires a high concentration of carbohydrates to produce acceptable levels of pullulan, making medium costs very expensive. The overall objective ofthis project was to grow A. pu/lulans in a medium based on a low-value by-product from fuel ethanol plants (condensed com solubles) and produce pullulan at concentrations comparable to those derived from the traditional medium, Ueda. To accomplish this objective, I evaluated wet-mill condensed com distiller's solubles (CCDS) as a low-cost alternative medium. Wild type (ATCC 42023) and overproducing (DG-1) strains of A. pullulans were acclimated to grow on CCDS, but growth was slow and pullulan production was minimal. After a series of shake flasks trials, it was decided that CCDS contained some component that inhibited both biomass and pullulan production. The acclimated strain, DG-1 A 1, was then successfully cultured on dry-mill CCS without further acclimation. V A series of shake flask trials was completed on Ueda verses various formulations of CCS-based media with strains DG-1 A 1. Ueda proved to be the best medium producing pullulan concentrations of23.3 g/L with a viable cell count of 5.60 x 107 CFU/ml. The best CCS-based medium was WBG 100 g/L sucrose, producing a pullulan concentration of 10.1 g/L with a viable count of 1.34 x 10 8 CFU/ml. Fermentor trials followed, with similar relationships occurring between media types as in the shake flask trials. As expected, however, both biomass and pullulan concentrations rose significantly, as aeration and agitation rates could be more optimally maintained. In these trials, a maximum pullulan concentration of 64.2 g/L (Ueda) and 24.5 g/L (CCS 100 g/L sucrose) were obtained, with correspondingly higher cell populations, pullulan productivities, and pullulan yields. These results were significantly better than those reported in the literature and likely reflect the combination of an overproducing strain, high sucrose levels and optimized aeration and agitation rates. These results show that CCS has a complex nutritional content, which proved suitable for growth and pullulan production, without the additional expensive defined media components comprising Ueda.

Library of Congress Subject Headings

Polysaccharides -- Synthesis Pleomorphic fungi Corn products industry -- By-products

Publisher

South Dakota State University

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Rights Statement

In Copyright