PNNL-13501 - Pacific Northwest National Laboratory

Fungal Conversion of Waste Glucose/Cellulose Materials: Organic Solvents/Organic Acids
Study Control Number: PN00048/1455
Susan A. Thomas, Margaret R. Pinza, Peter Becker
Agricultural wastes such as corn fiber or other cellulose- or glucose-containing material into useful and marketable
products. Examples include 3- to 6-carbon chain length organic acids and solvents that can be used as industrial chemical
precursors.
Project Description
The experimental design included screening 46 fungal
strains for chemical byproduction on processed corn
glucose material in liquid culture. Specifically, the liquid
exudates were analyzed by liquid chromatography for the
presence and relative quantities of organic alcohols and
acids. Approximately 20 strains were selected as
candidates for further study based on the production of
some organic acids or alcohols and for growth on a 10%
glucose medium.
Background
The current use for corn glucose waste is conversion to
low-value animal feed, which is sold at or near cost to
European markets. The use of fungus and their enzymes
to convert spent corn glucose waste into useful organic
acids and solvents has the advantages of providing valueadded
domestic products and high-protein residue for
animal feed and reducing transportation costs and energy
use for production.
Introduction
The goal of this study was to prove the concept that
higher filamentous fungi can be used to produce desirable
organic acids and solvents in liquid fermentation with
processed corn glucose. Fungal biotechnology is the
application of fungi or their subcellular components in the
context of associated process-technology for
manufacturing service industries and for environmental
management (Arora et al. 1992). Typically, fungi are
employed to produce biomass, to produce or to catalyze
the production of useful end products, or to degrade
biological and chemical wastes and contaminants.
We have a patent pending on the method of
preconditioning fungal strains to contaminants of interest
and then using the preconditioned strains to remove or
degrade contaminants. This method results in proprietary
strains that are specifically adapted to more efficiently
remediate contaminants of interest under prescribed
environmental conditions. Our mycoremediation study
began in 1996, and since that time a variety of
contaminants have been addressed: organophosphates,
petroleum hydrocarbons, endocrine disrupters, pesticides,
fertilizers, alkaloids, and several strains of bacteria. We
expect that if preconditioned strains of fungus are used to
degrade processed corn glucose, then greater quantities of
acids or solvents could be produced.
Current industry practices use bacterial systems to
perform the conversion of glucose waste to lactic acid.
This practice is limited in the ability to convert
commercial quantities both at a competitive cost and
without generating a waste stream (T Werpy, Pacific
Northwest National Laboratory, personal communication,
September 1999). The advantage of filamentous fungi for
the byproduction of organic acids and solvents is the
efficiency and low cost of the method. For example, use
of the fungal systems should eliminate certain steps
required in the bacterial approach because of the tolerance
of low pH and high salinity of the fungal strains we use.
The bacterial approach requires neutralization of the
fermentation process with compounds such as calcium
hydroxide, the subsequent recovery of the desired product
(lactic acid) by addition of gypsum or similar compounds,
and the consequent need to treat the waste streams
generated by these steps.
Approach
We screened a total of 46 species. The cultures were all
grown initially on Difco malt extract agar, and were then
converted to malt extract broth culture by homogenizing
the malt extract agar plates with 50 mL to 100 mL sterile
malt extract broth and decanting the homogenate into
sterile 500-mL Erlenmeyer fermentation flasks with
bubbler tubes and vented stoppers containing 250 mL to
400 mL sterile malt extract broth. Filtered air from the
laminar flow hood was supplied to stir the flask contents
by bubbling the air from near the bottom of the flask
through a cotton-plugged, sterile 1-mL pipette (Figure 1).
Biosciences and Biotechnology 73