The U.S. Air Force
Material Science directorate has identified the compounds
m-hydroxybiphenyl (m-HBP) and m-hydroxydiphenylacetylene (m-HDPA) as
critical precursors in the production of high performance
polymers. Epoxy resins synthesized using m-HBP or m-HDPA have
exceptional thermal resistance and could be used in a number of
important aerospace applications. While m-HBP and m-HDPA are difficult
to produce by normal chemical synthesis, biocatalysis may offer an
alternative method. Research by Dr. Glenn Johnson at Tyndall AFB,
FL has identified two bacterial enzymes that are capable of producing
either m-HBP from biphenyl or m-HDPA from diphenyl acetylene (DPA).In
these studies, product purities as high as 90% were observed.
Unfortunately, the reaction rates were quite low, due in part to the
low aqueous solubility of biphenyl and DPA. Chemical reaction rates are
generally proportional to the concentration of reactant in
solution.
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Fed-batch
operation of a bioreactor to grow recombinant E. coli
expressing a foreign gene
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Bioreactor,
control unit & computer control station used in biochemical
engineering lab.
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To increase
biocatalysis rates for these compounds, the effective concentration of
enzyme and/or substrate in solution must be increased. While Dr.
Johnson has developed an E. coli strain that will over express
the genes that encode for our desired enzymes, the culture environment
can have a significant effect on the actual amount of enzyme produced. Jason Herr
is currently evaluating fed-batch strategies
for the production of high cell density E. coli cultures.By increasing
the cell density prior to induction,we hope to maximize the overall
enzyme concentration in solution. Conversely, Sowmya Talari is trying to increase the effective substrate
concentration in aqueous solution through the addition of
surfactants. Certain surfactants are toxic to specific bacterial
species; thus, we are screening a variety of surfactant compounds to
determine the optimal one for our particular biocatalysis system.
High Performance Liquid
Chromatography (HPLC) is used extensively in our research for the
quantification of various compounds in our fermentations.
This research is supported by the Air Force
Research Laboratory through the
DoD-EPSCoR program