Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing organic compound
Reexamination Certificate
2001-02-26
2002-12-17
Wong, Edna (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing organic compound
C205S440000, C205S450000
Reexamination Certificate
active
06495023
ABSTRACT:
BACKGROUND OF THE INVENTION
Microbial fermentation and biotransformation reactions are being employed with increasing frequency in the production of a number of commercially and industrially important products. There is also growing interest in developing alternative energy sources through microbial fermentation of waste materials. The economic feasibility of these processes depends on maximizing the efficiency of the fermentation or biotransformation reactions.
Bacterial species are able to use various energy sources, including light and diverse organic and inorganic chemicals, for growth and metabolism. These energy sources are used to produce an electrochemical gradient that provides an electron donor for metabolism and allows maintenance of a membrane potential and proton motive force. The energetics of living systems are driven by electron transfer processes in which electrons are transferred from a substrate, which is thereby oxidized, to a final electron acceptor, which is thereby reduced.
In microbial metabolism, the energy produced from the driving force of electrons is directly proportional to the potential energy difference (&Dgr;E
0
′) between the initial electron donor (the first biochemical dehydrogenating reaction) and final electron acceptor (e.g., the final biochemical hydrogenating reaction).
Certain microorganisms (e.g., Escherichia and Actinobacillus) are able to grow using H
2
as an electron donor to reduce fumarate into succinate in an anaerobic respiration process. These bacteria obtain free energy and reducing power from the electron driving force generated by the E
0
′ difference between the coupled oxidoreduction half reactions of [2H
+
/H
2
] and [fumarate/succinate].
Methanogens are strict anaerobic archea that can couple H
2
or HCOOH oxidation to CO
2
reduction into methane. Methanogenesis produces less free energy than other anaerobic respiration processes (e.g., fumarate, nitrate, or sulfate reduction) because the E
0
′ difference between the half oxidation reduction reactions of [2H
+
/H
2
] and [CO
2
/CH
4
] is relatively small.
Hydrogen oxidation by microbial hydrogenases can be coupled to reduction of various biological electron carriers including NAD
+
, cytochromes, and quinones or to certain artificial redox dyes, such as methyl-viologen and neutral red (NR) (Annous, et al., 1996
, Appl. Microbiol. Biotechnol
. 45:804-810, Kim, et al., 1992
, J. Microbiol. Biotechnol
. 2:248-254). The effect of redox dyes, with or without electrochemical reduction systems, on metabolite patterns and H
2
production has been examined in several microbial processes, including the glutamate (Hongo, et al., 1979
, Agric. Biol. Chem
. 43:2083-2986), butanol (Girbal, et al., 1995
, Microbiol. Rev
. 16:151-162 and Kim, et al., 1992
, J. Microbiol. Biotechnol
, 2:268-272), and butyrate (Shen, et al., 1996
, Appl. Microbiol, Biotechnol
, 45:355-362) fermentations.
The specific activities of redox enzymes involved in bacterial catabolism, such as hydrogenase or fumarate reductase, can be measured using their in vivo electron carriers (e.g., NAD or menanquinone) or with artificial redox dyes (e.g., benzyl viologen) (Cecchini, et al., 1986
, Proc. Natl. Acad. Sci. USA
83:8898-8902, Dickie, et al., 1979
, Can. J. Biochem
., 57:813-821, Kemner, et al., 1994
, Arch. Microbiol
., 161:47-54, Petrov, et al., 1989
, Arch. Biochem. Bio
-
phys
. 268:306-313, and Wissenbach, et al., 1990
, Arch. Microbiol
. 154:60-66). Bacteria that produce succinic acid as a major catabolic end product (e.g.,
E. coli, Wolinella succinogenes
and other species) have a fumarate reductase (FRD) complex that catalyzes fumarate-dependent oxidation of menaquinone. This reaction is coupled to the generation of a transmembrane proton gradient that is used by the organism to support growth and metabolic function (Kortner, et al., 1992
, Mol. Microbiol
. 4:855-860 and Wissenbach, et al., 1992
, Arch. Microbiol
. 158:68-73). The fumarate reductase of
E. coli
is composed of four nonidentical subunits: FRDA, FRDB, FRDC, and FRDD. The subunits are arranged in two domains: (i) the FRDAB catalytic domain and the FRDCD membrane anchor domain, which is essential for electron transfer and proton translocation reactions involving menaquinone (Cecchini, et al., 1995
, J. Bacteriol
. 177:4587-4592, Dickie, et al., 1979
, Can. J. Biochem
., 57:813-821, and Westenberg, et al., 1990
, J. Biol. Chem
. 265:19560-19567). Subunits FRDA and FRDB retain catalytic activity in solubilized membrane preparations.
Electrochemical techniques employing redox dyes are useful for investigating the oxidation-reduction characteristics of biological systems and provide information about biological energy metabolism (Moreno, et al., 1993
, Eur. J. Biochem
. 212:79-86 and Sucheta, et al., 1993
, Biochemistry
32:5455-5465). Redox dyes that are useful in bioelectrochemical systems must easily react with both the electrode and the biological electron carriers. Many biological electron carriers, such as NAD (Miyawaki, et al., 1992
, Enzyme Microb. Technol
. 14:474-478 and Surya, et al., 1994
, Bioelectrochem. Bioenerg
. 33:71-73), c-type cytochromes (Xie, et al., 1992
, Bioelectrochem. Bioenerg
. 29:71-79), quinones (Sanchez, et al., 1995
, Bioelectrochem. Bioenerg
. 36:67-71), and redox enzymes, such as nitrite reductase (White, et al., 1987
, Bioelectro
-
chem. Bioenerg
. 26:173-179), nitrate reductase (Willner, et al., 1992
, Bioelectrochem. Bioenerg
. 29:29-45), fumarate reductase (Sucheta, et al., 1993
, Biochemistry
. 32:5455-5465), glucose-6-phosphate dehydrogenase (Miyawaki, et al., 1992
, Enzyme Microb. Technol
. 14:474-478), ferredoxin-NADP reductase (Kim, et al., 1992
, J. Microbiol. Biotechnol
. 2:2771-2776) and hydrogenase (Schlereth, et al., 1992
, Bioelectrochem. Bioenerg
. 28:473-482) react electrochemically with the redox dyes.
Certain redox dyes with lower redox potentials than that of NAD, such as methyl viologen (MV) (Kim, et al., 1988
, Biotechnol. Lett
. 10:123-128, Pequin, et al., 1994
, Biotechnol. Lett
. 16:269-274, and White, et al., 1987
, FEMS Microbiol. Lett
. 43:173-176), benzyl viologen (Emde, et al., 1990
, Appl. Environ. Microbiol
. 56:2771-2776), and neutral red (NR) (Girbal, et al., 1995
, FEMS Microbiol. Rev
. 16:151-162 and Kim, et al.,
J. Biotechnol
. 59:213-220) have been correlated with alterations in the rate of biological redox reactions in vivo. Hongo and Iwahara (Hongo, et al., 1979
, Agric. Biol. Chem
. 43A:2075-2081 and Hongo, et al., 1979
, Agric. Biol. Chem
. 43B:2083-2086) discovered that including redox dyes with low &Dgr;E
0
′ values (e.g., MV, benzyl viologen and NR) in bacterial fermentation conducted under cathodic reduction conditions was correlated with an increase in L-glutamate yield (about 6%). In the method of Hongo and Iwahara, a platinum electrode was used to deliver electricity at a level that was sufficiently high to generate hydrogen from water. Therefore, the source of increased reducing power in the method of Hongo and Iwahara is not known, nor was the mechanism by which the tested dyes affect fermentation characterized. Addition of NR to acetone-butanol fermentations is correlated with decreased production of acids and H
2
, and enhanced production of solvent (Girbal, et al., 1995
, FEMS Microbiol. Rev
. 16:151-162 and Kim, et al., 1992
, J. Microbiol. Biotechnol
. 2:2771-2776), an effect that was further enhanced under electroenergized fermentation conditions (Ghosh, et al., 1987
, abstr
. 79
. In Abstracts of Papers
, 194
th ACS National Meeting. American Chemical Society
). Viologen dyes have been used as electron mediators for many electrochemical catalytic systems using oxidoreductases in vitro and in vivo (James, et al., 1988
, Electrochem. Bioenerg
. 20:21-32, Kim, et al., 1988
, Biotechnol. Lett
. 10:123-128, Moreno, et al., 1993
, Eur. J. Biochem
. 212:79-86, Schlereth, et al., 1992
, Bioelectrochem. Bioenerg
. 28:473-482, and White, et al., 1987
, FEMS Microbiol. Lett
. 43:173-
Jain Mahendra K.
Shin Hyoun S.
Zeikus Gregory J.
Michigan State University
Quarles & Brady LLP
Wong Edna
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