DESCRIPTION
MICROORGANISM ABLE TO PRODUCE L-AMINO ACID, AND A METHOD FOR
PRODUCING L-AMINO ACID BY USING THE SAME
Technical Field
The present invention relates to a microorganism able to
produce L-threonine or L-tryptophan and to a method of
producing L-threonine or L-tryptophan using the same.
Background Art
It is known that microorganisms which produce useful
products through fermentation require very large amounts of
energy such as ATP when the biosynthetic pathway is enhanced.
As is known in the art, it is very important that the
intracellular balance between nicotinamide adenine dinucleotide
(NAD(H) ) that is produced by catabolic reactions and
nicotinamide adenine dinucleotide phosphate NADP(H) that is
used in anabolic reactions in microbial metabolic processes.
NAD(H) is an intermediate in the catabolic reactions that
generate ATP through the oxidation of food and functions as an
energy source. And NADP(H) play roles in providing a reducing
power in the in vivo metabolic process, that is providing the
high-energy electrons needed to synthesize molecules by
reacting with enzyme which generally catalyze an anabolic
reactions. The balance therebetween is regulated either by the
phosphorylation of NAD as shown in the following equation 1) or
by the dephosphorylation of NADP as shown in the following
equation 2).
Equation 1)
NAD+ + ATP w NADP+ + ADP
Equation 2)
NADP+ @ NAD+ + phosphate
Thus, in order to effectively produce reducing power such
as NADPH, a phosphate source such as ATP should be increased
together.
ATP (Adenosine-5'-triphosphate) has a high energy
phosphate bond, and generates energy when it is hydrolyzed to
ADP and phosphate . ATP is produced mainly by chemiosmotic
phosphorylation via the electron transport system in
microorganisms or by substrate-level phosphorylation. The
produced ATP is degraded to supply the energy required for
cells and is reused by regenerating via glycolysis pathway or
oxidative phosphorylation.
Based on this fact, studies have been conducted to apply
bacteria's ATP energy regenerating process to the mass
production of useful products in order to facilitate energy
supply (Biosci Biotechnol Biochem., (1997) 61: 840-845) . In
studies on the regeneration of ATP in E. coli, it was found
that the level of ATP in a microorganism is about 150% higher
than that in the parent strain when a few genes, including ysaA
(NCBI Gene ID: 948085), ydaS (NCBI Gene ID: 945923) and ybiX
(NCBI Gene ID: 947502) genes was deficient, respectively, and
this finding was applied to the production of glutathione (FEMS
Microbial Lett., (2009) 297: 217-224) . However, there was no
direct report directly explains the increase in production of
amino acids caused by attenuation in the activities of proteins
that are encoded by the genes.
Disclosure
Technical Problem
The present inventors have found that increasing the
intracellular level of ATP, which is used as the most
plentiful energy source in cells producing L-amino acid, is
effective to increase the production of L-threonine or Ltryptophan,
thereby completing the present invention.
An object of the present invention is to provide a
recombinant E. coli strain which has an increased L-threonine
or L-tryptophan productivity by increasing the productivity of
ATP .
Another object of the present invention is to provide a
method of producing L-threonine or L-tryptophan using the
recombinant E. coli strain.
Technical Solution
In order to accomplish the above objects, an embodiment
of the present invention provides an L-threonine or Ltryptophan
producing recombinant E. coli strain, wherein the
strain is modified to attenuate (weaken) activity of at least
one protein selected from the group consisting of a protein
YsaA having an amino acid sequence represented by SEQ ID NO: 2,
a protein YdaS having an amino acid sequence represented by SEQ
ID NO: 4, and a protein YbiX having an amino acid sequence
represented by SEQ ID NO: 6.
An embodiment of The present invention also provides a
method for producing L-threonine or L-tryptophan, which
comprises culturing the recombinant E. coli strain.
Advantageous Effects
The present invention provides a recombinant
microorganism whose L-threonine or L-tryptophan productivity
is improved by increasing the intracellular ATP level in a
microorganism having L-threonine or L-tryptophan productivity.
According to the present invention, it provides a method to
enhance production of L-threonine or L-tryptophan by
recovering the balance of energy metabolism to increase the
cellular activity and reduce the culture time.
Description of Drawings
FIG. 1 shows the relative ATP level (%) of an Lthreonine-
producing strain relative to that of its parent
strain.
FIG. 2 shows the relative ATP level (%) of a Ltryptophan-
producing strain relative to that of its parent
strain.
Best Mode
Hereinafter, the present invention will be described in
detail.
An embodiment of the present invention provides an Lthreonine
or L-tryptophan producing recombinant E. coli
strain, wherein the strain is modified to attenuate activity
of at least one selected from the group consisting of a
protein YsaA having an amino acid sequence represented by SEQ
ID NO: 2, a protein YdaS having an amino acid sequence
represented by SEQ ID NO: 4, and a protein YbiX having an
amino acid sequence represented by SEQ ID NO: 6.
An L-threonine or L-tryptophan producing microorganism
that may be used in the present invention may be any
microorganism capable of producing L-threonine or Ltryptophan,
such as Escherichia sp. Bacterium, E. coli,
Coryneform bacterium, Serratia sp. bacterium, Providencia sp.
bacterium, or the like. Specifically, a microorganism
belonging to the genus Escherichia may be used.
In a specific embodiment of the present invention,
recombinant E. coli strain CJ600 (KCCM 10812P) (Korean Patent
Registration No. 10-0792095) having L-tryptophan productivity
is used, which is obtained by genetically engineering an
recombinant E. coli strain (KFCC 10066) having L-phenylalanine
productivity so as to desensitize the tryptophan auxotrophy,
block L-phenylalanine biosynthesis and enhance tryptophan
biosynthesis-related genes.
In another specific embodiment of the present invention,
recombinant E. coli strain FTR2533 (KCCM-10541) (Korean Patent
Registration No. 10-0576342) having L-threonine productivity is
used, which is obtained by genetically engineering an E. coli
mutant strain (KFCC 10718) having L-threonine productivity so
as to inactivate the wild-type galR gene.
YsaA, a protein having an amino acid sequence represented
by SEQ ID NO: 2, is predicted a hydrogenase of 4Fe-4s
ferredoxin-type component, but its exact function has not yet
been found.
YdaS, a protein having an amino acid sequence represented
by SEQ ID NO: 4, is predicted a DNA binding transcription
regulator, but its exact function has not yet been found.
YbiX, a protein having an amino acid sequence represented
by SEQ ID NO: 6, is one of the Fe(I1)-dependent oxygenase
superfamily, which functions as an oxidoreductase that oxidizes
its substrate using oxygen.
The polypeptides YsaA, YdaS and YbiX of the present
invention have the amino acid sequences represented by SEQ ID
NOS: 2, 4 and 6, respectively, but are not limited thereto,
because the amino acid sequences of the proteins may depending
on the species or strains of microorganisms.
In other words, the proteins of the present invention may
be mutants or artificial variants encoding a protein that has
an amino acid sequence including a substitution, deletion,
insertion, addition or inversion of one or several amino acids
in one or more positions of the amino acid sequence represented
by SEQ ID NO: 2, 4 or 6, as long as the mutants or artificial
variants can be helpful in increasing the production of amino
acid by attenuating the activities described in the present
invention. Herein, the number of "several" amino acids differs
depending on the position or type of amino acid residues in the
three-dimensional structure of the protein, but is particularly
2-20, specifically 2-10, and more specifically 2-5. In
addition, this substitution, deletion, insertion, addition or
inversion of amino acids also include those alterations caused
by a naturally occurring mutation or artificial variation based
on the difference in individuals or species of microorganisms
having the activity of the polypeptides.
As used herein, the term "attenuation" means that the
activity of a protein is weakened either by deleting part or
all of the gene encoding the protein, or by modifying an
expression regulatory sequence to reduce the expression of the
gene, or by modifying the chromosomal gene sequence to weaken
the activity of the protein, or by combinations thereof.
In the present invention, attenuation of the activity may
be achieved by a method selected from the group consisting of:
1) deleting part or all of a polynucleotide encoding the
protein; 2) modifying an expression regulatory sequence to
reduce the expression of the polynucleotide; 3) modifying the
chromosomal polynucleotide sequence to weaken the activity of
the protein; and 4) combinations thereof.
The method for deletion of part or all of the
polynucleotide encoding the protein may be performed by
replacing a polynucleotide which encodes an endogenous target
protein in the chromosome, with either a polynucleotide that a
part of nucleic acid sequence is deleted or a marker gene
through chromosome insertion vector.
Herein, the term "a part of" nucleic acid sequence differ
depending on the kind of gene, but is regardless of the
position thereof, and it is specifically 1-200, mor
specifically 1-100, and even more specifically 1-50.
Also, the method of modifying the expression regulatory
sequence to reduce the expression of the polynucleotide may be
performed either by inducing a mutation in the expression
regulatory sequence by the deletion, insertion, nonconservative
or conservative substitution, or combinations
thereof, of one or more nucleotides to attenuate the activity
of the expression regulatory sequence, or by replacing the
expression regulatory sequence with weaker activity. The
expression regulatory sequence includes a promoter, an operator
sequence, a sequence encoding a ribosome-binding site, a
sequence regulating the termination of transcription and
translation.
In addition, the method of modifying the chromosomal
polynucleotide sequence encoding the protein of the present
invention may be performed either by inducing a mutation in the
sequence by the deletion, insertion, non-conservative or
conservative substitution, or combinations thereof, of one or
more nucleotides to attenuate the activity of the sequence, or
by replacing the sequence with an modified nucleotide sequence
having weaker activity.
The polynucleotide encoding the protein of the present
invention can be introduced into a host cell and may be
substituted with a codon difficult to express in the host. In
addition, the N-terminus or C-terminus thereof may be extended
or deleted, and the start codon may be modified to regulate the
expression level.
Each of the polynucleotides of the present invention may
have a polynucleotide sequence encoding a protein having a
homology of at least 80%, specifically at least 90%, more
specifically at least 95%, and even more specifically at least
97% to the amino acid sequence of each represented by SEQ ID
NOS: 2, 4 and 6, as long as the polynucleotide can attenuate
the protein activity of the variant. More specifically, the
polynucleotides have a polynucleotide sequence represented by
SEQ ID NOS: 1, 3 and 5, respectively.
As used herein, the term "homology" refers to the identity
between two amino acid sequences. The homology can be
determined using well-known methods, for example, the computer
program BLAST 2.0 which calculates parameters like as score,
identity, and similarity.
Also, the pol ynucleotide sequences of the present
invention may be hybridized with the polynucleotide sequences
represented by SEQ ID NOS: 1, 3 and 5 and probes produced from
the above-described nucleotide sequences under stringent
conditions, and may be modified sequences encoding normally
functioning proteins.
As used herein, the term "stringent conditions" refers to
conditions that allow specific hybridization between
polynucleotides. Alternatively, the term is related to
polypeptides or proteins, including derivatives thereof
(Molecular Cloning, A Laboratory Manual, J. Sarnbrook et al.,
Editors, 2nd Edition, Cold Spring Harbor Laboratory press, Cold
Spring Harbor, New York, 1989; or Current Protocols in
Molecular Biology, F.M. Ausubel et al., Editors, John Wiley &
Sons, Inc., New York) .
Specifically, the "stringent conditions" refer to
hybridization at 65 O C in hybridization buffer (3.5xSSC, 0.02%
Ficoll, 0.02% polyvinylpyrrolidone, 0.02% bovine serum albumin,
2.5 mM NaH2P04 (pH 7) , 0.5% SDS, 2 mM EDTA) . SSC is 0.15 M
sodium chloride/0.15 M sodium citrate at pH 7. A£ ter
hybridization, the membrane to which the DNA has been
transferred is washed in 2xSSC at room temperature and then in
0.1-0.5xSSC/O. lxSDS at 68 c.
As used herein, the term "vector" refers to a DNA
construct containing the nucleotide sequence of a target
protein-encoding gene operably linked to a suitable regulatory
sequence so as to be able to express the target gene in a
suitable host cell. The regulatory sequence includes a
promoter capable of initiating transcription, any operator for
regulating this transcription, a sequence encoding a suitable
rnRNA ribosome binding site, and a sequence for regulating the
termination of transcription and translation. Once transformed
into a suitable host, the vector may replicate or function
independently of the host genome, or may, in some cases,
integrate into the genome itself.
The vector that is used in the present invention is not
specifically limited and may be any vector known in the art, as
long as it can replicate in a host. Examples of the commonly
used vectors may include natural or recombinant plasmids,
cosmids, viruses, and bacteriophages. For example, the phage
vector or cosmid vectors include pWE15, M13, ABL3, ABL4, UII,
ASHII, APII, A10, All, Charon4A, and Charon21A, and the plasmid
vectors include pBR, pUC, pBluescriptI1 pGEM, PTZI pCL1920 and
PET-type plasmids. Vectors that may be used are not
particularly limited, and any known expression vectors may be
used. Specifically, pACYC177, pACYC184, pC~1920, P E C C G ~ ~ ~ ,
pUC19, pBR322, pMW118 or pCClBAC vectors may be used. Most
specifically, pACYC177, pCL1920 and pCClBAC vectors may be
used.
Further, the vector that is used in the present invention
is a vector capable of transforming host cells, to insert the
polynucleotide encoding the target protein into the chromosome
of the host cell. Specific examples of the vector include, but
are not limited to, the shuttle vector pECCG112 that can selfreplicate
in both directions in E. coli and Coryne-type
bacteria (Kap-Soo, Noh, Kor. Jour. Microbial. July 1991, p149-
154) .
Also, the polynucleotide encoding the endogenous target
protein in the chromosome can be replaced with a new
polynucleotide by a vector for insertion into the bacterial
chromosome. Insertion of the polynucleotide into the
chromosome can be performed by any method known in the art, for
example, homologous recombination. Because the vector of the
present invention can be inserted into the chromosome by
homologous recombination, it may further comprise a selection
marker for confirming its insertion into the chromosome. The
selection marker is used to select a cell transformed with the
vector, that is, confirm the insertion of the target
polynucleotide. The selection marker that is used in the
present invention may be selected from markers that provide
selectable phenotypes, such as drug resistance, auxotrophy,
resistance to cytotoxic agents, or surface protein expression.
Only cells expressing the selection marker are able to survive
or to show different phenotypes under the environment treated
with the selective agent, and thus the transformed cells can be
selected.
As used herein, the term 'transformation" means
introducing a vector comprising the polynucleotide encoding the
target protein into a host cell so as to be able to express the
protein encoded by the polynucleotide in the host cell. The
transformed polynucleotides include all the genes inserted in
the chromosome of the host cell or located outside the
chromosome, as long as they can be expressed in the host cell.
In addition, the polynucleotides include DNA and RNA, which
encode the target protein. As long as the polynucleotide can
be introduced in the host cell and expressed therein, the gene
may be introduced in any form.
For example, the polynucleotide can be introduced into the
host cell in the form of an expression cassette which is a
polynucleotide construct including all elements for expressing
the gene. The expression cassette includes a promoter which is
operably linked to the gene, a transcription termination
signal, a ribosome binding site, and a translation termination
signal. The expression cassette may be in the form of an
expression vector capable of self-replicating. The
polynucleotide may also be introduced into the host cell by
itself, and be operably linked to the sequence necessary for
expression in the host cell.
Specifically, attenuation of the activity of the protein
that is encoded by the ysaA, ydaS or ybiX gene may be achieved
by deletion of the gene. Specifically, a mutation in the gene
can be induced using chemicals or light such as UV light,
thereby obtaining a variant having the deleted gene.
Alternatively, a variant lacking the activity of the protein
can be obtained by substituting the chromosomal gene to the
nucleotide lacking the activity by a gene recombination
technique, by a method of gene replacementthruough homologous
recombination.
Also, an embodiment of the present invention also provides
a method for producing L-threonine or L-tryptophan, the method
comprising culturing an L-threonine or L-tryptophan producing
recombinant E. coli strain, wherein the strain is modified to
attenuate activity of at least one selected from the group
consisting of a protein YsaA having an amino acid sequence
represented by SEQ ID NO: 2, a protein YdaS having an amino
acid sequence represented by SEQ ID NO: 4, and a protein YbiX
having an amino acid sequence represented by SEQ ID NO: 6.
The culture process of the present invention can be
performed in suitable media and culture conditions known in the
art. This culture process can be easily modified by any person
skilled in the art depending on the type of strain selected.
Examples of the culture process include, but are not limited to,
batch culture, continuous culture, and fed-batch culture.
The media and culture conditions that are used in culture
of the microorganism of the present invention may be those as
long as that are used in culture of microorganisms belonging to
the genus Escherichia, but these should properly satisfy the
requirements of the microorganism of the present invention.
In a specific embodiment of the present invention, the
microorganism may be cultured in a conventional medium
containing suitable carbon sources, nitrogen sources, amino
acids, vitamins and the like under aerobic conditions while
adjusting temperature, pH and the like.
Carbon sources that may be used in the present invention
include carbohydrates such as glucose, fructose, sucrose,
maltose, mannitol, sorbitol; alcohols such as sugar alcohol,
glycerol, pyruvic acid, lactic acid and citric acid; and amino
acids such as organic acid, glutamic acid, methionine and
lysine. In addition, natural organic nutrient sources such as
starch hydrolysates, molasses, blackstrap molasses, rice bran,
cassava, bagasse and corn steep liquor may be used.
Specifically, the organic nutrient sources include glucose and
sterile pretreated molasses ( e l molasses converted to
reduced sugars), and suitable amounts of carbon sources may be
used without limitation.
Nitrogen sources that may be used in the present invention
include inorganic nitrogen sources such as ammonia, ammonium
sulfate, ammonium chloride, ammonium acetate, ammonium
phosphate, ammonium carbonate, and ammonium nitrate; amino
acids such as glutamic acid, methionine and glutamine; and
organic nitrogen sources such as peptone, NZ-amine, meat
extract, yeast extract, malt extract, corn steep liquor, casein
hydrolysate, fish meal or its digested product, defatted
soybean cake or its digested product, etc. These nitrogen
sources may be used alone or in combination. The medium may
contain potassium phosphate monobasic, potassium phosphate
dibasic and corresponding sodium-containing salts, as
phosphorus sources.
Inorganic compounds that may be used in the present
invention include sodium chloride, calcium chloride, iron
chloride, magnesium sulfate, iron sulfate, manganese sulfate
and calcium carbonate. In addition, the medium may contain
amino acids, vitamins and suitable precursors. These media or
precursors may be added to the medium in a batch or continuous
manner.
Compounds such as ammonium hydroxide, potassium hydroxide,
ammonia, phosphoric acid and sulfuric acid may be added to the
medium in a suitable manner during culture to adjust the pH of
the culture medium.
In addition, during culture, a defoaming agent such as
fatty acid polyglycol ester may be used to suppress the
formation of bubbles. Further, in order to maintain the
culture medium in an aerobic state, oxygen or oxygen-containing
gas may be injected into the culture medium. In addition, in
order to maintain the culture medium in an anaerobic or nonaerobic
state, no gas is injected, or nitrogen, hydrogen or
carbon dioxide gas may be injected into the culture medium.
The culture medium is typically maintained at a temperature
ranging from 27 °C to 37 O C , and specifically from 30 'C to
35 'C. Culture of the microorganism can be continued until the
desired level of the useful substance will be obtained.
Specifically, the culture period is from 10 to 100 hours.
The method of the present invention may further comprise
purifying or recovering the L-amino acid produced in the
culture step. The purification or recovery process can be
performed by purifying or recovering the desired L-amino acid
from the culture medium using a suitable method selected
depending on the method used for culture of the microorganism,
for example, a batch, continuous or fed-batch culture method.
Hereinafter, the present invention will be described in
further detail with reference to examples. It is to be
understood, however, that these examples are for illustrative
purposes and are not intended to limit the scope of the present
invention.
Examples
Example 1: Construction of L-threonine and L-tryptophan
producing strains having attenuated activity of protein that is
encoded by ysa., ydaS or y b i X qene
In this Example, each of the ysaA, ydaS and ybiX gene in
the L-tryptophan producing strain KCCM10812P (Korean Patent
Registration No. 10-0792095) and the L-threonine producing
strain KCCM10541 (Korean Patent Registration No. 10-0576342)
was deleted by homologous recombination.
The L-tryptophan producing parent strain KCCM10812P is a
strain derived from an E. coli variant KFCC 10066 having Lphenylalanine
productivity. It is a recombinant E. coli strain
having L-tryptophan productivity, characterized in that
chromosomal tryptophan auxotrophy was desensitized, the pheA,
trpR, mtr and tnaAB genes were attenuated and the aroG and t r p E
genes were modified.
Also, the L-threonine producing parent strain KCCM10541 is
a strain derived from E. coli KFCC10718 (Korean Patent Laid-
Open Publication No. 1992-0008365). It has resistance to Lmethionine
analogue, a methionine auotroph phenotype,
resistance to L-threonine analogue, a leaky isoleucine
auxotroph phenotype, resistance to L-lysine analogue, and
resistance to a-aminobutyric acid, and is capable of producing
L-threonine.
The ysaA, ydaS and ybiX genes to be deleted have the
polynucleotide sequences represented by SEQ ID NOS: 1, 2 and 3,
respectively.
For this purpose, the one-step inactivation method
(developed by Datsenko KA et al.) that is a mutagenesis
technique using lambda red recombinase was used (Proc Natl Acad
Sci USA., (2000) 97: 6640-6645). As a marker for confirming
insertion into the genes, the chlorarnphenicol-resistant gene of
pUCprmfmloxC was used (Korean Patent Laid-Open Publication No.
2009-0075549) .
About 1200-bp gene fragments were amplified by polymerase
chain reaction (hereinafter referred to as PCR) using
pUCprmfmloxC as a template and a pair of primers 1 and 2, a
pair of primers 7 and 8 and a pair of primers 13 and 14, which
have a portion of each of the three genes and a portion of the
chloramphenicol-resistant gene of pUCprmfmloxC. The PCR was
performed for 30 cycles, each consisting of denaturation at
94 for 30 sec, annealing at 55 "C for 30 sec and extension at
72 % for 1 min.
Table 1
Primer
No.
Sequax;e SEQ
ID
NO
Also, the DNA fragments obtained by the PCR amplification
were electrophoresed on 0.8% agarose gel, and then eluted and
used as templates in secondary PCR. Secondary PCR was
performed so that the 5' and 3' terminal regions of the primary
DNA fragments had 20 pairs of complementary nucleotide bases.
About 1300-bp gene fragments were amplified by PCR using the
eluted primary PCR products as templates and a pair of primers
3 and 4, a pair of primers 9 and 10 and a pair of primers 15
and 16, which have include the 5' and 3' regions of the genes.
The PCR was performed for 30 cycles, each consisting of
denaturation at 94 O C for 30 sec, annealing at 55 for 30 sec
and extension at 72 'C for 1 min. The DNA fragments obtained by
the PCR amplification were electrophoresed on 0.8% agarose gel,
and then eluted and used in recombination.
According to the method developed by Datsenko KA et al.
(Proc Natl Acad Sci USA., (2000) 97:6640 6645), an E. coli
strain transformed with a pKD46 were made competent, and then
transformed with the 1300-bp gene fragments obtained by PCR.
The resulting strains were selected on LB medium having
resistance to chloramphenicol. PCR was performed using a pair
of primers 5 and 6, a pair of primers 11 and 12 and a pair of
primers 17 and 18, and the amplification products had sizes of
1450, 1530 and 1640 bp, respectively, and were confirmed that
the genes were deleted.
pKD46 was removed from the primary recombinant strains
having chlorarnphenicol resistance, and then a pJW168 vector was
introduced into the strains, and the chloramphenicol marker
gene was removed from the bacterial cells (Gene, (2000)
247,255-264). The resulting bacterial cells were about 400-bp,
500-bp and 600-bp amplification products obtained by a pair of
primers 5 and 6, a pair of primers 11 and 12 and a pair of
primers 17 and 18, and were confirmed that the desired gene
deletion was achieved.
According to the above-described method, the L-threonine
producing strains KCCM10541 AysaA, KCCM10541 AydaS and
KCCM10541 AybiX were constructed. Also, the L-tryptophan
producing strains KCCM10812P AysaA, KCCM10812P AydaS and
KCCM10812P AybiX were constructed.
Example 2: Construction of recombinant L-threonine and Ltryptophan
producing strains having deletion of two or more of
ysaA , ydaS and @iX genes
According to the method described in Example, recombinant
strains having a deletion of two or more of the genes were
constructed.
A pKD46 vector for using lambda red recombinase was
introduced into the strains having a deletion of any one of the
genes, and then the strains were made competent. Also, gene
fragments amplified by PCR to include a portion of the three
genes and the chloramphenicol-resistant gene of pUCprmfmloxC
were transformed into different strains having a deletion of
one of the genes. The resulting strains were screened on LB
medium having chloramphenicol resistance, and deletion of a
combination of the genes was confirmed by the use of the primer
pairs described in Example 1.
According to the above-described method, the L-threonine
producing strains KCCM10541 AysaA AydaS, KCCM10541 AydaS AybiX,
KCCM10541 AybiX DysaA and KCCM10541 AysaA AydaS AybiX were
constructed. Also, the L-tryptophan producing strains
KCCM10 8 12 P DysaA Ayda S, KCCM10 8 12 P AydaS AybiX, KCCMl0 8 12 P
DybiX AysaA and KCCM10812P AysaA AydaS AybiX were constructed.
Among the recombinant strains obtained as described above,
KCCM10541 AysaA AydaS AybiX and KCCM10812P AysaA AydaS
AybiX were named "E. coli CA03-4257P" and ' E . coli CA04-
2002", respectively, and deposited at the Korean Culture
Center of Microorganisms (361-221, Hongje 1-dong,
Seodaemun-gu, Seoul, Korea), an international depository
authority, on December 29, 2011 under the accession
numbers KCCM11243P and KCCM11245PI respectively.
Example 3: Measurement of levels of ATP in constructed Lthreonine
producing strains and L-tryptophan producing strains
In this Example, the levels of ATP in the strains
constructed in Examples 1 and 2 were quantitatively measured.
For this purpose, the method developed by Kiyotaka Y. Hara
et al., which uses luciferase, was used ("An Efficient Method
for Quantitative determination of Cellular ATP Synthetic
Activity", J Biom Scre, (2006) Vll:No.3:PP310-17).
Specifically, the strains having different genetic
characters were cultured overnight in LB liquid medium
containing glucose. The supernatant was removed by
centrifugation, the bacterial cells were washed with 100 mM
Tris-C1 (pH 7 . 5 ) , and then treated with PB buffer (permeable
buffer: 40% [v/v] glucose, 0.8% [v/v] Triton X-100) for 30
minutes to release intracellular ATP. Next, the supernatant
was removed by centrifugation, and luciferin as a substrate for
luciferase was added to the cells. The cells were allowed to
stand for 10 minutes, and then luciferase activity in the cells
was measured with a lurninometer to quantitatively determine the
ATP level. The results of the measurement are shown in FIGS. 1
and 2. All the results were recorded as the average of three
repeated experiments.
As can be seen in FIGS. 1 and 2, the levels of ATP in the
strains constructed from the L-threonine producing strain and
the L-tryptophan producing strain in Examples 1 and 2 all
increased. In addition, the ATP level was higher in the
strains having a deletion of a combination of the genes than in
the strains having a deletion of one of the gene.
Example 4: Examination of titer of L-threonine producing
strain, which has attenuated activity of alone or a combination
of enzymes that are encoded by ysaA, ydaS and ybiX qene, in
glucose-containinq medium
According to the methods described in Examples 1 and 2,
alone or a combination of the ysaA, ydaS and ybiX genes was
deleted from the L-threonine producing strain KCCM10541 (Korean
Patent Registration No. 10-0576342) to increase the
intracellular ATP level. The titers of the resulting strains
were evaluated using glucose as a carbon source.
Specifically, the strains having different genetic
characters were cultured overnight on LB solid medium in an
incubator at 33 "C and inoculated by a platinum loop into 25 mL
of glucose-containing medium having the composition shown in
Table 2 below. Then, the strains were incubated in an
incubator at 33 'C and at 200 rpm for 50 hours. The results are
shown in Table 3 below. All the results were recorded as the
average of three flask results.
Table 2
Table 3
Composition
Glucose
KH2po4
(NH4 ) 2S04
MgS04 .H20
FeS04 .H20
MnS04 .H20
Yeast extract
Calcium carbonate
PH
Concentration (per liter)
70 g
2
25 g
1 g
5 mg
5 mg
2 g
30 g
6.8
consumption
I ~ -
KCCM10541 AysaA
-
K- .C- C --M -1 - 0- 5- 4- 1- DvdaS -L
KCCM10541 DybiX
KCCM10541 AysaA DydaS
KCCM10541 A ydsS DybiX
* measured at 30 hours
24.6
23.5
KCCM10541 DybiX DysaA
r,mmfil nc A ? n . . - - n A . . A , C A
** measured at 50 hours
22.7
24.9
24.5
As can be seen in Table 3 above, we have demonstrated that
33.4
34.7
25.0
the glucose utilization of the recombinant L-threonine
32.2
33.0
33.9
35.1
3 6
producing E.coli strains constructed according to the present
32.7
32.9
33.1
I
invention increased by up to about 22% compared to that of the
parent strain, and the production of threonine of the
32.1
recombinant strains increased by up to about 7% compared to
33.0
that in the parent strain. In view of the ATP level shown in
1
FIG. 1, these results indicate that the glucose consumption
rate or amino acid productivity of the recombinant strains was
increased by the increased ATP level.
Example 5: Examination of titer of L-threonine producinq
strain, which has attenuated activity of alolne or a
combination of enzymes that are encoded by ysaA, ydaS and ybiX
qene, in sucrose-containinq medium
According to the methods described in Examples 1 and 2,
alone or a combination of the ysad, ydaS and ybiX genes was
deleted from the L-threonine producing strain KCCM10541 (Korean
Patent Registration No. 10-0576342) to increase the
intracellular ATP level. The titers of the resulting strains
were evaluated using sucrose as a carbon source.
Specifically, the strains having different genetic
characters were cultured overnight on LB solid medium in an
incubator at 33 O C and inoculated by a platinum loop into 25 mL
of sucrose-containing medium having the composition shown in
Table 4 below. Then, the strains were incubated in an
incubator at 33 % and at 200 rpm for 48 hours. The results are
shown in Table 5 below. All the results were recorded as the
average of three flask results.
Table 4
Composition
Sucrose
KH2P04
(NH4 I 2S04
MgS04 .H20
FeS04 .H20
MnS04 .H20
Yeast extract
Calcium carbonate
PH
Concentration (per liter)
70 g
2 g
25 g
1 g
5 mg
5 mg
2 g
30 g
6.8
Table 5
* measured at 24 hours
KCCM10541 A y s a A A y d a S
KCCM10541 A d s S A y b i X
KCCM10541 A y b i X A y s a A
KCCM10541 A y s a A A y d a S A y b i X
** measured at 48 hours
L-threonine
(g/L) **
As can be seen in Table 5 above, we have demonstrated that
sucrose
consumption
(ff/L) *
Strain
27.5
27.2
28.3
27.9
the sucrose utilization of the recombinant L-threonine
OD
producing E-coli strains constructed according to the present
42.1
43.0
42.8
43.9
invention increased by up to about 10% compared to that of the
38.0
38.1
38.7
38.9
parent strain, and the production of threonine of the
recombinant strains increased by up to about 5% compared to
that in the parent strain. In view of the ATP level shown in
FIG. 1, these results indicate that the activity and sucrose
consumption rate or amino acid productivity of the recombinant
strains were increased by the increased ATP level.
Example 6: Examination of titer of L-tryptophan producing
strain, which has attenuated activity of alone or a combination
28
of enzymes that are encoded by ysa., ydaS and y b i X gene, in
glucose-containing medium
According to the methods described in Examples 1 and 2,
alone or a combination of the ysaA, ydaS and ybiX genes was
deleted from the L-tryptophan producing strain KCCM10812P
(Korean Patent Registration No. 10-0792095) to increase the
intracellular ATP level. The titers of the resulting strains
were evaluated using glucose as a carbon source.
In order to examine the titer, the strains were inoculated
by a platinum loop on LB solid medium and then cultured
overnight in an incubator. And, it was inoculated by a
platinum loop into 25 mL of flask titer medium having the
composition shown in Table 6 below. Then, the strains were
incubated in an incubator at 37 "C and at 200 rpm for 48 hours.
The results are shown in Table 7 below. All the results were
recorded as the average of three flask results.
Table 6
Composition
Glucose
K2HP04
(NH4 ) 2S04
NaCl
MgS04 .H20
Sodium citrate
Yeast extract
Calcium carbonate
Sodium citrate
Concentration (per liter)
60 g
1 (2
10 (3
1 g
1 g
5 g
2 g
40 g
5 g
Table 7
Phenylalanine
Tyrosine
PH
0.15 g
0.1 g
6.8
* measured at 33 hours
** measured at 48 hours
As can be seen in Table 7 above, we have demonstrated that
the glucose consumption of the recombinant L-threonine
producing E. coli strains constructed according to the present
invention increased by up to about 10% compared to that of the
parent strain, and the production of tryptophan of the
recombinant strains increased by up to about 38% compared to
that in the parent strain. In view of the ATP level shown in
FIG. 2, these results indicate that the activity and glucose
consumption rate or amino acid productivity of the recombinant
strains were increased by the increased ATP level.
L-tryptophan
(g/L) **
5.7
6.9
6.6
6.0
7.5
7.6
7.3
7.9
Glucose
consumption
(g/L) *
47.2
48.3
49.1
5 0
48.4
49.3
4 9
51.9
Strain
KCCM10812P
KCCM10812P AysaA
KCCM10812P AydaS
KCCM10812P AybiX
KCCM10812P AysaAnydaS
KCCM10812P AydaSAybiX
KCCM108 12P AybiXAysaA
KCCM10812P AysaAnydaSAybiX
OD
18.2
18.3
18
17.7
17.9
18.7
19.9
18.9
While the present invention has been described with
reference to the particular illustrative embodiments, those
skilled in the art to which the present invention pertains can
understand that the present invention may be embodied in other
specific forms without departing from the technical spirit or
essential characteristics of the present invention. Therefore,
the embodiments described above are considered to be
illustrative in all respects and not restrictive. Furthennore,
the scope of the present invention is defined by the appended
claims rather than the detailed description, and it should be
understood that all modifications or variations derived from
the meanings and scope of the present invention and equivalents
thereof are included in the scope of the appended claims.
Accession Number
Depository authority: Korean Culture Center of
Microorganisms (International)
Accession Number: KCCM11243P
Deposition date: December 29, 2011
Depository authority: Korean Culture Center of
Microorganisms (International)
Accession Number: KCCM11245P
Deposition date: December 29, 2011

CLAIMS
1. An L-threonine or L-tryptophan producing recombinant
E. coli strain, wherein the strain is modified to attenuate
activity of at least one selected from the group consisting of
a protein YsaA having an amino acid sequence represented by SEQ
ID NO: 2, a protein YdaS having an amino acid sequence
represented by SEQ ID NO: 4, and a protein YbiX having an
amino acid sequence represented by SEQ SD NO: 6.
2. The L-threonine or L-tryptophan producing
recombinant E. coli strain according to claim 1, wherein the
protein YsaA is encoded by a polynucleotide sequence
represented by SEQ ID NO: 1, the protein YdaS is encoded by a
polynucleotide sequence represented by SEQ ID NO: 3, and the
protein YbiX is encoded by a polynucleotide sequence
represented by SEQ ID NO: 5.
3. The L-threonine or L-tryptophan producing
recombinant E. coli strain according to claim 1, wherein the
recombinant E. coli strain is L-threonine producing
Escherichia coli CA03-4257P (KCCM11243P) .
4. The L-threonine or L-tryptophan producing
recombinant E. coli strain according to claim 1, wherein the
recombinant E. coli strain is L-tryptophan producing
Escherichia coli CA04-2002 (KCCM11245P) .
5. A method for producing L-threonine or L-tryptophan,
the method comprising culturing an L-threonine or L-tryptophan
producing recombinant E. coli strain, wherein the strain is
modified to attenuate activity of at least one selected from
the group consisting of a protein (YsaA) having an amino acid
sequence represented by SEQ ID NO: 2, a protein (YdaS) having
an amino acid sequence represented by SEQ ID NO: 4, and a
protein (YbiX) having an amino acid sequence represented by in
SEQ ID NO: 6.
6. The method according to claim 5, wherein the
recombinant E. coli strain is L-threonine producing
Escherichia coli CA03-4257P (KCCM11243P).
7. The method according to claim 5, wherein the
recombinant E. coli strain is L-tryptophan producing
Escherichia coli CA04-2002 (KCCM11245P) .