optimization of medium composition for the production
TRANSCRIPT
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BIOTECHNOLOGICAL PRODUCTS AND PROCESS ENGINEERING
Optimization of medium composition for the production
of alkaline -mannanase by alkaliphilic Bacillus sp. N16-5
using response surface methodology
Shan-shan Lin &Wen-fang Dou &Hong-yu Xu &
Hua-zhong Li &Zheng-Hong Xu &Yan-he Ma
Received: 12 November 2006 /Revised: 22 February 2007 /Accepted: 24 February 2007 / Published online: 15 March 2007# Springer-Verlag 2007
Abstract In this work, a 22 factorial design was employed
combining with response surface methodology (RSM) tooptimize the medium compositions for the production of
alkaline -mannanase by alkaliphilic Bacillus sp. N16-5
isolated previously from sediment of Wudunur Soda Lake
in Inner Mongolia, China. The central composite design
(CCD) used for the analysis of treatment combinations
showed that a second-order polynomial regression model
was in good agreement with experimental results, with R2=
0.9829 (P
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Xanthomonas campestris, Aeromonas hydrophila, Tricho-
derma sp. made known to the public consecutively (Ma et
al.1991). In 1987, an alkaline -mannanase was found for
the first time by Akino from alkaliphilic Bacillus sp.
AM001 and the possibility of the application was proposed
(Akino et al.1987,1989). In our previous work, an alkaline
-mannanase produceralkaliphilic Bacillus sp.N16-5
has been isolated from the sediment of Wudunur Soda Lakein Inner Mongolia, China (Ma et al. 1991). This enzyme
was demonstrated to be a novel alkaline -mannanase
(optimum pH 9.5) and has a fine prospect of application
in the enzymatic production of mannooligosaccharide,
which is one of the growth factors of Bifidobacteriumsp.
(Ma et al. 2004). Recently, Hatada et al. cloned and
characterized a high-alkaline -mannanase (up to pH 10)
from an alkaliphilic Bacillus sp. strain JAMB-750 (Hatada
et al.2005).
It has become a bottleneck problem for industrial
application of extremozymes that the extremophiles directly
isolated from nature have some shortcoming for extrem-ozyme production, such as longer generation time, lower
biomass yield leading to the lower productivity of the
extremozymes, and higher production costs (Adams et al.
1995; Schiradi and De Rose 2002). To overcome these
problems, some approaches were proposed as follows: (1)
optimization of fermentation bioprocesses and media
design; (2) implementation of innovative bioreactors; and
(3) overproduction in mesophilic hosts. Some attempts
were made to increase the production from the wild/mutant
strains by optimization of the culture conditions; however,
up to now, the research in this field has not been so mature
(Heck et al. 2005a). As mentioned above, some genes of
alkaline -mannanase from alkaliphiles have been cloned,
sequenced, and expressed in the mesophiles host Escher-
ichia coli and B. substilis (Akino et al. 1989; Hatada et al.
2005). For their low expression level, they were hardly to
be successfully applied in the industries. In our previous
work, we have cloned the alkaline -mannanase gene of
strain N16-5 (Ma et al.2004), and tried to overexpress it in
Pichia pastoris and B. subtilis, but the expression levels
were also comparatively low (data not shown). Interesting-
ly, the wild alkaliphilic Bacillus sp.N16-5 showed high
ability to produce extracellular alkaline -mannanase (Ma
et al. 1991). Therefore, improvement of the fermentation
process and media design of this wild producer to enhance
the capacity of alkaline -mannanase production could be
another possible option.
Response surface methodology (RSM), which has been
extensively applied in optimization of medium composi-
tion, conditions of enzymatic hydrolysis, fermentation, and
food manufacturing processes (Cui et al. 2006), is the
collection of statistical techniques for experiment design,
model development, evaluation factors, and optimum
conditions search. To improve the alkaline -mannanase
production by alkaliphilic Bacillus sp.N16-5, Pluckett
Burman (PB) design, Central composite design (CCD),
and experimental factorial design can be employed to
optimize the medium compositions for enzyme production,
and perform a minimum number of experiments.
In this paper, the objective was to optimize the medium
compositions for the cost-effective production of alkaline-mannanase by alkaliphilic Bacillus sp. N16-5 isolated
previously from sediment of Wudunur Soda Lake in Inner
Mongolia, China. We used the sodium glutamate and
soymeal, which is a cheap by-product from the soy protein
industry, to replace the expensive nitrogen resources such
as peptone and yeast extract used in the previously works,
in the hope of improving the economics for the production
of alkaline -mannanase.
Materials and methods
Microorganism
Alkaliphilic Bacillus sp. N16-5, a producer of extracellular
alkaline -mannanases, was isolated previously from
sediment of Wudunur Soda Lake in Inner Mongolia, China
(Ma et al. 1991). The bacterium was maintained as a spore
stock or, for short periods of time, on nutrient agar slant.
Media
The seed medium contained (g l1): soluble starch 10,
peptone 10, yeast extract 5, NaCl 80, K2HPO4 1.5, MgSO40.3. Initial pH of the culture was adjusted to 7.58.0 before
sterilization at 121 C for 20 min, then 10 g l1 Na2CO3was added to adjust the pH to 9.510.0.
The basal fermentation medium used for alkaline -
mannanase production is the modified alkaline Horikoshi-II
medium (Horikoshi1971), which contained (g l1): konjac
mannan 12; soymeal 15 (provided by Genencor (Wuxi)
International, Inc.), contents (%, w/w): water 12, crude
protein 4447, crude fat 67, carbohydrate 1821, ash 56),
NaCl 80, sodium glutamate 1, yeast extract 5, K2HPO41.5,
and MgSO4 0.3. Initial pH of the culture was adjusted to
7.58.0 before sterilization at 121C for 20 min, then 10 g l1
Na2CO3 was added to adjust the pH 9.510.0.
The single-factor experiments design: prepared according
to Table1
The fermentation medium for the PB design was pre-
pared according to Tables 2 and 3, and the fermentation
medium for the RSM design was prepared according to
Tables4 and 5.
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Inoculum preparation and Shake flask experiments
Inoculum was prepared by transferring colonies from a
24-h slant culture into a 30-ml seed medium in a 250-ml
Erlenmeyer flask, and incubated at 37C for 24 h at
230 rpm. Each flask was then inoculated with 2% (v/v) of
24-h liquid culture. The culture was incubated at 37C at
230 rpm for 34 h. All experiments were repeated in
triplicate.
Enzyme production and activity assay
Enzyme centrifugation was done at a temperature below
4C. The centrifugal supernatant of the culture broth was
used as the enzyme source for the enzyme analysis. With
locust bean gum as the substrate, alkaline -mannanase
activity was assayed at 70C and pH 9.6 (0.05 mol l1 Gly-
NaOH buffer) by measuring the reducing sugars liberatedduring the hydrolysis of locust bean mannan, as described
previously. One unit of activity was defined as the amount
of enzyme catalyzing the production of 1 mol of the
reducing sugar per minute, using mannose as the standard
(Ma et al. 2004).
Batch fermentation in 5-l fermenter
The batch fermentation was carried out in 5-l fermenter
(Biotech-2001) equipped with three six-bladed disc impel-
ler, oxygen and pH electrodes, under the following
conditions: medium volume 3 l, inoculation volume 2%(v/v), temperature 37C, initial pH 9.510.0, aeration rate
1.0 vvm, and agitation speed 500 rpm. The fermentation
continued until the alkaline -mannanase activity reached
the highest values.
Experimental design
PluckettBurman design
PB design is one special type of a two-level fractional
factorial design basing on incomplete equilibrium piece
principle. It can pick up the main factors with the least
number of experiments from a list of candidate factors
(Plackett and Burman1946; Kalil et al. 2000).
The possible factors that affected the alkaline -
mannanase yield included konjac mannan, soymeal, NaCl,
sodium glutamate, yeast extract, K2HPO4, MgSO4, and
initial pH of medium. The 12-run PB design was used to
study these eight factors and dummy variables were used to
estimate the standard error during analysis of data. The
different variables were prepared in two levels, 1 for low
level and +1 for high level, and the high level was 1.5 times
of the low level, as shown in Table 2.
The steepest ascent experiment
The steepest ascent experiment can approach the largest
response area rapidly, determine the center point of the
central composite design (CCD) described further, and
ensure the validity and correctness of the response surface
analysis results. The first-order model equation obtained
from the PB test determined the ascent direction (or
descent, as required) and the length of ascent pace.
Table 1 Effect of different carbon and nitrogen sources on the
production of alkaline-mannanase from N16-5
Factors Concentration (g l1) Enzyme activity (U/ml)
Glucose 10 2.70.1
Mannose 10 2.20.1
Soluble starch 10 2.70.1
Konjac powder 10 122.84.2
12 167.36.1
15 153.25.2
Locust bean 10 105.33.7
12 143.64.6
15 151.24.9
Peptone 5 101.23.6
10 132.74.3
15 104.23.7
20 75.22.6
Yeast powder 10 64.52.1
15 93.03.1
20 117.14.3
30 87.42.6
Soymeal 10 89.72.715 144.74.3
20 112.73.7
30 93.22.9
Table 2 The factors, levels, and the regression analysis of the PB
design
Factors (g l1) Levels ttest P> |t|
1 +1
X1 pH 9.0 11.0 0.597373 0.592342
X2 NaCl 60.0 90.0 3.78336 0.032369*
X3 konjac mannan 10.0 15.0 0.0181 0.986694
X4 soybean meal 12.0 18.0 0.41635 0.705147
X5 yeast extract 4.0 6.0 0.19912 0.854897
X6 sodium glutamate 2.4 3.6 6.933144 0.006153**
X7 MgSO4 0.2 0.3 1.43007 0.248056
X8 K2HPO4 1.2 1.8 0.16292 0.880938
*Statistically significant at 95% of confidence level
**Statistically significant at 99% of confidence level
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Central composite design
Based on the results obtained from the PB design and the
steepest ascent experiment, the CCD was conducted to gain
the optimized levels of the main factors (Oh et al. 1995;
Wang et al. 2004). We can get a second-order empirical
model from the experimental data about the relationship
between the response value (alkaline -mannanase yield)
and the variables through polynomial regression analysis.
The form of the second-order polynomial model is:
Yb0X
biiXX
bijijX
bii2ii;
where Y is the predicted response, bi is the regression
coefficient, and xi is the coded value of the independent
variables. The relationship betweenxi and the natural value
of independent variable is:
xi Xi X0 =Xi;
whereXistands for the natural value of independent variable,X0 for the natural value of the independent variable at the
center point, and Xi is the step change value.
Software for experimental design and statistical analysis
Statistical Analysis System (SAS) Version 9.0 was used for
the experimental design and statistical analysis of the
experimental data. All of the optimization fermentation
experiments were conducted in triplicate, and the average
data of alkaline -mannanase yields were further analyzed
by the SAS 9.0. The quality of fit for the regression model
equation was expressed by the coefficient of determinationR2 and its statistical significance was determined by an F
test. The significance of the regression coefficients was
tested by a ttest (Heck et al. 2005b).
Results
The single-factor experiments
In our previous works, we found that the production of
alkaline -mannanase by strain N16-5 was induced by
addition of some substrates containing -mannan into the
medium (Ma et al.1991). The most suitable carbon source
was locust bean gum and the nitrogen sources were peptone
and yeast extract. But in the hope of improving the
economics for the production of alkaline -mannanase, we
used the cheaper substrates, such as konjac powder, soymeal,
and sodium glutamate to replace the locust bean gum,
peptone, and yeast extract. The results showed that all tested
concentrations of the konjac powder could induce the
alkaline-mannanase production, while at the concentration
Table 3 The experiments and results of the PB design
Run number Factor-coded levels Y alkaline -mannanase
yield (U/ml)X1 X2 X3 X4 X5 X6 X7 X8pH NaCl Konjac
mannan
Soybean
meal
Yeast extract Sodium
glutamate
MgSO4 K2HPO4
1 1 1 1 1 1 1 1 1 175.18.1
2 1 1 1 1 1 1 1 1 160.26.3
3 1 1 1 1 1 1 1 1 159.16.1
4 1 1 1 1 1 1 1 1 256.515.2
5 1 1 1 1 1 1 1 1 128.24.3
6 1 1 1 1 1 1 1 1 206.58.2
7 1 1 1 1 1 1 1 1 189.67.4
8 1 1 1 1 1 1 1 1 169.37.1
9 1 1 1 1 1 1 1 1 241.79.1
10 1 1 1 1 1 1 1 1 246.59.7
11 1 1 1 1 1 1 1 1 208.410.1
12 1 1 1 1 1 1 1 1 172.49.2
Table 4 The design and results of the steepest ascent experiment
Run NaCl
(g l1)
Sodium glutamate
(g l1)
Alkaline-mannanase
yield (U/ml)
1 100.0 2.4 128.15.4
2 95.0 2.6 189.38.1
3 90.0 2.8 263.211.5
4 85.0 3.0 307.215.3
5 80.0 3.2 254.410.3
6 75.0 3.4 237.29.5
7 70.0 3.6 190.56.3
8 65.0 3.8 204.18.6
9 60.0 4.0 220.39.5
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of 12 g l1, the enzyme activity (EA) reached the highest. In
the range of 1020 g l1, the soymeal could enhance the
enzyme production. In the concentration of 15 g l1, the EA
is the highest. Above this concentration, the EA decreased
(Table1).
Our previous experiments indicated that in addition to
soymeal, sodium glutamate was another nitrogen source for
effective production of alkaline -mannanase. We investi-gated the effects of various sodium glutamate concentra-
tions on the enzyme production; the results are shown in
Fig.1:the sodium glutamate really played an important role
in the production of the alkaline -mannanase. In the
concentration of 3 g l1
, the EA was 216.2 U/ml, which was
40% higher than that of the medium without sodium
glutamate.
NaCl plays a very important role in the alkaliphiles
physiology (Ma 1999). We also found that NaCl played a
very important role in the production of alkaline -
mannanase by alkaliphilic Bacillus sp.N16-5. The tolerant
concentration of NaCl is 150 g l1 for this strain (Ma et al.1991), while in the range of 80100 g l
1of NaCl, the EA
were comparatively high (Fig. 1). When the concentration
of NaCl was too high or too low, the enzyme production
sharply decreased.
Main factors for the production of alkaline -mannanase
The levels of the variables for the PB design were selected
according to the previous experiments. As shown in Table2,
the 12-run PB design was chosen to pick up the main
factors. The experiments and results of the PB design are
shown in Table3.
We can get the first-order regression equation by
regression analysis of the experimental data obtained from
the PB design.
Y192:41672:75X1 17:41667X2
0:08333X3 1:916667X4 0:916667
X5
31:91667X66:583333X7 0:75X8 1
This fit of the model was checked by R2, which was
calculated to be 95.59%, that is to say the regression equation
regressed well. According to the t-test results in Table2, we
can see NaCl and sodium glutamate are the two major factors
affecting the performance of the culture in terms of alkaline
-mannanase yields; the reliability values were 96.76 and
99.38%, respectively, at 95 and 99% confidence levels.
Optimization of the medium components for alkaline
-mannanase production
Validation of the central point for CCD
According to the results of the PB experiment, we can see
NaCl and sodium glutamate were the essential factors.
From the data shown in Table4, we can get the center point
of the subsequent experiment, which was NaCl 85.0 g l1,
sodium glutamate 3.0 g l1.
Optimization and analysis for the CCD design for alkaline
-mannanase production
The optimal concentration of medium components was
determined by CCD with the two variable NaCl and sodium
glutamate using the central point obtained from the steepest
ascent experiment. The level of konjac mannan, soymeal,
yeast extract, K2HPO4, MgSO4, and pH still remained the
original (konjac mannan 12, soymeal 15, yeast extract 5,
K2HPO4 1.5, MgSO4 0.3. pH 9.510.0). To make the
regression model accurate, repeat the center point five
times. The asterisk arm length =1.414. The experimental
design and results are in Table 5 and the statistical analysis
of data are shown in Table 6.
Regressing the data through SAS 9.0, we can get the
following quadratic empirical model:
Y2873:651611X19:510448X2
19:81252X1X14X1X2 18:06252
X2X2: 2
The analysis of variance was employed for the determi-
nation of significant parameters and to estimate the alkaline
-mannanase as a function of NaCl and sodium glutamate.
Data are shown in Table 6. The determining coefficientR2
0 20 40 60 80 100 1200
50
100
150
200
250-1 0 1 2 3 4 5
concentration of glutamine (g L-1)
EA(UmL-1)
concentration of NaCl (g L-1
)
Fig. 1 Effect of sodium glutamate and NaCl concentration on alkaline
-mannanase production. Sodium glutamate, NaCl
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was 98.29%, which indicated that this model congresses
well with the practice and can be used to analyze and
estimate alkaline -mannanase fermentation. Significance
of coefficients has been reported to be directly proportional
to t test and inversely to Pvalue (Heck et al. 2005b). The
smaller the P values, the bigger the significance of the
corresponding coefficient (Liu et al. 2003). In our work,
sodium glutamate, second-order NaCl, and second-order
sodium glutamate were highly significant, statistically
significant at 99% confidence level. The NaCl and the
interaction of the NaCl and sodium glutamate were also
very significant, and the reliability values were 97.51 and93.65% at 95% confidence level.
We can find the influences on the yield of the alkaline-
mannanase imposed by the factors and the reciprocity
between them directly in Fig. 2. The shapes of contour
curves showed that there were great effects on each other.
Maximal enzyme extraction was obtained at lower NaCl
and higher sodium glutamate concentration. From the
quadratic empirical model, we can get the models extreme
coordinate (0.120, 0.276), the corresponding NaCl
(84.40 g l1), sodium glutamate (3.11 g l1), and now
forecast the largest yield of the alkaline -mannanase for288.5 U/ml.
Validation of the models
The availability of the regression model (Eq. 2) of the
alkaline -mannanase by alkaliphilic Bacillus sp. N16-5
was tested using the calculated optimal culture composition
(g l1), viz. konjac mannan 12, soymeal 15, yeast extract 5,
NaCl 84.4, sodium glutamate 3.11, K2HPO4 1.5, MgSO40.3, Na2CO3 10, pH 9.510.0, with triplicate experiments.
The mean value of the alkaline -mannanase was
295.0 U/ml, which agreed well with the predicted value(288.5 U/ml). As a result, the models developed were
considered to be accurate and reliable for predicting the
production of alkaline -mannanase by alkaliphilic Bacil-
lus sp. N16-5.
Batch fermentation results
The feasibility of the regression models in a 5-l scaled
fermenter was also tested using the predicted optimal medium
composition (Fig. 3). With the optimal, maximum production
of alkaline -mannanase could reach 310.1 U/ml, which is
nearly twice compared with the original (167.1 U/ml). From
this, we can see this model can estimate the practical ferment
conditions correctly and improve the yield of alkaline -
mannanase effectively.
Discussion
Although previous research regarding alkaline -manna-
nase production has been reported, little information on the
Table 5 The experiment design and results of the CCD
Run number Coded factor values Y
X1 X2 Alkaline -
mannanase
yield (U/ml)
NaCl
(g l1)
Sodium glutamate
(g l1)
1 1 (80) 1 (2.6) 239.1 10.2
2 1 (80) 1 (3.4) 261.2 12.3
3 1 (90) 1 (2.6) 243.4 7.1
4 1 (90) 1 (3.4) 249.2 8.4
5 1.414 (78) 0 (3.0) 256.3 10.4
6 1.414 (92) 0 (3.0) 241.1 9.2
7 0 (85) 1.414 (2.4) 235.3 9.2
8 0 (85) 1.414 (3.6) 269.5 12.2
9 0 (85) 0 (3.0) 287.4 13.1
10 0 (85) 0 (3.0) 286.3 12.1
11 0 (85) 0 (3.0) 289.3 11.1
12 0 (85) 0 (3.0) 285.5 10.6
13 0 (85) 0 (3.0) 288.1 11.3
Table 6 Coefficient estimates by the regression model
Term SE t P>F
X1 1.284285 2.8433 0.024926*
X2 1.284285 7.405247 0.000149**
X1X1 1.377244 14.3856 0.0001**
X1X2 1.816252 2.20234 0.063512*
X2X2 1.377244 13.115 0.0001**
*Statistically significant at 95% of confidence level
** Statistically significant at 99% of confidence level
Fig. 2 Response surface plot for the effects of NaCl and sodium
glutamate on alkaline -mannanase production
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optimization of its production is available (Heck et al.
2005a). In this paper, we used the method of experimental
factorial design, and RSM design demonstrated that the
CCD and regression analysis methods were effective to find
the optimized NaCl and sodium glutamate concentrations
for the production of alkaline -mannanase from alkali-
philic Bacillus sp. N16-5, a newly isolated strain growing
on some economical and abundant substrate as konjac
mannan and soymeal replace the expensive carbon and
nitrogen resource, locust gum, peptone, and yeast extract.
As we know, NaCl plays a very important role in the
alkaliphiles physiology (Ma 1999). It can function as the
driving force of some endergonic processes in the cell
(Detkova and Pusheva 2006), so it can balance the
extracellular and intracellular pH of the cell, help the cell
produce energy, and is also very important in the substrate
transports (Ma 1999). The enzymes of such organisms
display maximum activity in the presence of salts and,
moreover, are inactivated in their absence. Our previous
experiments indicated that alkaliphilic Bacillus sp. N16-5
was also a salt-tolerant bacterium, but not so much
halophilic. When under high pH condition, around 9.510.0, the cell growth and the production of alkaline -
mannanase were comparatively desirable. But for the
effects of various NaCl concentrations on production of
alkaline -mannanase by strain N16-5, it was not so much
associated with the cell growth (data not shown). Around
the concentration of 80 g l1 NaCl, the production of
alkaline -mannanase is comparatively high. The lower
concentration of NaCl benefited cell growth, but not
enzyme production. While at higher concentration, NaCl
sharply decreased both cell growth and production of
alkaline -mannanase.
In our works, we added different amino acids to thesoymeal substrate and the sodium glutamate, and the alka-
line -mannanase activity increased greatly. With the RSM
analysis, we found that the maximum alkaline -manna-
nase activity was obtained at sodium glutamate concentra-
tion (3.11 g l1), and the activity was increased nearly twice
compared with the original medium. The amino acids and
their analogues have been known for their stimulatory
effect on the production of a number of enzymes such as -
amylase, glutamate oxaloacetate transaminase and gluta-
mate pyruvate transaminase, -galactosidase, and xylanases
(Ikura and Horikoshi1987). The effect of sodium glutamate
on the production of mannanase has been reported before
(Ma et al.1991), but the mechanism as to the -mannanase
stimulation has not been reported. It is possible that a
certain amino acid plays an important role at the start of the
regulative gene of the hydrolase (Levin and Forschiassin
1998). Gupta et al. (1999) demonstrated that the carbon
chain length and the position of CH3 and NH2 groups
have a significant role in the stimulation of production of
xylanase.
Statistical optimization method for fermentation process
could overcome the limitations of classic empirical methods
and was proved to be a powerful tool for the optimization
of the production of alkaline-mannanase from alkaliphilic
Bacillussp. N16-5. In this study, RSM model was proposed
to study the combined effects of culture media composi-
tions. Under optimal condition, the predicted production of
alkaline -mannanase was 288.5 U/ml by canonical
analysis. Validation experiments were also carried out to
verify the availability and the accuracy of the models, and
the results showed that the predict values agreed well with
the experimental values. The batch fermentation results in a
5-l fermenter also showed that optimized culture medium
Fig. 3 Time profile of fermentation in 5-l fermenter using the basal
medium (a) and the optimized medium (b) on the -mannanase
production from N16-5. pH, cell biomass (g l1), enzyme
activity (EA, U/ml)
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could improve the production of alkaline -mannanase
from alkaliphilic Bacillus sp. N16-5 in a large-scale
fermentation process. It strongly suggested that the produc-
tion of alkaline -mannanase by wild-strain alkaliphilic
Bacillus sp. N16-5 may be interesting for industrial
applications. The results of this study also provided useful
information for the optimization of medium composition
for the other extremozymes fermentation processes.
Acknowledgment This work was supported by grants of National
Basic Research Program of China (No.2007CB707804), National
High-Tech Program (No. 2006AA020104), Jiangsu Planned Projects
for Postdoctoral Research Funds (No.0601004A), and Program for
Changjiang Scholars and Innovative Research Team in University
(No. IRT0532). The authors would thank Dr. Luhong Tang for his
critical reading of this manuscript.
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