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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.

    1016 Appl Microbiol Biotechnol (2007) 75:10151022

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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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