Optimization of a growth medium using a statistical approach for the production of an alkaline protease from a newly isolated Bacillus sp. L21

Optimization of Probiotic Lactobacilli Production for In-Feed Supplementation to Feedlot Cattle

The selection of probiotic bacteria based on their beneficial characteristics does not necessarily mean they can be later scaled up and used for technological applications and formula design. Three probiotic strains—Lactobacillus acidophilus CRL2074, Limosilactobacillus fermentum CRL2085, and Limosolactobacillus mucosae CRL2069, originally isolated from feedlot cattle feces—have demonstrated beneficial characteristics when used as in-feed probiotics. Therefore, the current study was conducted to develop a low-cost culture medium to optimize growth conditions to enhance biomass production. The study also sought to identify appropriate cryoprotective agents to sustain high functional cell numbers after freeze drying. A central composite design was applied to determine the optimal medium composition. This yielded a simplified, low-cost effective medium containing 3% molasses and industrial yeast extracts (0.5 to 2.5%) as carbon and nitrogen sources, which were added to a basal medium for each strain. Established production conditions at 37 °C, without agitation, and pH-controlled for the CRL2085 and CRL2069 strains, and free pH for the CRL2074 strain, allowed us to obtain biomass yields of 12.95, 18.20, and 12.25 g, respectively, at 24-h incubation, compared with the MRS medium. In addition, the cryoprotective effect of the selected agents was demonstrated to be strain-dependent. Thus, the highest viability (109–1010 CFU/g), stability during 30-d storage, and survival rate (88–99%) were achieved when 10% MSG (monosodium glutamate), sucrose + fructose + trehalose + WPC (whey protein concentrate) + 10% MSG, and 1.2% WPC + 10% trehalose, were used for freeze drying CRL2074, CRL2085, and CRL2069, respectively. Moreover, the probiotic strains retained their probiotic functionality when hydrophobic characteristics were evaluated. These results highlight the need to perform strain-specific evaluation of the critical factors involved in the large-scale production of probiotic lactobacilli to sustain viability and stability after the freeze drying and storage processes.

Effective multi-functional biotechnological applications of protease/keratinase enzyme produced by new Egyptian isolate (Laceyella sacchari YNDH)

BACKGROUND

Due to a multitude of industrial applications of keratinolytic proteases, their demands are increasing. The present investigation studied the production and monitoring of the most possible multi-functional applications of YNDH thermoalkaline keratin-degrading enzyme.

RESULTS

This work is considered the first that reported YNDH strain closely related to Laceyella sacchari strain; YNDH is a producer of protease/keratinase enzyme and able to degrade natural keratin such as feathers, wool, human hairs, and nails. Experimental design Plackett-Burman (PBD) was applied to evaluate culture conditions affecting the production of thermoalkaline protease/keratinase. Afterwards, Box-Behnken design (BBD) was applied to find out the optimum level of significant variables namely, NH₄Cl, yeast extract, and NaNO3 with a predicted activity of 1324.7 U/ml. Accordingly, the following medium composition and parameters were calculated to be optimum (%w/v): NH4Cl, 0.08; feather, 1; yeast extract, 0.04; MgSO₄.7H₂O, 0.02; NaNO₃, 0.016; KH₂PO₄, 0.01; K₂HPO_4, 0.01; pH, 8; inoculum size; 5%, cultivation temperature (Temp.) 45 °C and incubation time 48 h. The studied enzyme can degrade keratin-azure, remove proteinaceous materials, and is able to remove hairs from goat hides. These interesting characteristics make this enzyme a good candidate in many applications especially in detergent (Det.), in leather industries, and in pharmaceuticals particularly in nail treatment.

CONCLUSION

The promising properties of the newly keratin-degrading protease enzyme from Laceyella sacchari strain YNDH would underpin its efficient exploitation in several industries to cope with the demands of worldwide enzyme markets.

An Alkaline Protease from Bacillus pumilus MP 27: Functional Analysis of Its Binding Model toward Its Applications As Detergent Additive

A proteolytic strain of Bacillus pumilus MP 27 was isolated from water samples of Southern ocean produced alkaline protease. Since protease production need expensive ingredients, an economically viable process was developed by using low cost carbon source, wheat straw, supplemented with peptone. This protease was active within temperature ranges 10–70°C at pH 9. This process was optimized by response surface methodology using a Box Bekhman design by Design Expert 7.0 software that increased the protease activity to 776.5 U/ml. Moreover, the enzyme was extremely stable at a broad range of temperature and pH retaining 69% of its activity at 50°C and 70% at pH 11. The enzyme exhibited excellent compatibility with surfactants and commercial detergents, showing 87% stability with triton X-100 and 100% stability with Tide commercial detergent. The results of the wash performance analysis demonstrated considerably good de-staining at 50 and 4°C with low supplementation (109 U/ml). Molecular modeling of the protease revealed the presence of serine proteases, subtilase family and serine active site and further docking supported the association of catalytic site with the various substrates. Certainly, such protease can be considered as a good detergent additive in detergent industry with a possibility to remove the stains effectively even in a cold wash.

Approach toward enhancement of halophilic protease production by Halobacterium sp. strain LBU50301 using statistical design response surface methodology

•

Halophilic protease producing Halobacterium sp. strain LBU50301 was isolated.

•

RSM optimized the fermentation conditions to enhance halophilic protease yield.

•

Optimized conditions used in bioreactor resulted about 13-fold enhancement.

A new potent halophilic protease producer, Halobacterium sp. strain LBU50301 was isolated from salt-fermented fish samples (budu) and identified by phenotypic analysis, and 16S rDNA gene sequencing. Thereafter, sequential statistical strategy was used to optimize halophilic protease production from Halobacterium sp. strain LBU50301 by shake-flask fermentation. The classical one-factor-at-a-time (OFAT) approach determined gelatin was the best nitrogen source. Based on Plackett–Burman (PB) experimental design; gelatin, MgSO₄·7H₂O, NaCl and pH significantly influenced the halophilic protease production. Central composite design (CCD) determined the optimum level of medium components. Subsequently, an 8.78-fold increase in corresponding halophilic protease yield (156.22 U/mL) was obtained, compared with that produced in the original medium (17.80 U/mL). Validation experiments proved the adequacy and accuracy of model, and the results showed the predicted value agreed well with the experimental values. An overall 13-fold increase in halophilic protease yield was achieved using a 3 L laboratory fermenter and optimized medium (231.33 U/mL).

Enhanced production of extracellular proteolytic enzyme excreted by a newly isolated Bacillus subtilis FBL-1 through combined utilization of statistical designs and response surface methodology

Protease production by newly isolated B. subtilis FBL-1 was optimized and enhanced by combined utilization of three statistical experimental designs.

Optimizing Production of Two Potential Probiotic Lactobacilli Strains Isolated from Piglet Feces as Feed Additives for Weaned Piglets

Two probiotic strains, Lactobacillus johnsonii x-1d-2 and Lactobacillus mucosae x-4w-1, originally isolated from piglet feces, have been demonstrated to possess antimicrobial activities, antibiotic resistances and interleukin-6 induction ability in RAW 267.4 macrophages in our previous study. These characteristics make L. johnsonii x-1d-2 and L. mucosae x-4w-1 good candidates for application in feed probiotics. In this study, soybeal meal, molasses and sodium acetate were selected to optimize the growth medium for cultivation of L. johnsonii x-1d-2 and L. mucosae x-4w-1. These two strains were then freeze-dried and mixed into the basal diet to feed the weaned piglets. The effects of L. johnsonii x-1d-2 and L. mucosae x-4w-1 on the growth performance and fecal microflora of weaned piglets were investigated. The results showed that the bacterial numbers of L. johnsonii x-1d-2 and L. mucosae x-4w-1 reached a maximum of 8.90 and 9.30 log CFU/mL, respectively, when growing in optimal medium consisting of 5.5% (wt/vol) soybean meal, 1.0% (wt/vol) molasses and 1.0% (wt/vol) sodium acetate. The medium cost was 96% lower than the commercial de Man, Rogosa and Sharpe medium. In a further feeding study, the weaned piglets fed basal diet supplemented with freeze-dried probiotic cultures exhibited higher (p<0.05) body weight gain, feed intake, and gain/feed ratio than weaned piglets fed basal diet. Probiotic feeding also increased the numbers of lactobacilli and decreased the numbers of E. coli in the feces of weaned piglets. This study demonstrates that L. johnsonii x-1d-2 and L. mucosae x-4w-1 have high potential to be used as feed additives in the pig industry.

Utilization of different waste proteins to create a novel PGPR-containing bio-organic fertilizer

High-quality bio-organic fertilizers (BIOs) cannot be produced without the addition of some proteins, while many waste proteins are haphazardly disposed, causing serious environmental pollution. In this study, several waste proteins were used as additives to assist with the reproduction of the functional microbe (Bacillus amyloliquefaciens SQR9) inoculated into matured composts to produce BIOs. An optimized composition of solid-state fermentation (SSF) raw materials was predicted by response surface methodology and experimental validation. The results showed that 7.61% (w/w, DW, the same below) rapeseed meal, 8.85% expanded feather meal, 6.47% dewatered blue algal sludge and 77.07% chicken compost resulted in maximum biomass of strain SQR-9 and the maximum amount of lipopeptides 7 days after SSF. Spectroscopy experiments showed that the inner material structural changes in the novel SSF differed from the control and the novel BIO had higher dissolved organic matter. This study offers a high value-added utilization of waste proteins for producing economical but high-quality BIO.

Production of a water-soluble fertilizer containing amino acids by solid-state fermentation of soybean meal and evaluation of its efficacy on the rapeseed growth

Soybean meal is a by-product of soybean oil extraction and contains approximately 44% protein. We performed solid-state fermentation by using Bacillus subtilis strain N-2 to produce a water-soluble fertilizer containing amino acids. Strain N-2 produced a high yield of protease, which transformed the proteins in soybean meal into peptide and free amino acids that were dissolved in the fermentation products. Based on the Plackett-Burman design, the initial pH of the fermentation substrate, number of days of fermentation, and the ratio of liquid to soybean meal exhibited significant effects on the recovery of proteins in the resulting water-soluble solution. According to the predicted results of the central composite design, the highest recovery of soluble proteins (99.072%) was achieved at the optimum conditions. Under these conditions, the resulting solution contained 50.42% small peptides and 7.9% poly-γ-glutamic acid (γ-PGA). The water-soluble fertilizer robustly increased the activity of the rapeseed root system, chlorophyll content, leaf area, shoot dry weight, root length, and root weight at a concentration of 0.25% (w/v). This methodology offers a value-added use of soybean meal.

Statistical optimization of alkaline protease production from brackish environment Bacillus sp. SKK11 by SSF using horse gram husk

Protease production by Bacillus sp. SKK11 isolated from brackish environment was studied by solid-state fermentation with horse gram husk. Response surface methodology-based Box-Behnken design (BBD) was used to optimize the variables such as pH, maltose, and MgSO₄. The BBD design analysis showed a reasonable adjustment of the quadratic model with the experimental data. Statistics-based contour and three-dimensional (3-D) plots were generated to evaluate the changes in the response surface and to understand the relationship between the enzyme yield and the culture conditions. The maximum yield of the enzyme was observed at pH 9.0.

Biodegradation of shrimp biowaste by marine Exiguobacterium sp. CFR26M and concomitant production of extracellular protease and antioxidant materials: production and process optimization by response surface methodology

Twelve marine bacterial cultures were screened for extracellular protease activity, and the bacterium CFR26M which exhibited the highest activity on caseinate agar plate was identified as an Exiguobacterium sp. Significant amount of extracellular protease (5.9 ± 0.3 U/ml) and antioxidant materials, measured as 2,2'-diphenyl picrylhydrazyl (DPPH) radical scavenging activity (44.4 ± 0.5 %), was produced by CFR26M in submerged fermentation using a shrimp biowaste medium. Response surface methodology (RSM) was employed to optimize the process variables for maximum production of protease and antioxidant materials by CFR26M. Among the seven variables screened by two-level 2**(7-2) fractional factorial design, the concentration of shrimp biowaste, sugar, and phosphate was found to be significant (p ≤ 0.05). The optimum levels of these variables were determined by employing the central composite design (CCD) of RSM. The coefficient of determination (R (2)) values of 0.9039 and 0.8924 for protease and antioxidant, respectively, indicates the accuracy of the CCD models. The optimum levels of shrimp biowaste, sugar, and phosphate were 21.2, 10.5, and 2.3 % (w/v) for production of protease and 28.8, 12, and 0.32 % (w/v) for production of antioxidant material, respectively. The concentration of shrimp biowaste, sugar, and phosphate had linear and quadratic effect on both protease and antioxidant productions. RSM optimization yielded 6.3-fold increases in protease activity and 1.6-fold in antioxidant material production. The crude protease of CFR26M had a maximum activity at 32 ± 2 °C with pH 7.6. This is the first report on the use of marine Exiguobacterium sp. for concomitant production of protease and antioxidant materials from shrimp biowaste.

Administration of Bacillus subtilis strains in the rearing water enhances the water quality, growth performance, immune response, and resistance against Vibrio harveyi infection in juvenile white shrimp, Litopenaeus vannamei

In this study, vegetative cell suspensions of two Bacillus subtilis strains, L10 and G1 in equal proportions, was administered at two different doses 10(5) (BM5) and 10(8) (BM8) CFU ml(-1) in the rearing water of shrimp (Litopenaeus vannamei) for eight weeks. Both probiotic groups showed a significant reduction of ammonia, nitrite and nitrate ions under in vitro and in vivo conditions. In comparison to untreated control group, final weight, weight gain, specific growth rate (SGR), food conversion ratio (FCR) and digestive enzymatic activity were significantly greater in the BM5 and BM8 groups. Significant differences for survival were recorded in the BM8 group as compared to the control. Eight weeks after the start of experiment, shrimp were challenged with Vibrio harveyi. Statistical analysis revealed significant differences in shrimp survival between probiotic and control groups. Cumulative mortality of the control group was 80%, whereas cumulative mortality of the shrimp that had been given probiotics was 36.7% with MB8 and 50% with MB5. Subsequently, real-time RT-PCR was employed to determine the mRNA levels of prophenoloxidase (proPO), peroxinectin (PE), lipopolysaccharide- and β-1,3-glucan- binding protein (LGBP) and serine protein (SP). The expression of all immune-related genes studied was only significantly up-regulated in the BM5 group compared to the BM8 and control groups. These results suggest that administration of B. subtilis strains in the rearing water confers beneficial effects for shrimp aquaculture, considering water quality, growth performance, digestive enzymatic activity, immune response and disease resistance.

Characterization of acidic protease from Aspergillus niger BCRC 32720

An acid protease from the broth of a 24 h cultivated Aspergillus niger BCRC 32720 was purified to electrophoretical homogeneity by CM Sepharose FF and Sephacryl S-100 HR chromatographs. The specific activity, purification fold, and yield were 23.29 kU/mg, 2.5, and 24.2%, respectively. Molecular mass (M) and N-terminal amino acid sequence were 47.5 kDa and SKGSAVTT, whereas the pH and temperature optima were at 2.5 and 50 °C, respectively. It was stable at pH 2.0-4.0 or ≤40 °C and activated by Fe(2+) and cysteine, but partially inhibited by phenylmethanesulfonyl fluoride and tosyllysine chloromethyl ketone and highly inhibited by Ag(+), Sn(2+), Fe(3+), Sb(3+), and pepstatin A. It was considered to be an aspartic protease.

Production of lipopeptides by Bacillus amyloliquefaciens XZ-173 in solid state fermentation using soybean flour and rice straw as the substrate

This work was aimed to produce lipopeptides by Bacillus amyloliquefaciens XZ-173 in solid state fermentation using agro-industrial byproducts. A central composite design was used to get the highest lipopeptides production. Results revealed that the optimal conditions for maximum lipopeptides production were 1.79% starch and 1.91% yeast extract by employing 5.58 g soybean flour and 3.67 g rice straw as the solid substrate with initial pH 7.5, moisture content 55% and a 10% inoculum level at 30°C for 2 days. Under these conditions, the experimental yield of lipopeptides reached 50.01 mg/gds, which was very close to the predicted value (49.91 mg/gds). At high concentration, the lipopeptides extracted from fermented substrates showed strong antibiotic activity against Rhizoctonia solani and Ralstonia solanacearum and certain emulsification but good emulsion stability. This is the first report on lipopeptides production that uses rice straw as a major substrate.

Optimization of acid protease production by Aspergillus niger I1 on shrimp peptone using statistical experimental design

Medium composition and culture conditions for the acid protease production by Aspergillus niger I1 were optimized by response surface methodology (RSM). A significant influence of temperature, KH(2)PO(4), and initial pH on the protease production was evaluated by Plackett-Burman design (PBD). These factors were further optimized using Box-Behnken design and RSM. Under the proposed optimized conditions, the experimental protease production (183.13 U mL(-1)) closely matched the yield predicted by the statistical model (172.57 U mL(-1)) with R(2) = 0.914. Compared with the initial M1 medium on which protease production was 43.13 U mL(-1), a successful and significant improvement by 4.25 folds was achieved in the optimized medium containing (g/L): hulled grain of wheat (HGW) 5.0; KH(2)PO(4) 1.0; NaCl 0.3; MgSO(4)(7H(2)O) 0.5; CaCl(2) (7H(2)O) 0.4; ZnSO(4) 0.1; Na(2)HPO(4) 1.6; shrimp peptone (SP) 1.0. The pH was adjusted at 5 and the temperature at 30°C. More interestingly, the optimization was accomplished using two cheap and local fermentation substrates, HGW and SP, which may result in a significant reduction in the cost of medium constituents.

Optimization of 2,3-dihydroxybiphenyl 1,2-dioxygenase expression and its application for biosensor

In this study, two statistical experimental designs, Plackett-Burman design (PBD) and response surface methodology (RSM), were employed to enhance the expression of 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC_LA-4), which was subsequently used for the construction of catechol biosensor. Ten important factors were evaluated by PBD, and four significant parameters were then optimized by RSM. Under the favorable fermentation conditions, the maximal specific activity of BphC_LA-4 was about 0.58U/mg with catechol as substrate. Meanwhile, homology modeling and molecular docking were utilized to help understand the interaction between BphC_LA-4 and catecholic substrates, which illustrated that BphC_LA-4 presented lower binding affinity towards 4-methylcatechol in comparison with 3-methylcatechol and catechol. Interestingly, the BphC_LA-4 enzyme electrode prepared by SiO2 sol-gel showed good response to all these three catecholic compounds. The differences of selectivity to 4-methylcatechol between free and immobilized enzyme implied that the introduction of electro-catalysis might have an effect on the enzyme-catalysis process.

Optimization of the production of organic solvent-stable protease by Bacillus sphaericus DS11 with response surface methodology

Response surface methodology (RSM) was employed to enhance the production of organic solvent-stable protease by Bacillus sphaericus DS11. A significant influence of glycerol, MgSO₄·7H₂O, and pH on organic solvent-stable protease production was noted with Plackett-Burman design. Then, a three-level Box-Behnken design was employed to optimize the medium composition and culture conditions for the production of the protease in shake-flask. Using this methodology, the quadratic regression model of producing organic solvent-stable protease was built and the optimal combinations of media constituents and culture conditions for maximum protease production were determined as glycerol 12.47 g/L, MgSO₄·7H₂O 0.73 g/L, and pH 8.25. Protease production obtained experimentally coincident with the predicted value and the model was proven to be adequate. The enhancement of protease from 465.06 U/mL to 1182.68 U/mL was achieved with the optimization procedure.

Low-cost fermentation medium for alkaline protease production by Bacillus mojavensis A21 using hulled grain of wheat and sardinella peptone

Media composition and culture conditions for surfactant stable alkaline protease production by Bacillus mojavensis A21 were optimized using two statistical methods. Plackett-Burman design was applied to find the optimal ingredients and conditions to improve yields. Response surface methodology (RSM), including central composite design, was used to determine the optimal concentrations and conditions. The results indicated that several components, including hulled grain of wheat (HGW), sardinella peptone (SP), NaCl, CaCl(2), MgSO(4), K(2)HPO(4), KH(2)PO(4), agitation, culture temperature and initial medium pH, had significant effects on production. The statistical model was constructed via central composite design (CCD) using four selected variables (HGW, NaCl, KH(2)PO(4) and K(2)HPO(4)). Under the proposed optimized conditions, the protease experimental yield (1860.63U/mL) closely matched the yield predicted by the statistical model (1838.60U/mL) with R(2)=0.98. An overall 14.0-fold increase in protease production was achieved using the optimized medium (HGW 30.0g/L, SP 1.0g/L, NaCl 2.0g/L, KH(2)PO(4) 1.0g/L, K(2)HPO(4) 0.3g/L, CaCl(2) 2.0g/L, MgSO(4) 1.0g/L and pH 9.0, compared with the unoptimized basal medium (starch 10.0g/L, yeast extract 2.0g/L, KH(2)PO(4) 0.1g/L, K(2)HPO(4) 0.1g/L, CaCl(2) 0.5g/L and pH 8.0; 137U/mL). A successful and significant improvement (14-fold) in the production of protease by the A21 strain was accomplished using cheap carbon and nitrogen substrates (HGW and SP), which may result in a significant reduction in the cost of medium constituents.

Modeling and optimization of phenylalanine ammonia lyase stabilization in recombinant Escherichia coli for the continuous synthesis of l-phenylalanine on the statistical-based experimental designs

Some approaches for improving recombinant phenylalanine ammonia lyase (PAL) stability in Escherichia coli during the enzymatic methods of l-phenylalanine (l-Phe) production were developed following preliminary studies by means of statistical-based experiment designs (response surface method). The traditional non-statistical technology was used to screen four critical factors for PAL stability during the bioconversion process, viz., glycerin, sucrose, 1,4-dithiothreitol (DTT), and MgSO(4). The central composite design (CCD) was applied to optimize the combined effect of critical factors for recombinant PAL stability and understand the relationship between the factors and PAL stability. The optimum values for testing variables were 13.04 mM glycerin, 1.87 mM sucrose, 4.09 mM DTT, and 69 mM Mg(2+). A second-order model equation was suggested and then validated experimentally. The model adequacy was very satisfactory because the coefficient of determination was 0.88. The maximum PAL activity was retained as 67.73 units/g after three successive cycles of bioconversion. In comparison to initial PAL activity, the loss of PAL activity was only 22%. PAL activity was enhanced about 23% in comparison to the control (without any stabilizer additives). PAL stability was significantly improved during successive bioconversion. The results obtained here verified the effectiveness of the applied methodology and may be helpful for l-Phe production on an industrial scale.

Acid protease production by solid-state fermentation using Aspergillus oryzae MTCC 5341: optimization of process parameters

Aspergillus oryzae MTCC 5341, when grown on wheat bran as substrate, produces several extracellular acid proteases. Production of the major acid protease (constituting 34% of the total) by solid-state fermentation is optimized. Optimum operating conditions obtained are determined as pH 5, temperature of incubation of 30 degrees C, defatted soy flour addition of 4%, and fermentation time of 120 h, resulting in acid protease production of 8.64 x 10(5) U/g bran. Response-surface methodology is used to generate a predictive model of the combined effects of independent variables such as, pH, temperature, defatted soy flour addition, and fermentation time. The statistical design indicates that all four independent variables have significant effects on acid protease production. Optimum factor levels are pH 5.4, incubation temperature of 31 degrees C, 4.4% defatted soy flour addition, and fermentation time of 123 h to yield a maximum activity of 8.93 x 10(5) U/g bran. Evaluation experiments, carried out to verify the predictions, reveal that A. oryzae produces 8.47 x 10(5) U/g bran, which corresponds to 94.8% of the predicted value. This is the highest acid protease activity reported so far, wherein the fungus produces four times higher activity than previously reported [J Bacteriol 130(1): 48-56, 1977].

Improvement in the growth performance of white shrimp, Litopenaeus vannamei, by a protease-producing probiotic, Bacillus subtilis E20, from natto

AIMS

To isolate and identify a benefic bacterium, Bacillus subtilis E20, from natto (fermented soybeans), and incorporate it into shrimp feed to promote shrimp growth performance.

METHODS AND RESULTS

A protease-producing bacterium, E20, isolated from natto was identified as B. subtilis by an API 50 CHB kit and the 16S rDNA sequence. B. subtilis E20 was able to grow at a broad range of temperatures (10-50 degrees C), pH values (5-10), and NaCl levels (0-9%). The best culture conditions for B. subtilis E20 to produce the protease were 40 degrees C, a pH of 6-8 and 0% NaCl. No shrimp died after being injected with B. subtilis E20 [up to 10(9) colony-forming units (CFU) per shrimp]. Bacillus subtilis E20 was incorporated in diets at the levels of 0 (control), 10(6), 10(7), and 10(8) CFU kg(-1) for shrimp grow-out culture, and results showed that after feeding on B. subtilis E20-containing diets (10(8) CFU kg(-1) of diet), shrimp had excellent growth performance and production compared to the control because protease activities in the digestive tract were improved by B. subtilis E20.

CONCLUSIONS

Bacillus subtilis E20 isolated from natto is a great protease producer and is able to improve shrimp growth performance through increasing the digestibility of food.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results suggest that B. subtilis E20 is a potential candidate for use as a probiotic to improve shrimp growth performance, and consequently reduce feed costs.

Screening and optimization of nutritional factors for higher dextransucrase production by Leuconostocmesenteroides NRRL B-640 using statistical approach

To improve dextransucrase production from Leuconostocmesenteroides NRRL B-640 culture medium was screened and optimized using the statistical design techniques of Plackett-Burman and response surface methodology (RSM). Plackett-Burman design with six variables viz. sucrose, yeast extract, K2HPO4, peptone, beef extract and Tween 80 was performed to screen the nutrients that were significantly affecting dextransucrase production. The variables sucrose, K2HPO4, yeast extract and beef extract showed above 90% confidence levels for dextransucrase production and were considered as significant factors for optimization using response surface methodology. 2(4)-central composite design was used for RSM optimization. The experimental results were fitted to a second-order polynomial model which gave a coefficient of determination R2=0.95. The optimized composition of 30g/l sucrose, 18.9g/l yeast extract, 19.4g/l K2HPO4 and 15g/l beef extract gave an experimental value of dextransucrase activity of 10.7U/ml which corresponded well with the predicted value of 10.9U/ml by the model.

Enhanced production of exocellular glucansucrase from Leuconostoc dextranicum NRRL B-1146 using response surface method

Statistically-based experimental designs were applied to optimize the fermentation for the production of glucosyltransferase by Leuconostoc dextranicum NRRL B-1146. Eleven medium components were examined for their significance on enzyme production using Plackett-Burman factorial design. Tween 80, sucrose and K2HPO4 significantly improved the enzyme production process. The combined effect of these nutrients on glucansucrase production were studied using a 2 2 full-factorial central composite design, a second-order polynomial was established to identify the relationship between the enzyme output and the three medium components. The optimal concentration of variables for maximum glucansucrase production were Tween 80 (0.55%, v/v); sucrose (5.6%, w/v) and K2HPO4 (1%, w/v). The maximum enzyme activity by predicted model was 6.53 U/ml that was in perfect agreement with the actual experimental value (6.40 U/ml).