Utilization of Agro-industrial Residues for Poly(3-hydroxyalkanoate) Production by <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> 42A2 (NCIMB 40045): Optimization of Culture Medium

In this study, central composite design and a response surface methodology are shown to be useful tools for medium optimization, in cultures of Pseudomonas aeruginosa 42A2 using an industrial oil byproduct, for polyhydroxyalkanoate (PHA) production. The optimum medium composition for PHA production includes: 80 g/L of the carbon source; 18.2 g/L of NaNO₃ and 3.3 g/L of K₂HPO₄/1.6 g/L KH₂PO₄ (R ² = 0.989). The models were validated experimentally by cultivating Pseudomonas aeruginosa 42A2 in optimum media that yielded similar biomass (18.73 g/L) and PHA (4.63 g/L) concentrations to the predicted values. The optimized media showed an increase in biomass productivity from 0.06 to 0.39 g biomass/L h, and an increase in PHA productivity from 0.03 to 0.1 g PHA/L h.     

High-Performance Production of Biosurfactant Rhamnolipid with Nitrogen Feeding

Nitrate is one of the most important factors for fermentative production of rhamnolipid, while it has not yet been conclusively demonstrated that nitrogen limitation or abundance is beneficial for improvement of rhamnolipid production. This study clarified that high concentration of NaNO₃ is conducive for high-performance production of rhamnolipid. An optimum rhamnolipid yield was achieved by 43.3 g L⁻¹ with an initial concentration of NaNO₃ equal to 10 g L⁻¹ during the regular fed-batch fermentation process by Pseudomonas aeruginosa ATCC 9027. Additionally, this rhamnolipid production was further improved to 61.2 g L⁻¹, which was two folds higher than that value obtained during batch fermentation, when the NaNO₃ concentration was maintained about 5 g L⁻¹. Furthermore, specific volume productivity of rhamnolipid was improved by over 30% in the presence of NaNO₃ at concentration ranging from 5 to 6 g L⁻¹ during sequential fed-batch fermentation, resulting a high value of 0.4 and 0.59 g L⁻¹ h⁻¹ within one batch of sequential fed-batch fermentation for a period of 17 days by P. aeruginosa ATCC 9027 and PAO1, respectively. It seems that sustaining high-concentration NaNO₃ during fed-batch fermentation is advantageous for high-performance production of rhamnolipid.     

Sequential optimization of culture medium composition for extracellular lipase production by Bacillus sphaericus using statistical methods

A sequential optimization strategy with the aid of statistical design of experiments was used to enhance the lipase (triacylglycerol acylhydrolases, EC 3.1.1.3) production by Bacillus sphaericus in submerged cultivation. A Plackett–Burman experimental design was used to evaluate the twelve medium components. Various vegetable oil inducers were tested for lipase production in the second step and the third step was to identify the optimal values of the significant medium components with sesame oil as the inducer using response surface methodology. A predictive model of the combined effects of the independent variables using response surface methodology and an artificial neural network was proposed. Unstructured kinetic models, a logistic model and a Luedeking–Piret model, were used to describe the cell mass and lipase production respectively. The significant variables affecting lipase production were found to be glucose, olive oil, peptone, NaCl and MnSO₄.H₂O. Sesame oil was found to be the best inducer for lipase production by Bacillus sphaericus. The maximum lipase activity of 4.45 U mL^?1, which was 1.5 times the maximum activity obtained in the Plackett–Burman experimental trials, was obtained at the optimum combination of medium constituents containing 12.695 g L^?1 glucose, 13.161 mL L^?1 sesame oil, 9.947 g L^?1 peptone, 3.25 g L^?1 NaCl, 0.5917 g L^?1 MnSO₄.H₂O and other insignificant components at the fixed level. The statistical design of experiments offers an efficient methodology to identify the significant variables and to optimize the factors with a minimum number of experiments for lipase production by Bacillus sphaericus. Copyright © 2007 Society of Chemical Industry     

Biodiesel production from Stichococcus strains at laboratory scale

BACKGROUND: This paper reports the results of an experimental campaign of autotrophic cultures of Stichococcus strains aiming at selecting the most promising strain for biofuel production. The strain selected—S. bacillaris 158/11—was cultivated in 1 L lab‐scale bubble column photobioreactors under fed‐batch and semi‐continuous conditions. A Bold basal medium supplemented with NaNO₃ as nitrogen source was adopted. Tests were carried out at 23 °C, 140 µE m^?2 s^?1, and air flow rate ranging between 0.4 and 4 vvm. Cultures were characterized in terms of pH, concentration of total nitrogen, total organic carbon, total inorganic carbon, biomass, lipid fraction and methyl‐ester distribution of transesterified lipids. RESULTS: S. bacillaris 158/11 proved to be the best strain to produce biodiesel. Methyl‐ester distribution was characterized by a large fraction of methyl palmitate, methyl linolenate, methyl linoleate, and methyl oleate along with phytol. The process photosynthetic efficiency—fraction of available light stored as chemical energy ‐ was about 1.5%. Specific biomass productivity was ～60 mg_DM L^?1 day^?1 under the semi‐continuous conditions tested. Total lipid productivity was 14 mg L^?1 day^?1 at a dilution rate of 0.050 L day^?1. CONCLUSION: S. bacillaris 158/11 is a potential strain for massive microalgae cultures for biofuel production. Higher biomass/total‐lipid productivity could be obtained in sunlight. Copyright © 2011 Society of Chemical Industry     

Biogas Plant Upgrade to CO2-Free Technology: A Techno-Economic Case Study

A techno-economic analysis was performed for a biogas plant with in-built algae production. Degradation in the fermenter occurs under mesophilic conditions, to produce 605 Nm³t⁻¹_TS of biogas and 343 Nm³t⁻¹_TS of methane after 50 days. The biogas was combusted in a combined heat-and-power unit to produce heat and electricity. Cultivation of Chlorella vulgaris was done in co-annular photo-bioreactors, with an annual productivity of 107.5 t. For cultivation, both autotrophic and mixotrophic growth were assumed. Detailed mass and energy balances were done. For both conditions of algae growth, the results are approximately the same after a 30-year payback period.     

Evaluation and optimization of food-grade tannin acyl hydrolase production by a probiotic Lactobacillus plantarum strain in submerged and solid state fermentation

Tannin acyl hydrolase (tannase) production by Lactobacillus plantarum MTCC1407 was studied in submerged and solid-state fermentation process. Sequential optimization strategy using Plackett–Burman screening and response surface methodology was adopted to optimize the submerged fermentation process. Eight medium components were evaluated initially by Plackett–Burman two level factorial designs to identify the most significant parameters that affect the tannase production. The significant variables affecting tannase production were found to be tannic acid, glucose and MnSO₄·7H₂O. These factors were further optimized by response surface methodology. Maximum tannase activity of 9.13 U ml^?1 was observed at 30 h using the following medium composition (g l^?1): tannic acid, 13.16; glucose, 1.5; NH₄Cl, 1.0; CaCl₂·2H₂O, 1.0; K₂HPO₄, 0.5; KH₂PO₄, 0.5; MgSO4·7H₂O, 0.5 and MnSO₄·7H₂O, 0.03. Among the various carbon sources examined for tannase production by L. plantarum, glucose and tannic acid combination was found to be decisive for enhancing tannase yield. Solid state fermentation was conducted using various solid substrates and agricultural residues. Maximum tannase activity of 5.319 U gds^?1 was obtained using coffee husk as substrate.     

Production of poly‐3‐hydroxybutyrate by Cupriavidus necator from corn syrup: statistical modeling and optimization of biomass yield and volumetric productivity

BACKGROUND: The paper reports an investigation into the possibility of producing poly‐3‐hydroxybutyrate (P(3HB)) polyester using corn syrup, a relatively low cost by‐product from the starch industries. The concentrations of medium components, corn syrup, dipotassium hydrogen phosphate (K₂HPO₄), sodium dihydrogen phosphate (NaH₂PO₄) and ammonium sulfate [(NH₄)₂SO₄] were optimized using design of experiments (DOE). RESULTS: Response surface methodology (RSM) under central composite face design (CCFD) was used to obtain the optimum values of medium components and responses in terms of biomass yield and volumetric P(3HB) productivity. The highest P(3HB) productivity and biomass yield obtained were 0.224 g L^?1 h^?1 and 0.57 g g^?1, respectively. A limited‐nitrogen concentration had a higher volumetric P(3HB) productivity (0.170 g L^?1 h^?1) than that of the excess nitrogen batch experiment (0.0675 g L^?1 h^?1). The optimum corn syrup:N:P ratio of 50:0.078:1 was based on numerical optimization of the desirability function between biomass yield and volumetric P(3HB) productivity by Cupriavidus necator DSMZ 545. CONCLUSION: The results obtained in this study demonstrated that P(3HB) could be efficiently produced to a high concentration with high productivity by applying nitrogen limitation in a defined medium, indicating this agricultural by‐product to be a suitable nutrient source in further studies to develop biomaterials through biotechnology. Copyright © 2010 Society of Chemical Industry     

Optimization and Characterization of Biosurfactant Rhamnolipid Production by Pseudomonas aeruginosa Isolated from an Artificially Contaminated Soil

Biosurfactants are surfactants biologically produced by microorganisms, presenting several advantages when compared to synthetic surfactants. Pseudomonas aeruginosa is known for producing rhamnolipids, considered one of the most interesting types of biosurfactants due to their high yields, when compared to other types. In this work, the production of rhamnolipid from P. aeruginosa was optimized. At first, the Plackett–Burman design was used to select most significant variables affecting the biosurfactant production yield among nine variables—carbon–nitrogen ratio, carbon concentration, nitrogen source, pH, cultivation time, potassium and magnesium concentrations, agitation, and temperature. Then, using main variables, a central point experimental design aiming to optimize rhamnolipid production was performed. The maximum biosurfactant concentration obtained was 0.877 mg L⁻¹. The rhamnolipid also displayed a great emulsification rate, reaching approximately 67%, and the ability to reduce water surface tension from 72.02 to 35.26 mN m⁻¹ at a critical micelle concentration (CMC) of 127 mg L⁻¹, in addition to presenting a good stability when exposed to wide pH and salinity ranges. The results suggest that rhamnolipids are promising substitutes for synthetic surfactants, especially due to lower impacts on the environment.     

Effect of electrolyte concentration on the properties of the electropolymerized polypyrrole films

The effect of electrolyte concentration on the electropolymerization of pyrrole was investigated by studies of conductivity, tensile strength, and absorption spectra, etc., of polypyrrole films prepared from electrolyte aqueous solutions. The electrolyte salts used in the studies include sodium p-toluenesulfonate (TsONa), NaClO₄, NaNO₃, and KCl. Cyclic voltammetry and elemental analysis were also performed in the studies of the effect of the NaNO₃ concentration. The conductivity, tensile strength, and the counteranion doping degree of conducting polypyrrole films increased obviously with increase of the electrolyte concentration of their polymerization solutions from 0.2 to 1 mol L⁻¹. Further increase of the concentration over 1 mol L⁻¹ has a weak effect on the further improvement of the film quality of polypyrrole. So, 1 mol L₋₁ was recommended for the electrolyte concentration of the polymerization aqueous solutions of pyrrole. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2739–2744, 1997     

Multiobjective optimization of microalgae (Chlorella sp.) growth in a photobioreactor using Box‐Behnken design approach

This study investigates a parameter optimization approach to maximize the specific growth rate of the Chlorella vulgaris microalgae species, its biomass productivity, and CO₂ capture rate. For this purpose, the Box‐Behnken experimental design technique is applied with temperature, nitrogen to phosphorus ratio, and light‐dark cycle per day, as the growth controlling parameters. For each response, a quadratic model is developed separately describing the algal specific growth rate, biomass productivity, and CO₂ capture rate, respectively. The maximum specific growth rate of 0.84 d^?1 is obtained at 25 °C, with a nitrogen to phosphorus ratio of 3.4:1, and light‐dark cycles of 24/0 h. Maximum biomass productivity of 147.3 mg L^?1 d^?1 is found at 30 °C, with a nitrogen to phosphorus ratio of 3:1, and light‐dark cycles of 12/12 h. In addition, the maximum CO₂ capture rate of 159.5 mg L^?1 d^?1 is also obtained at 30 °C, with a nitrogen to phosphorus ratio of 4:1, and light‐dark cycles of 23/1 h. Finally, a multi‐response optimization method is applied to maximize the specific growth rate, biomass productivity, and CO₂ capture rate, simultaneously. The optimal set of 30 °C, a nitrogen to phosphorus ratio 3:1, and light‐dark cycles 16/8 h, provide the maximum specific growth rate of 0.66 per day, biomass productivity of 147.6 mg L^?1 d^?1, and CO₂ capture rate of 141.7 mg L^?1 d^?1.

     

Utilization of response surface methodology to optimize the culture media for the production of rhamnolipids by Pseudomonas aeruginosa AT10

Pseudomonas aeruginosa AT10 produced a mixture of surface‐active rhamnolipids when cultivated on mineral medium with waste free fatty acids as carbon source. The development of the production process to an industrial scale included the design of the culture medium. A 2⁴ full factorial, central composite rotational design and response surface modelling method (RSM) was used to enhance rhamnolipid production by Pseudomonas aeruginosa AT10. The components that are critical for the process medium were the carbon source, the nitrogen source (NaNO₃), the phosphate content (K₂ HPO₄/KH₂PO₄ 2:1) and the iron content (FeSO₄·7H₂O). Two responses were measured, biomass and rhamnolipid production. The maximum biomass obtained was 12.06 g dm^?3 DCW, when the medium contained 50 g dm^?3 carbon source, 9 g dm^?3 NaNO₃, 7 g dm^?3 phosphate and 13.7 mg dm^?3 FeSO₄·7H₂O. The maximum concentration of rhamnolipid, 18.7 g dm^?3, was attained in medium that contained 50 g dm^?3 carbon source, 4.6 g dm^?3 NaNO₃, 1 g dm^?3 phosphate and 7.4 mg dm^?3 FeSO₄·7H₂O. © 2002 Society of Chemical Industry     

Medium optimization for lipid production through co‐fermentation of glucose and xylose by the oleaginous yeast Lipomyces starkeyi

Co‐fermentation of lignocellulose‐based carbohydrates is a potential solution to improve the economics of microbial lipid production. In the present paper, experiments were performed to optimize the media composition for lipid production by the oleaginous yeast Lipomyces starkeyi AS 2.1560 through co‐fermentation of glucose and xylose (2 : 1 wt/wt). Statistical screening of nine media variables was performed by a Plackett–Burman design. Three factors, namely mixed sugar, yeast extract and FeSO₄, were found as significant components influencing cellular lipid accumulation. Further optimization was carried out using a Box–Behnken factorial design to study the effects of these three variables on lipid production. A mathematical model with the R² value at 96.66% was developed to show the effect of each medium composition and their interactions on the lipid production. The model estimated that a maximal lipid content of 61.0 wt‐% could be obtained when the concentrations of mixed sugar, yeast extract and FeSO₄ were at 73.3 g/L (glucose 48.9 g/L, xylose 24.4 g/L), 7.9 g/L and 4.0 mg/L, respectively. The predicted value was in good accordance with the experimental data of 61.5%. Compared with the initial media, the optimized media gave 1.59‐fold and 2.03‐fold increases for lipid content and lipid productivity, respectively.     

Production of 11R-hydroxyeicosatetraenoic acid from arachidonic acid by Escherichia coli cells expressing arachidonate 11R-lipoxygenase from Nostoc sp.

Linoleate 9R-lipoxygenase (9R-LOX) from Nostoc sp. SAG 25.82 was identified as arachidonate (ARA) 11R-LOX by the determination of the product obtained from the conversion of ARA. The specific activity and catalytic efficiency (k_cat/K_m) of the enzyme for C20 and C22 polyunsaturated fatty acids followed the order ARA > eicosapentaenoic acid > docosahexaenoic acid. The production of the lipid mediator 11R-hydroxyeicosatetraenoic acid (11R-HETE) was performed using Escherichia coli cells expressing ARA 11R-LOX from Nostoc sp. The reaction conditions, such as pH, temperature, solvent and its concentration, and substrate and cell concentrations, were optimized using the recombinant cells, and the optimal conditions for the production of 11R-HETE from ARA were pH 7.0, 25°C, 10 g L⁻¹ cells, 5.0 mM ARA, 4% (v/v) ethanol, and 10 mM cysteine as a reducing agent. Under these optimized conditions, E. coli cells expressing 11R-LOX converted 5.0 mM ARA into 4.74 mM 11R-HETE in 60 min, with a molar conversion yield of 95% a volumetric productivity of 79 μM min⁻¹ and a specific productivity of 7.9 μM min⁻¹ g⁻¹. To the best of our knowledge, this is the first report on the quantitative biotechnological production of 11R-HETE.     

Influence of Temperature on Growth and Peak Oil Biosynthesis in a Carbon-Limited Medium by <Emphasis Type="Italic">Pythium irregulare</Emphasis>

Kinetic analysis was investigated for a carbon-limited medium (C/N ratio = 5.0) supporting the growth of the 5,8,11,14,17-eicosapentaenoic acid (20:5; ω-3) (EPA)-accumulating fungal organism Pythium irregulare. The productivity and yield parameters at three temperatures, 14, 21, and 28°C, demonstrated growth-coupled synthesis for lipid-free biomass growth and lipid accumulation. For this system, the maximum specific growth rate and theoretical maximum biomass yield based on logistic growth kinetics were used to determine an activation energy of the growth process, E _g, of 36.5 kJ mol⁻¹. At 14, 21, and 28°C, peak lipid yield occurred after culturing for 7, 4, and 3 days, respectively, with peak lipid yields of 8.14, 12.8, and 6.69 g lipid 100 g⁻¹ glucose. At these peak yields, the maximum lipid-free biomass productivity was achieved at the colder 14°C temperature as well as an increased concentration of EPA—10.9 wt%. Despite these enhancements, the maximum relative lipid production (P _R(FA/B)) was achieved at 21°C—19.1%.     

Application of the Stover–Kincannon kinetic model to nitrogen removal by Chlorella vulgaris in a continuously operated immobilized photobioreactor system

BACKGROUND: The aim of this study was to evaluate the ammonium nitrogen removal performance of algae culture Chlorella vulgaris in a novel immobilized photobioreactor system under different operating conditions and to determine the biokinetic coefficients using the Stover–Kincannon model. RESULTS: The photobioreactor was continuously operated at different initial ammonium nitrogen concentrations (NH₄‐N₀ = 10–48 mg L⁻¹), hydraulic retention times (HRT = 1.7–5.5 days) and nitrogen/phosphorus ratios (N/P = 4/1–13/1). Effluent NH₄‐N concentrations varied between 2.1 ± 0.5 mg L⁻¹ and 26 ± 1.2 mg L⁻¹ with increasing initial NH₄‐N concentrations from 10 ± 0.6 mg L⁻¹ to 48 ± 1.8 mg L⁻¹ at θ_H = 2.7 days. The maximum removal efficiency was obtained as 79 ± 4.5% at 10 mg L⁻¹ NH₄‐N concentration. Operating the system for longer HRT improved the effluent quality, and the percentage removal increased from 35 ± 2.4% to 93 ± 0.2% for 20 mg L⁻¹ initial NH₄‐N concentration. The N/P ratio had a substantial effect on removal and the optimum ratio was determined as N/P = 8/1. Saturation value constant, and maximum substrate utilization rate constant of the Stover–Kincannon model for ammonium nitrogen removal by C. vulgaris were determined as K_B = 10.3 mg L⁻¹ d⁻¹, U_max = 13.0 mg L⁻¹ day⁻¹, respectively. CONCLUSION: Results indicated that the algae‐immobilized photobioreactor system had an effective nitrogen removal capacity when the operating conditions were optimized. The optimal conditions for the immobilized photobioreactor system used in this study can be summarized as HRT = 5.5 days, N/P = 8 and NH₄‐N₀ = 20 mg L⁻¹ initial nitrogen concentration to obtain removal efficiency greater than 90%. Copyright © 2008 Society of Chemical Industry     

Production of Medium-Chain-Length Poly(3-hydroxyalkanoates) from Crude Fatty Acids Mixture by Pseudomonas putida

Microbial production of medium-chain-length poly(3-hydroxyalkanoates), PHA_MCL from crude fatty acids mixture was investigated. With ammonium as the growth limiting substrate, fatty acids mixture from saponified palm kernel oil (SPKO) supports good growth and PHA_MCL production of Pseudomonas putida PGA1. Growth of this microorganism on ammonium exhibited substrate inhibition kinetics which can be described using Andrews model with the substrate inhibition constant, K_i = 1.2 g L⁻¹. Concentration of SPKO in the aqueous medium should be at 10 g L⁻¹ or less, as higher concentrations can significantly reduced the volumetric oxygen transfer coefficient (K_La), biomass growth and PHA_MCL production. Uptake of SPKO by the organism follows a zero-order kinetics, indicating a mass transfer limitation of the free fatty acids by the P. putida PGA1 cells. In batch and fed-batch fermentations, PHA_MCL accumulation is encouraged under ammonium-limited condition with SPKO as the sole carbon and energy source. The amount of PHA_MCL accumulated and its specific production rate, q_PHA were influenced by the residual ammonium concentration level in the culture medium. It was observed that in both fermentation modes, when the residual ammonium becomes exhausted (<0.05 g L⁻¹), the PHA_MCL accumulation and q_PHA were significantly reduced. However, this effect can be reversed by feeding low amount of ammonium to the culture, resulting in significantly improved PHA_MCL yield and productivity. It is concluded that the feeding of residual ammonium concentration in the culture medium during the PHA_MCL accumulation has a positive effect on sustaining the PHA_MCL biosynthetic capability of the organism.     

Effect of nitrogen sources on γ-linolenic acid accumulation in Spirulina platensis

The effect of ammonium phosphate on the growth, lipid content, and γ-linolenic acid accumulation was determined in the cyanobacterium Spirulina platensis. After 14 d on media containing 0.041 g N/L, γ-linolenic acid concentration of cultured cells increased up to 35.3±0.13%, w/w. In treatments containing NaNO₃, NH₄NO₃, and NH₄Cl, γ-linolenic acid concentration increased up to 31.2±0.23%, w/w. After the same period, lipid content in the dry biomass was 12.2±0.03%, w/w, with (NH₄)₂HPO₄ compared to about 14.1±0.12%, w/w, in treatments with NaNO₃. When (NH₄)₂HPO₄ concentration in the medium was increased to 0.082 g N/L, 30.8±0.28%, w/w, γ-linolenic acid had formed after 10 d and the lipid percentage in the dry cell mass was 16.7±0.16%, w/w. However, in treatments with NaNO₃, NH₄NO₃, or NH₄Cl, γ-linolenic acid concentration increased up to 30.6±0.23%, w/w, and the lipid content was found to be 18.0±0.17 to 18.9±0.03%, w/w. These data showed that (NH₄)₂HPO₄ is a suitable source of nitrogen for growth of S. platensis, with increased accumulation of γ-linolenic acid at lower N concentration.     

Influence of Aerobic Pretreatment with Penicillium decumbens on the Anaerobic Digestion of Beet Molasses Alcoholic Fermentation Wastewater in Suspended and Immobilized Cell Bioreactors

A comparative study was carried out on the anaerobic digestion of untreated and previously-fermented (with Penicillium decumbens) beet molasses. Four continuous stirred tank reactors were used for the study, two with freely suspended biomass, and the other with biomass supported on saponite. The reactors operated satisfactorily between hydraulic retention times (HRT) of 53·3–10·6 days and 15·4–3·1 days for untreated and previously-fermented molasses respectively. The anaerobic digestion processes of untreated and pretreated molasses were found to follow first-order kinetics for biomass loading rates in the range of 0–0·55 and 0–0·75 g chemical oxygen demand (COD) g⁻¹ volatile suspended solids (VSS) day⁻¹ respectively. The experimental data [namely unitary conversion or efficiency (X), HRT, biomass concentration (M) and incoming substrate concentration (S₀)] conformed to an equation of the form: X/HRT = KM(1-X)–(KMS_R/S₀), from which the kinetic constant, K, was calculated. The kinetic constants were influenced by the pretreatment carried out and were 1·7 and 2·5 times higher for pretreated molasses than for untreated molasses in the reactors with suspended and immobilized biomass respectively. This was significant at a 95% confidence level. The specific rate of substrate uptake for cell maintenance (m) decreased by a factor of approximately 2 for the previously fermented molasses in relation to the observed values for the untreated molasses. This may be attributable to the fact that higher phenolic compound concentrations inhibit and interfere with the activity of anaerobic bacteria. © 1997 SCI.     

Biosurfactant Production by Bacillus tequilensis ZSB10: Structural Characterization,Physicochemical, and Antifungal Properties

A new biosurfactant was obtained from a moderately halophilic bacterium identified as Bacillus tequilensis ZSB10 that was isolated from a saline water pond located in Tehuacan-Cuicatlan valley, Mexico. A kinetic analysis of the bacterial growth of the ZSB10 strain showed a maximum growth at 24 h regardless of the initial pH (5, 7.4, and 9). The best results were found at pH = 7.4 in terms of bacterial growth, besides which the produced biosurfactant showed emulsifying and surfactant properties with an emulsification index (E₂₄) and surface tension change (ΔST) of 54 ± 0% and 26 mN m⁻¹, respectively. Extracted ZSB10 crude biosurfactant had a yield of 106 ± 6 mg L⁻¹, an E₂₄ = 58.4 ± 0.2%, and a ΔST = 26 mN m⁻¹ with a critical micelle concentration (CMC) of 44.82 mg L⁻¹. Also, its structure was characterized by MALDI-TOF mass spectrometry as a surfactin, iturin A, and fengycin mixture whose main isoform was leu/ile-7 C₁₅ surfactin [M + Na]⁺. Finally, the ZSB10 crude biosurfactant showed antifungal activity against Helminthosporium sp., with a 79.3% growth inhibition and an IC₅₀ of 1.37 mg per disc. Therefore, this biosurfactant could be used as biopesticide.     

Optimization of chitosanase production from Bacillus sp. RKY3 using statistical experimental designs

BACKGROUND: The culture medium and fermentation conditions for the production of constitutive chitosanase from a newly isolated Bacillus sp. RKY3 were optimized statistically. RESULTS: The variables significantly influencing both chitosanase production and cell growth were screened through the Plackett–Burman design, by which maltose, beef extract, MgSO₄, and incubation time were identified as the most significant variables. The optimum values of the selected variables and their mutual interactions were determined through the steepest ascent method and Box–Behnken experimental design. The results demonstrated that 62.30 U mL^?1 chitosanase activity was predicted with optimum conditions of maltose (30.18 g L^?1), beef extract (15.25 g L^?1), MgSO₄ (0.26 g L^?1), and incubation time (50.02 h). The predicted response was verified by the validation experiments, and the optimum conditions resulted in a maximum chitosanase activity of 63.53 ± 1.22 U mL^?1. CONCLUSION: The optimization of fermentation variables resulted in an approximately 11.3‐fold increase in chitosanase activity compared with that observed under unoptimized conditions (from 5.63 U mL^?1 to 63.53 U mL^?1). Copyright © 2009 Society of Chemical Industry