Effects of pH profiles on nisin production in biofilm reactor

Apart from its widely accepted commercial applications as a food preservative, nisin emerges as a promising alternative in medical applications for bacterial infection in both humans and livestock. Improving nisin production through optimization of fermentation parameters would make nisin more cost-effective for various applications. Since nisin production by Lactococcus lactis NIZO 22186 was highly influenced by the pH profile employed during fermentation, three different pH profiles were evaluated in this study: (1) a constant pH profile at 6.8 (profile 1), (2) a constant pH profile with autoacidification at 4 h (profile 2), and (3) a stepwise pH profile with pH adjustment every 2 h (profile 3). The results demonstrated that the low-pH stress exerted during the first 4 h of fermentation in profile 3 detrimentally affected nisin production, resulting in a very low maximum nisin concentration (593 IU ml⁻¹). On the other hand, growth and lactic acid production were only slightly delayed, indicating that the loss in nisin production was not a result of lower growth or shifting of metabolic activity toward lactic acid production. Profile 2, in which pH was allowed to drop freely via autoacidification after 4 h of fermentation, was found to yield almost 1.9 times higher nisin (3,553 IU ml⁻¹) than profile 1 (1,898 IU ml⁻¹), possibly as a result of less adsorption of nisin onto producer cells. Therefore, a combination of constant pH and autoacidification period (profile 2) was recommended as the pH profile during nisin production in a biofilm reactor.     

Effects of pH profiles on nisin fermentation coupling with foam separation

Online foam separation was proposed to recover nisin during fermentation of Lactococcus lactis subsp. lactis ATCC 11454. Firstly, the optimal pH profile of nisin fermentation was investigated including different realkalization set values and pH drop gradients. Then the selected pH profiles of 5.75 ± 0.05 and 6.25–5.75 (±0.02) were used to perform nisin fermentation coupling with foam separation. The results showed that pH profile of 5.75 ± 0.05 was better than that of 6.25–5.75 (±0.02) for online foam separation. With the optimal pH profile, an aeration of 20 ml min⁻¹ that started at 8 h of incubation and lasted for 2 h resulted in 6.6 times higher specific productivity than that of the fermentation without aeration. Nisin synthesis was therefore prolonged with low sucrose concentration in the culture broth, which indicated that the feedback inhibition of nisin is more influential than the substrate limitation of sucrose in the late phase of nisin fermentation. Total nisin production (4,870 ± 180 IU ml⁻¹) was increased by 30.3% with online foam separation. This effective online recovery method for nisin production could be easily scaled up due to the facile operation of foaming process.     

Evaluation of culture medium for nisin production in a repeated-batch biofilm reactor

In this study, a biofilm reactor with plastic composite support (PCS), made by high-temperature extrusion of agricultural products and polypropylene, was evaluated for nisin production using L. lactis strain NIZO 22186. The high-biomass density of the biofilm reactor was found to contribute to a significantly shorter lag time of nisin production relative to a suspended-cell reactor. In comparison to glucose (579 IU/mL), sucrose significantly increased the nisin production rate by 1.4-fold (1100 IU/mL). However, results revealed that high levels of sucrose (8% w/v) had a suppressing effect on nisin production and a stimulating effect on lactic acid production. A high concentration of MgSO4.7H2O at 0.04% (w/v) was found to reduce the nisin production, while concentrations of KH2PO4 of up to 3% (w/v) did not have any significant effect on growth or nisin production. The best of the tested complex media for nisin production using the PCS biofilm reactor consisted of 4% (w/v) sucrose, 0.02% (w/v) MgSO4.7H2O, and 0.1% (w/v) KH2PO4. Nisin production rate in the biofilm reactor was significantly increased by 3.8-fold (2208 IU/mL) when using the best complex medium tested.     

Improvement of nisin production in pH feed-back controlled,fed-batch culture by <Emphasis Type="Italic">Lactococcus lactis</Emphasis>subsp<Emphasis Type="Italic">. lactis</Emphasis>

Nisin production by Lactococcus lactis subsp. lactisin fed-batch culture was doubled by using a pH feed-back controlled method. Sucrose concentration was controlled at 10 g l^–1 giving 5010 IU nisin ml^–1 compared to 2660 IU nisin ml^–1 in batch culture.     

Evaluation of plastic-composite supports in repeated fed-batch biofilm lactic acid fermentation by Lactobacillus casei

A customized stirred-tank biofilm reactor was designed for plastic-composite supports (PCS). In repeated-batch studies, the PCS-biofilm reactors outperformed the suspended-cell reactors by demonstrating higher lactic acid productivities (2.45 g l(-1) h(-1) vs 1.75 g l(-1) h(-1)) and greater glucose consumption rates (3.27 g l(-1) h(-1) vs 2.09 g l(-1) h(-1)). In the repeated fed-batch studies, reactors were spiked periodically with concentrated glucose (75%) to maintain a concentration of approximately 80 g of glucose l(-1) in the bioreactor. In suspended-cell fermentations with 10 g of yeast extract (YE) l(-1) and zero, one, two, and three glucose spikes, the lactic acid productivities were 2.64, 1.58, 0.80, and 0.62 g l(-1) h(-1), respectively. In comparison, biofilm reactors with 7 g of YE l(-1) and zero, one, two, and three glucose spikes achieved lactic acid productivities of 4.20, 2.78, 0.66, and 0.94 g l(-1) h(-1), respectively. The use of nystatin (30 U ml(-1)) subdued the contaminating yeast population with no effect on the lactic acid productivity of the biofilm reactors, but it did affect productivity in the suspended-cell bioreactor. Overall, in repeated fed-batch fermentations, the biofilm reactors consistently outperformed the suspended-cell bioreactors, required less YE, and produced up to 146 g of lactic acid l(-1) with 7 g of YE l(-1), whereas the suspended-cell reactor produced 132 g l(-1) with 10 g of YE l(-1).     

Implementation of fed-batch strategies for vitamin K (menaquinone-7) production by Bacillus subtilis natto in biofilm reactors

Recent studies show the essential health benefits associated with vitamin K, especially menaquinone-7 (MK-7). These benefits include reducing risks of cardiovascular diseases, osteoporosis, and even cancer. However, MK-7 production on an industrial level is only possible through bacterial fermentation and also current static fermentation strategies are not potent enough with difficulties to scale up. Biofilm reactors, however, may be a practical alternative. Biofilm reactors provide a controlled environment for the microorganisms to form mature and robust biofilms that enable them to produce value-added products with enhanced efficiencies. In this study, fed-batch addition of glucose and glycerol were investigated to the base media in biofilm reactors, as carbon source addition seemed crucial in batch fermentations. Results indicated that fed-batch strategies can be significantly effective in glucose-based medium, increasing the end-product concentrations to 28.7 ± 0.3 mg/L of MK-7 which was 2.3 fold higher than the level produced in suspended-cell bioreactors and renders the biofilm reactors as a potential replacement for static fermentation strategies. Moreover, morphological changes of B. subtilis were tracked during the 12-day long fermentation runs and finally, SEM investigations confirmed significant biofilm and extracellular matrices formed on the plastic composite support (PCS) in the biofilm reactors. In conclusion, biofilm reactors especially with fed-batch fermentation regimes seem to be an effective tool for MK-7 production at industrial scales.

     

Recent advances in ABE fermentation: hyper-butanol producing Clostridium beijerinckii BA101

This is an overview of the mutant strain Clostridium beijerinckii BA101 which produces solvents (acetone–butanol–ethanol, ABE) at elevated levels. This organism expresses high levels of amylases when grown on starch. C. beijerinckii BA101 hydrolyzes starch effectively and produces solvent in the concentration range of 27–29 g l⁻¹. C. beijerinckii BA101 has been characterized for both substrate and butanol inhibition. Supplementing the fermentation medium (MP2) with sodium acetate enhances solvent production to 33 g l⁻¹. The results of studies utilizing commercial fermentation medium and pilot plant-scale reactors are consistent with the results using small-scale reactors. Pervaporation, a technique to recover solvents, has been applied to fed-batch reactors containing C. beijerinckii BA101, and solvent production as high as 165 g l⁻¹ has been achieved. Immobilization of C. beijerinckii BA101 by adsorption and use in a continuous reactor resulted in reactor productivity of 15.8 g l⁻¹ h⁻¹. Recent economic studies employing C. beijerinckii BA101 suggested that butanol can be produced at US$0.20–0.25 lb⁻¹ by employing batch fermentation and distillative recovery. Application of new technologies such as pervaporation, fed-batch culture, and immobilized cell reactors is expected to further reduce these prices. Journal of Industrial Microbiology & Biotechnology (2001) 27, 287–291. Received 12 September 2000/ Accepted in revised form 27 January 2001     

Induction of xylanases by sugar cane bagasse at different cell densities of Cellulomonas flavigena

The effect of cell density on xylanolytic activity and productivity of Cellulomonas flavigena was evaluated under two different culturing conditions: fed-batch culture with discontinuous feed of sugar cane bagasse (SCB; condition 1) and glycerol fed-batch culture followed by addition of SBC as xylanases inducer (condition 2). The enzymatic profile of xylanases was similar in both systems, regardless of the initial cell density at time of induction. However, the xylanolytic activity changed with initial cell density at the time of induction (condition 2). The maximum volumetric xylanase activity increased with increased initial cell density from 4 to 34 g l⁻¹ but decreased above this value. The largest total volumetric xylanase productivity under condition 2 (1.3 IU ml⁻¹ h⁻¹) was significantly greater compared to condition 1 (maximum 0.6 IU ml⁻¹ h⁻¹). Consequently, induction of xylanase activity by SCB after growing of C. flavigena on glycerol at intermediate cell density can be a feasible alternative to improve activity and productivity of xylanolytic enzymes.     

Production and characterization of thermostable xylanase and pectinase from Streptomyces sp. QG-11-3

Streptomyces sp. QG-11-3, which produces a cellulase-free thermostable xylanase (96 IU ml⁻¹) and a pectinase (46 IU ml⁻¹), was isolated on Horikoshi medium supplemented with 1% w/v wheat bran. Carbon sources that favored xylanase production were rice bran (82 IU ml⁻¹) and birch-wood xylan (81 IU ml⁻¹); pectinase production was also stimulated by pectin and cotton seed cake (34 IU ml⁻¹ each). The partially purified xylanase and pectinase were optimally active at 60°C. Both enzymes were 100% stable at 50°C for more than 24 h. The half-lives of xylanase and pectinase at 70, 75 and 80°C were 90, 75 and 9 min, and 90, 53 and 7 min, respectively. The optimum pH values for xylanase and pectinase were 8.6 and 3.0, respectively, at 60°C. Xylanase and pectinase were stable over a broad pH range between 5.4 and 9.4 and 2.0 to 9.0, respectively, retaining more than 85% of their activity. Ca²⁺ stimulated the activity of both enzymes up to 7%, whereas Cd²⁺, Co²⁺, Cr³⁺, iodoacetic acid and iodoacetamide inhibited xylanase up to 35% and pectinase up to 63%; at 1 mM, Hg²⁺ inhibited both enzymes completely. Journal of Industrial Microbiology & Biotechnology (2000) 24, 396–402. Received 29 September 1999/ Accepted in revised form 02 February 2000     

Modelling the production of nisin by Lactococcus lactis in fed-batch culture

Nisin production in batch culture and fed-batch cultures (sucrose feeding rates were 6, 7, 8, and 10 g l^–1 h^–1, respectively) by Lactococcus lactis subsp. lactis ATCC 11454 was investigated. Nisin production showed primary metabolite kinetics, and could be improved apparently by altering the feeding strategy. The nisin titer reached its maximum, 4,185 IU ml^–1, by constant addition of sucrose at a feeding rate of 7 g l^–1 h^–1; an increase in 58% over that of the batch culture (2,658 IU ml^–1). Nisin biosynthesis was affected strongly by the residual sucrose concentration during the feeding. Finally, a mathematical model was developed to simulate the cell growth, sucrose consumption, lactic acid production and nisin production. The model was able to describe the fermentation process in all cases.     

Production of cyclodextrin glucanotransferase from an alkalophilic <Emphasis Type="Italic">Bacillus</Emphasis> sp. by pH-stat fed-batch fermentation

Batch and fed-batch fermentation processes were employed to culture an alkalophilic Bacillus sp. for the production of cyclodextrin glucanotransferase (CGTase). CGTase production was repressed by glucose and induced by soluble starch. By fed-batch fermentation, a CGTase activity up to 56 unit ml⁻¹ with 65 g dry cells l⁻¹ were achieved. The CGTase activity and cell density were increased 360 and 510%, respectively, from those values achieved with batch fermentation.     

Inhibition by nisin of K+ uptake in a sensitivePediococcus sp. strain

Summary A nisin-sensitive strain ofPediococcus sp possessed an uptake system for K⁺ which was apparently dependent on metabolic energy and ATPase activity. K⁺ uptake rate was dependent on the glucose and K⁺ concentrations and showed approximately Michaelis-Menten kinetics with respect to both of these variables with K_t values of 1.2 mM and 599 μM respectively. The presence of nisin inhibited K⁺ uptake with the percentage inhibition proportional to the nisin activity,. Total inhibition occurred at between 4.5 and 5.0 IU ml⁻¹ and the MIC was approximately 0.6 IU ml⁻¹.     

Continuous production of poly([<Emphasis Type="BoldItalic">R</Emphasis>]-3-hydroxybutyrate) by <Emphasis Type="BoldItalic">Cupriavidus necator</Emphasis> in a multistage bioreactor cascade

Poly(hydroxyalkanoates) (PHAs) constitute biodegradable polyesters and are considered among the most promising candidates to replace common petrochemical plastics in various applications. To date, all commercial processes for PHA production employ microbial discontinuous fed-batch fermentations. These processes feature drawbacks such as varying product quality and the inevitable periods of downtime for preparation and post-treatment of the bioreactor equipment. An unprecedented approach to PHA production was chosen in the presented work using a multistage system consisting of five continuous stirred tank reactors in series (5-SCR), which can be considered as a process engineering substitute of a continuous tubular plug flow reactor. The first stage of the reactor cascade is the site of balanced bacterial growth; thereafter, the fermentation broth is continuously fed from the first into the subsequent reactors, where PHA accumulation takes place under nitrogen-limiting conditions. Cupriavidus necator was used as production strain. The focus of the experimental work was devoted to the development of a PHA production process characterized by high productivity and high intracellular polymer content. The results of the experimental work with the reactor cascade demonstrated its potential in terms of volumetric and specific productivity (1.85 g L⁻¹ h⁻¹ and 0.100 g g⁻¹ h⁻¹, respectively), polymer content (77%, w/w) and polymer properties (M _w = 665 kg/mol, PDI = 2.6). Thus, implementing the technology for 5-SCR production of PHB results in an economically viable process. The study compares the outcome of the work with literature data from continuous two-stage PHA production and industrial PHA production in fed-batch mode.     

Online recovery of nisin during fermentation and its effect on nisin production in biofilm reactor

An online removal of nisin by silicic acid coupled with a micro-filter module was proposed as an alternative to reduce detrimental effects caused by adsorption of nisin onto producer, enzymatic degradation by protease, and product inhibition during fermentation. In this study, silicic acid was successfully used to recover nisin from the fermentation broth of Lactococcus lactis subsp. lactis NIZO 22186. The effect of pH (at 6.8 and 3.0) during adsorption process and several eluents (deionized water, 20% ethanol, 1 M NaCl, and 1 M NaCl + 20% ethanol) for desorption were evaluated in a small batch scale. Higher nisin adsorption onto silicic acid was achieved when the adsorption was carried out at pH 6.8 (67% adsorption) than at pH 3.0 (54% adsorption). The maximum recovery was achieved (47% of nisin was harvested) when the adsorption was carried out at pH 6.8 and 1 M NaCl + 20% ethanol was used as an eluent for desorption. Most importantly, nisin production was significantly enhanced (7,445 IU/ml) when compared with the batch fermentation without the online recovery (1,897 IU/ml). This may possibly be attributed to preventing the loss of nisin due the detrimental effects and a higher biomass density achieved during online recovery process, which stimulated production of nisin during fermentation.     

The role of nisin in fuel ethanol production with Saccharomyces cerevisiae

Aims: To investigate the effects of nisin on lactobacilli contamination of yeast during ethanol fermentation and to determine the appropriate concentration required to control the growth of selected lactobacilli in a YP/glucose media fermentation model. Methods and Results: The lowest concentration of nisin tested (5 IU ml^?1) effectively controlled the contamination of YP/glucose media with 10⁶ CFU ml^?1 lactobacilli. Lactic acid yield decreased from 5·0 to 2·0 g l^?1 and potential ethanol yield losses owing to the growth and metabolism of Lactobacillus plantarum and Lactobacillus brevis were reduced by 11 and 7·8%, respectively. Approximately, equal concentrations of lactic acid were produced by Lact. plantarum and Lact. brevis in the presence of 5 and 2 IU ml^?1 nisin, respectively, thus demonstrating the relatively higher nisin sensitivity of Lact. brevis for the strains in this study. No differences were observed in the final ethanol concentrations produced by yeast in the absence of bacteria at any of the nisin concentrations tested. Conclusions: Metabolism of contaminating bacteria was reduced in the presence of 5 IU ml^?1 nisin, resulting in reduced lactic acid production and increased ethanol production by the yeast. Significance and Impact of the Study: Bacteriocins represent an alternative to the use of antibiotics for the control of bacterial contamination in fuel ethanol plants and may be important in preventing the emergence of antibiotic‐resistant contaminating strains.     

Production of nisin with continuous adsorption to Amberlite XAD-4 resin using<Emphasis Type="Italic"> Lactococcus lactis</Emphasis> N8 and<Emphasis Type="Italic"> L. lactis</Emphasis> LAC48

The production of nisin, biomass and lactic acid in pH-controlled and uncontrolled batch fermentation and batch fermentation (pH 5.5) with continuous removal of nisin was examined in the parent strain Lactococcus lactis N8 and LAC48. Strain LAC48 in batch fermentor (pH not controlled) gave a maximum nisin concentration of 2.5×10⁶ IU g dcw^–1. The nisin concentration remained high (2.0×10⁶ IU g dcw^–1) after the logarithmic growth phase (10–22 h), whereas nisin production of strain N8 decreased after the logarithmic growth phase. The maximum nisin production of strain LAC48 was not directly related to the biomass formation and not associated with growth. In order to study end product inhibition in nisin production, a system was built for adsorption of nisin during fermentation. The adsorbent Amberlite XAD-4 was found to have an effective binding capacity for nisin. Cells of LAC48 and N8 compensated for the removal of nisin, indicating that nisin production also occurs in the stationary phase.     

Ethanol production from sweet sorghum juice in batch and fed-batch fermentations by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Sweet sorghum juice supplemented with 0.5% ammonium sulphate was used as a substrate for ethanol production by Saccharomyces cerevisiae TISTR 5048. In batch fermentation, kinetic parameters for ethanol production depended on initial cell and sugar concentrations. The optimum initial cell and sugar concentrations in the batch fermentation were 1 × 10⁸ cells ml⁻¹ and 24 °Bx respectively. At these conditions, ethanol concentration produced (P), yield (Y _ps) and productivity (Q _p ) were 100 g l⁻¹, 0.42 g g⁻¹ and 1.67 g l⁻¹ h⁻¹ respectively. In fed-batch fermentation, the optimum substrate feeding strategy for ethanol production at the initial sugar concentration of 24 °Bx was one-time substrate feeding, where P, Y _ps and Q _p were 120 g l⁻¹, 0.48 g g⁻¹ and 1.11 g l⁻¹ h⁻¹ respectively. These findings suggest that fed-batch fermentation improves the efficiency of ethanol production in terms of ethanol concentration and product yield.     

Production,purification and characterization of <Emphasis Type="Italic">Bacillus</Emphasis> sp. GRE7 xylanase and its application in eucalyptus Kraft pulp biobleaching

Production of extracellular xylanase from Bacillus sp. GRE7 using a bench-top bioreactor and solid-state fermentation (SSF) was attempted. SSF using wheat bran as substrate and submerged cultivation using oat-spelt xylan as substrate resulted in an enzyme productivity of 3,950 IU g⁻¹ bran and 180 IU ml⁻¹, respectively. The purified enzyme had an apparent molecular weight of 42 kDa and showed optimum activity at 70°C and pH 7. The enzyme was stable at 60–80°C at pH 7 and pH 5–11 at 37°C. Metal ions Mn²⁺ and Co²⁺ increased activity by twofold, while Cu²⁺ and Fe²⁺ reduced activity by fivefold as compared to the control. At 60°C and pH 6, the K _m for oat-spelt xylan was 2.23 mg ml⁻¹ and V _max was 296.8 IU mg⁻¹ protein. In the enzymatic prebleaching of eucalyptus Kraft pulp, the release of chromophores, formation of reducing sugars and brightness was higher while the Kappa number was lower than the control with increased enzyme dosage at 30% reduction of the original chlorine dioxide usage. The thermostability, alkali-tolerance, negligible presence of cellulolytic activity, ability to improve brightness and capacity to reduce chlorine dioxide usage demonstrates the high potential of the enzyme for application in the biobleaching of Kraft pulp.     

Nisin production in a chitin-including continuous fermentation system with Lactococcus lactis displaying a cell wall chitin-binding domain

The limiting factors in the continuous production of nisin are high amount of biomass loss and low dilution rate application. In this study, a chitin-including continuous nisin fermentation system (CICON-FER) was constructed for high volumetric nisin production using nisin producer L. lactis displaying cell wall chitin-binding domain (ChBD) together with chitin in the reactor. In this respect, the highest binding conditions of relevant L. lactis cells to chitin were determined. Then the chitin flakes carrying nisin-producing L. lactis cells were used within the CICON-FER system at different dilution rates (0.1–0.9 h^?1) and initial glucose concentrations (20–60 g l^?1). The results revealed that the pH 7 conditions and the use of 100 mM sodium phosphate buffer with 0.1 % Tween 20 and Triton X-100 significantly increased the binding capacity of ChBD displaying L. lactis cells to chitin. The constructed CICON-FER system maintained the presence of the ChBD surface displaying L. lactis cells in the reactor system until 0.9 h^?1 dilution rate that resulted in a considerably high level of volumetric nisin production and productivity (10,500 IU ml^?1 and 9,450 IU ml^?1 h^?1, respectively) with the combination of a 0.9-h^?1 dilution rate and a 40-g l^?1 initial glucose concentration. In conclusion, an innovative nisin fermentation system that yielded the highest nisin production thus far and that was feasible for industrial application was created.     

Extracellular production of a glycolipid biosurfactant, mannosylerythritol lipid, by Candida sp. SY16 using fed-batch fermentation

Candida sp. strain SY16 produces a glycolipid-type biosurfactant, mannosylerythritol lipid (MEL-SY16), which can reduce the surface tension of a culture broth from 72 to 30 dyne cm⁻¹ and highly emulsify hydrocarbons when cultured in soybean-oil-containing media. As such, laboratory-scale fermentation for MEL-SY16 production was performed using optimized conditions. In batch fermentation, MEL-SY16 was mainly produced during the stationary phase of growth, and the concentration of MEL-SY16 reached 37 g l⁻¹ after 200 h. The effect of pH control on the production of MEL-SY16 was also examined in batch fermentation. The highest production yield of MEL-SY16 was when the pH was controlled at 4.0, and the production was significantly improved compared to batch fermentation without pH control. In fed-batch fermentation, glucose and soybean oil (1:1, w/w) were used in combination as the initial carbon sources for cell growth, and soybean oil was used as the feeding carbon source during the MEL production phase. The feeding of soybean oil resulted in the disappearance of any foam and a sharp increase in the MEL production until 200 h, at which point the concentration of MEL-SY16 was 95 g l⁻¹. Among the investigated culture systems, the highest MEL-SY16 production and volumetric production rate were achieved with fed-batch fermentation.