Immobilization of cells for application in the food industry

Preparation and In Vitro Characterization of Lactococcus lactis-Loaded Alginate Particles as a Promising Delivery Tool for Periodontal Probiotic Therapy

Probiotic microorganisms are used in a variety of food supplements and medical formulations to promote human health. In periodontal therapy, probiotics are mainly used in the form of gels, tablets or rinses that often tend to leak from the periodontal pocket, resulting in a strongly reduced therapeutic effect. In this pilot in vitro study, we present biodegradable alginate-based particles as an alternative, highly efficient system for a periodontal delivery of probiotic bacteria to the inflammation site. For this purpose, Lactococcus (L.) lactis was encapsulated using a standardized pump-controlled extrusion-dripping method. Time-dependent bacterial release in artificial saliva was investigated over 9 days. The effect of freeze drying was explored to ensure long-term storage of L. lactis-loaded particles. Additionally, the particles were bound to dentin surface using approved bioadhesives and subjected to shear stress in a hydrodynamic flow chamber that mimics the oral cavity in vitro. Thus, round particles within the range of 0.80-1.75 mm in radius could be produced, whereby the diameter of the dripping tip had the most significant impact on the size. Although both small and large particles demonstrated a similar release trend of L. lactis, the release rate was significantly higher in the former. Following lyophilization, particles could restore their original shape within 4 h in artificial saliva; thereby, the bacterial viability was not affected. The attachment strength to dentin intensified by an adhesive could resist forces between 10 and 25 N/m2. Full degradation of the particles was observed after 20 days in artificial saliva. Therefore, alginate particles display a valuable probiotic carrier for periodontal applications that have several crucial advantages over existing preparations: a highly stable form, prolonged continuous release of therapeutic bacteria, precise manufacturing according to required dimensions at the application site, strong attachment to the tooth with low risk of dislocation, high biocompatibility and biodegradability.

Histamine-degrading halophilic bacteria from traditional fish sauce: Characterization of Virgibacillus campisalis TT8.5 for histamine reduction

Traditionally produced fish sauce can contain significant amounts of histamine. In some instances, the histamine concentration may be well above the limit recommended by the Codex Alimentarius Commission. The aim of this study was to discover new bacterial strains capable of growing under the stressful environmental conditions of fish sauce fermentation and metabolizing histamine. In this study, 28 bacterial strains were isolated from Vietnamese fish sauce products based on their ability to grow at high salt concentrations (23% NaCl) and tested for their ability to degrade histamine. Strain TT8.5 showed the highest histamine-degradation (45.1 ± 0.2% of initially 5 mM histamine within 7 days) and was identified as Virgibacillus campisalis TT8.5. Its histamine-degrading activity was shown to be localized intracellularly and the enzyme is a putative histamine dehydrogenase. The strain exhibited optimal growth and histamine-degrading activity at 37°C, pH 7%, and 5% NaCl in halophilic archaea (HA) histamine broth. It also showed pronounced histamine-degrading activity in HA histamine broth when cultivated at temperatures of up to 40 °C as well as in the presence of up to 23% NaCl. After treatment with immobilized cells, 17.6-26.9% of the initial histamine in various fish sauce products were reduced within 24 h of incubation, while no significant changes in other parameters of fish sauce quality were observed after this treatment. Our results indicate that V. campisalis TT8.5 is of potential interest to be applied in histamine degradation of traditional fish sauce.

Apple-derived 3D scaffold for improving gastrointestinal viability and in-situ growth of probiotics

This study develops a novel low-cost microbial delivery system by transforming common food materials such as apple tissue into a 3D scaffold. Apple tissue scaffold was constructed by decellularization of intact tissue using a minimal amount of sodium dodecyl sulfate (0.5 % w/v). Vacuum-assisted infusion of model probiotic Lactobacillus cells led to a high encapsulation yield of probiotic cells (10¹⁰ CFU/g of scaffold) in 3D scaffolds on a wet basis. The bio-polymer coated 3D scaffolds with infused cells significantly enhanced the survivability of infused probiotic cells during simulated gastric and intestinal digestions. In addition, imaging and plate counting results validate the growth of the infused cells in the 3D scaffold after 1-2 days of fermentation in MRS media, while cells without infusion in the scaffold had limited attachment with the intact apple tissue. Overall, these results highlight the potential of the apple tissue-derived 3D scaffold to deliver probiotic cells and include the biochemical compositions to support the growth of delivered microbial cells in the colon.

Calcium carbonate nano- and microparticles: synthesis methods and biological applications

Calcium carbonate micro- and nanoparticles are considered as chemically inert materials. Therefore, they are widely considered in the field of biosensing, drug delivery, and as filler material in plastic, paper, paint, sealant, and adhesive industries. The unusual properties of calcium carbonate-based nanomaterials, such as biocompatibility, high surface-to-volume ratio, robust nature, easy synthesis, and surface functionalization, and ability to exist in a variety of morphologies and polymorphs, make them an ideal candidate for both industrial and biomedical applications. Significant research efforts have been devoted for developing novel synthesis methods of calcium carbonate particles in micrometer and nanometer dimensions. This review highlights different approaches of the synthesis of calcium carbonate micro- and nanoparticles, such as precipitation, slow carbonation, emulsion, polymer-mediated method, including in-situ polymerization, mechano-chemical, microwave-assisted method, and biological methods. The applications of these versatile calcium carbonate micro- and nanoparticles in the biomedical field (such as in drug delivery, therapeutics, tissue engineering, antimicrobial activity, biosensing applications), in industries, and environmental sector has also been comprehensively covered.

Cutting-edge biotechnological advancement in islet delivery using pancreatic and cellular approaches

There are approximately 1 billion prediabetic people worldwide, and the global cost for diabetes mellitus (DM) is estimated to be $825 billion. In regard to Type 1 DM, transplanting a whole pancreas or its islets has gained the attention of researchers in the last few decades. Recent studies showed that islet transplantation (ILT) containing insulin-producing β cells is the most notable advancement cure for Type 1 DM. However, this procedure has been hindered by shortage and lack of sufficient islet donors and the need for long-term immunosuppression of any potential graft rejection. The strategy of encapsulation may avoid the rejection of stem-cell-derived allogeneic islets or xenogeneic islets. This review article describes various biotechnology features in encapsulation-of-islet-cell therapy for humans, including the use of bile acids.

Synthesis and characterization of quaternized agar in KOH/urea aqueous solution

Quaternized agar (QA) is synthesized in KOH/urea aqueous solution and shows low melting and gelling temperatures and antibacterial properties.

Impact of immobilization technology in industrial and pharmaceutical applications

The current demands of the world's biotechnological industries are enhancement in enzyme productivity and development of novel techniques for increasing their shelf life. Compared to free enzymes in solution, immobilized enzymes are more robust and more resistant to environmental changes. More importantly, the heterogeneity of the immobilized enzyme systems allows an easy recovery of both enzymes and products, multiple reuse of enzymes, continuous operation of enzymatic processes, rapid termination of reactions, and greater variety of bioreactor designs. This review summarizes immobilization definition, different immobilization methods, advantages and disadvantages of each method. In addition, it covers some food industries, protein purification, human nutrition, biodiesel production, and textile industry. In these industries, the use of enzymes has become an inevitable processing strategy when a perfect end product is desired. It also can be used in many other important industries including health care and pharmaceuticals applications. One of the best uses of enzymes in the modern life is their application in diagnose and treatment of many disease especially when used in drug delivery system or when used in nanoform.

Embedding live bacteria in porous hydrogel/ceramic nanocomposites for bioprocessing applications

In this work, we present a biocompatible one-pot processing route for ceramic/hydrogel nanocomposites in which we embed live bacteria. In our approach, we fabricate a highly stable alginate hydrogel with minimal shrinkage, highly increased structural and mechanical stability, as well as excellent biocompatibility. The hydrogel was produced by ionotropic gelation and reinforced with alumina nanoparticles to form a porous 3D network. In these composite gels, the bacteria Escherichia coli and Bacillus subtilis were embedded. The immobilized bacteria showed high viability and similar metabolic activity as non-embedded cells. Even after repeated glucose consumption cycles, the material maintained high structural stability with stable metabolic activity of the immobilized bacteria. Storing the bionanocomposite for up to 60 days resulted in only minor loss of activity. Accordingly, this approach shows great potential for producing macroscopic bioactive materials for biotechnological processes.

FLO1, FLO5 and FLO11 Flocculation Gene Expression Impacts Saccharomyces cerevisiae Attachment to Penicillium chrysogenum in a Co-immobilization Technique

A reoccurring flaw of most yeast immobilization systems that limits the potential of the technique is leakage of the cells from the matrix. Leakage may be due to weakly adherent cells, deterioration of the matrix, or to new growth and loss of non-adherent daughter cells. Yeast biocapsules are a spontaneous, cost effective system of immobilization whereby Saccharomyces cerevisiae cells are attached to the hyphae of Penicillium chrysogenum, creating hollow spheres that allow recovery and reutilization. This attachment is based on naturally occurring adherent properties of the yeast cell surface. We hypothesized that proteins associated with flocculation might play a role in adherence to fungal hyphae. To test this hypothesis, yeast strains with overexpressed and deleted flocculation genes (FLO1, FLO5, and FLO11) were evaluated for biocapsule formation to observe the impact of gene expression on biocapsule diameter, number, volume, dry mass, and percent immobilized versus non-immobilized cells. Overexpression of all three genes enhanced immobilization and resulted in larger diameter biocapsules. In particular, overexpression of FLO11 resulted in a five fold increase of absorbed cells versus the wild type isogenic strain. In addition, deletion of FLO1 and FLO11 significantly decreased the number of immobilized yeast cells compared to the wild type BY4742. These results confirm the role of natural adherent properties of yeast cells in attachment to fungal hyphae and offer the potential to create strongly adherent cells that will produce adherent progeny thereby reducing the potential for cell leakage from the matrix.

Electrosprayed genipin cross-linked alginate-chitosan microcarriers for ex vivo expansion of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are potential therapeutic candidates, owing to their ability to differentiate into several cell types. However, the gap between availability and demand of MSCs requires alternative expansion methods from 2D culture flasks. Microcarriers are a promising approach for MSC expansion due to their high surface area-to-volume ratio. However, current commercial microcarriers do not provide the highest cell yield due to low cell attachment efficiencies and difficulty in cell detachment. This study developed a hydrogel-based microcarrier from genipin cross-linked alginate-chitosan beads. Alginate beads were produced by electrospraying before being coated with chitosan and cross-linked in genipin. The degree of cross-linking was determined through fluorescence reading of the genipin-chitosan conjugates. MSCs cultured on these microcarriers had a 26% higher cell attachment and twice the proliferation rate compared to the commercial microcarrier Cytodex 1. Cells easily detached from the hydrogel beads and did not require extended incubation periods or intense agitation during cell harvest. There was no significant difference in gene expression between the two microcarriers for the positive MSC surface markers CD-90, CD-105, and CD-73 as well as showing either low or no signal for negative MSC surface markers CD-45 and CD-34. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 122-133, 2019.

Yeast Immobilization Systems for Alcoholic Wine Fermentations: Actual Trends and Future Perspectives

Yeast immobilization is defined as the physical confinement of intact cells to a region of space with conservation of biological activity. The use of these methodologies for alcoholic fermentation (AF) offers many advantages over the use of the conventional free yeast cell method and different immobilization systems have been proposed so far for different applications, like winemaking. The most studied methods for yeast immobilization include the use of natural supports (e.g., fruit pieces), organic supports (e.g., alginate), inorganic (e.g., porous ceramics), membrane systems, and multi-functional agents. Some advantages of the yeast-immobilization systems include: high cell densities, product yield improvement, lowered risk of microbial contamination, better control and reproducibility of the processes, as well as reuse of the immobilization system for batch fermentations and continuous fermentation technologies. However, these methods have some consequences on the behavior of the yeasts, affecting the final products of the fermentative metabolism. This review compiles current information about cell immobilizer requirements for winemaking purposes, the immobilization methods applied to the production of fermented beverages to date, and yeast physiological consequences of immobilization strategies. Finally, a recent inter-species immobilization methodology has been revised, where yeast cells are attached to the hyphae of a Generally Recognized As Safe fungus and remain adhered following loss of viability of the fungus. The bio-capsules formed with this method open new and promising strategies for alcoholic beverage production (wine and low ethanol content beverages).

Technology and potential applications of probiotic encapsulation in fermented milk products

Fermented milk products containing probiotics and prebiotics can be used in management, prevention and treatment of some important diseases (e.g., intestinal- and immune-associated diseases). Microencapsulation has been used as an efficient method for improving the viability of probiotics in fermented milks and gastrointestinal tract. Microencapsulation of probiotic bacterial cells provides shelter against adverse conditions during processing, storage and gastrointestinal passage. Important challenges in the field include survival of probiotics during microencapsulation, stability of microencapsulated probiotics in fermented milks, sensory quality of fermented milks with microencapsulated probiotics, and efficacy of microencapsulation to deliver probiotics and their controlled or targeted release in the gastrointestinal tract. This study reviews the current knowledge, and the future prospects and challenges of microencapsulation of probiotics used in fermented milk products. In addition, the influence of microencapsulation on probiotics viability and survival is reviewed.

Immobilization of Microbes for Bioremediation of Crude Oil Polluted Environments: A Mini Review

Petroleum hydrocarbons are the most common environmental pollutants in the world and oil spills pose a great hazard to terrestrial and marine ecosystems. Oil pollution may arise either accidentally or operationally whenever oil is produced, transported, stored and processed or used at sea or on land. Oil spills are a major menace to the environment as they severely damage the surrounding ecosystems. To improve the survival and retention of the bioremediation agents in the contaminated sites, bacterial cells must be immobilized. Immobilized cells are widely tested for a variety of applications. There are many types of support and immobilization techniques that can be selected based on the sort of application. In this review article, we have discussed the potential of immobilized microbial cells to degrade petroleum hydrocarbons. In some studies, enhanced degradation with immobilized cells as compared to free living bacterial cells for the treatment of oil contaminated areas have been shown. It was demonstrated that immobilized cell to be effective and is better, faster, and can be occurred for a longer period.

Simple and rapid purification of pediocin PA-1 from Pediococcus pentosaceous NCDC 273 suitable for industrial application

The use of pediocins as food additives or drugs requires a simple and rapid method by which large quantities of homogeneous pediocin are produced at industrial level. Two centrifugation steps required during initial stages of purification i.e. separation of cells from fermentation broth and collection of precipitates after ammonium sulphate precipitation are the major bottlenecks for their large scale purification. In the present work, pediocin production by a new a dairy strain, Pediococcus pentosaceous NCDC 273 (identical to pediocin PA-1 at nucleotide sequence level), was found to be optimum at initial pH of 6.0 and 7.0 of basal MRS supplemented with 20 g/l of glucose or lactose at 20 and 24 h, respectively. Immobilization of cells through entrapment in alginate-xanthan gum gel beads with chitosan coating resulted in negligible cell release during fermentation. Thus, the cell free extract was directly collected through decantation, avoiding the need of centrifugation step at this stage. Subsequent ammonium sulphate precipitation at isoelectric point of pediocin PA-1 (8.85), using magnetic stirrer at high speed (approx. 1200 rpm), resulted in forceful deposition of precipitates on the wall of precipitation beaker allowing their collection using a spatula, avoiding centrifugation step at this stage also. Further purification using cation-exchange chromatography resulted in yield of 134.4% with more than 320 fold purification with the specific activity of 19×10⁵ AU/mg. The collection of single peak of pediocin at 41.9min in RP-HPLC, overlapping with standard pediocin PA-1, resulted in yield of 1.15 μg from 20 μl of sample applied. The overlapping of RP-HPLC peak and SDS-PAGE band corresponding to 4.6 kDa, confirmed the purity and identity of pediocin 273 as pediocin PA-1.

Enhanced butyric acid tolerance and bioproduction by Clostridium tyrobutyricum immobilized in a fibrous bed bioreactor

Repeated fed-batch fermentation of glucose by Clostridium tyrobutyricum immobilized in a fibrous bed bioreactor (FBB) was successfully employed to produce butyric acid at a high final concentration as well as to adapt a butyric-acid-tolerant strain. At the end of the eighth fed-batch fermentation, the butyric acid concentration reached 86.9 ± 2.17 g/L, which to our knowledge is the highest butyric acid concentration ever produced in the traditional fermentation process. To understand the mechanism and factors contributing to the improved butyric acid production and enhanced acid tolerance, adapted strains were harvested from the FBB and characterized for their physiological properties, including specific growth rate, acid-forming enzymes, intracellular pH, membrane-bound ATPase and cell morphology. Compared with the original culture used to seed the bioreactor, the adapted culture showed significantly reduced inhibition effects of butyric acid on specific growth rate, cellular activities of butyric-acid-forming enzyme phosphotransbutyrylase (PTB) and ATPase, together with elevated intracellular pH, and elongated rod morphology.

Cell immobilization for production of lactic acid biofilms do it naturally

Interest in natural cell immobilization or biofilms for lactic acid fermentation has developed considerably over the last few decades. Many studies report the benefits associated with biofilms as industrial methods for food production and for wastewater treatment, since the formation represents a protective means of microbial growth offering survival advantages to cells in toxic environments. The formation of biofilms is a natural process in which microbial cells adsorb to a support without chemicals or polymers that entrap the cells and is dependent on the reactor environment, microorganism, and characteristics of the support. These unique characteristics enable biofilms to cause chronic infections, disease, food spoilage, and devastating effects as in microbial corrosion. Their distinct resistance to toxicity, high biomass potential, and improved stability over cells in suspension make biofilms a good tool for improving the industrial economics of biological lactic acid production. Lactic acid bacteria and specific filamentous fungi are the main sources of biological lactic acid. Over the past two decades, studies have focused on improving the lactic acid volumetric productivity through reactor design development, new support materials, and improvements in microbial production strains. To illustrate the operational designs applied to the natural immobilization of lactic acid producing microorganisms, this chapter presents the results of a search for optimum parameters and how they are affected by the physical, chemical, and biological variables of the process. We will place particular emphasis upon the relationship between lactic acid productivity attained by various types of reactors, supports, media formulations, and lactic acid producing microorganisms.

Encapsulated Lactic Acid Bacteria for Control of Malolactic Fermentation in Wine

The kinetics of both malolactic fermentation in Chardonnay wine by encapsulating Lactobacillus casei cells in pectate gel and lyophilized Oenococcus oeni culture has been carried out. The influence of acidity, sulfur dioxide content, and organic acid content on the malolactic activity of the bacteria has been controlled. Encapsulated bacteria degraded 30%, of malic acid in white wine, deacidifying it from pH 3.15 to 3.40, whereas the lyophilized culture degraded 48% of malic acid, deacidifying from pH 3.15 to 3.60. The degree of conversion of malic acid in wine by the encapsulated cells was twice as high as that obtained by the free Lactobacillus casei cells. The operational stability of calcium pectate gel capsules was 6 months. It has been proved that the encapsulated biocatalyst increases the rate of fermentation, and induces the fermentation to take place at high ethanol concentrations. The proposed encapsulated biocatalyst is an attractive material for industrial applications in continuous winemaking processes.

Probiotics, prebiotics, and synbiotics

According to the German definition, probiotics are defined viable microorganisms, sufficient amounts of which reach the intestine in an active state and thus exert positive health effects. Numerous probiotic microorganisms (e.g. Lactobacillus rhamnosus GG, L. reuteri, bifidobacteria and certain strains of L. casei or the L. acidophilus-group) are used in probiotic food, particularly fermented milk products, or have been investigated--as well as Escherichia coli strain Nissle 1917, certain enterococci (Enterococcus faecium SF68) and the probiotic yeast Saccharomyces boulardii--with regard to their medicinal use. Among the numerous purported health benefits attributed to probiotic bacteria, the (transient) modulation of the intestinal microflora of the host and the capacity to interact with the immune system directly or mediated by the autochthonous microflora, are basic mechanisms. They are supported by an increasing number of in vitro and in vivo experiments using conventional and molecular biologic methods. In addition to these, a limited number of randomized, well-controlled human intervention trials have been reported. Well-established probiotic effects are: 1. Prevention and/or reduction of duration and complaints of rotavirus-induced or antibiotic-associated diarrhea as well as alleviation of complaints due to lactose intolerance. 2. Reduction of the concentration of cancer-promoting enzymes and/or putrefactive (bacterial) metabolites in the gut. 3. Prevention and alleviation of unspecific and irregular complaints of the gastrointestinal tracts in healthy people. 4. Beneficial effects on microbial aberrancies, inflammation and other complaints in connection with: inflammatory diseases of the gastrointestinal tract, Helicobacter pylori infection or bacterial overgrowth. 5. Normalization of passing stool and stool consistency in subjects suffering from obstipation or an irritable colon. 6. Prevention or alleviation of allergies and atopic diseases in infants. 7. Prevention of respiratory tract infections (common cold, influenza) and other infectious diseases as well as treatment of urogenital infections. Insufficient or at most preliminary evidence exists with respect to cancer prevention, a so-called hypocholesterolemic effect, improvement of the mouth flora and caries prevention or prevention or therapy of ischemic heart diseases or amelioration of autoimmune diseases (e.g. arthritis). A prebiotic is "a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well being and health", whereas synergistic combinations of pro- and prebiotics are called synbiotics. Today, only bifidogenic, non-digestible oligosaccharides (particularly inulin, its hydrolysis product oligofructose, and (trans)galactooligosaccharides), fulfill all the criteria for prebiotic classification. They are dietary fibers with a well-established positive impact on the intestinal microflora. Other health effects of prebiotics (prevention of diarrhoea or obstipation, modulation of the metabolism of the intestinal flora, cancer prevention, positive effects on lipid metabolism, stimulation of mineral adsorption and immunomodulatory properties) are indirect, i.e. mediated by the intestinal microflora, and therefore less-well proven. In the last years, successful attempts have been reported to make infant formula more breast milk-like by the addition of fructo- and (primarily) galactooligosaccharides.

Semi-continuous xylose-to-xylitol bioconversion by Ca-alginate entrapped yeast cells in a stirred tank reactor

Candida guilliermondii FTI 20037 cells were entrapped in Ca-alginate beads and used for xylose-to-xylitol bioconversions during five successive batches in a stirred tank reactor. Supplemented sugarcane bagasse hemicellulosic hydrolysate was used as the fermentation medium. The average volume of the Ca-alginate beads was reduced by about 30% after the 600 h taken to perform the five bioconversion cycles, thus demonstrating physical instability under the conditions prevailing in the reactor vessel. In spite of this, almost steady bioconversion rates and yields were observed along the repeated batches. In average values, a production of 51.6 g l(-1), a productivity of 0.43 g l(-1 )h(-1) and a yield of 0.71 g g(-1) were attained in each batch, variation coefficients being smaller than 10%.

Production of cellulase by Aspergillus niger biofilms developed on polyester cloth

AIMS

To compare cellulase production by Aspergillus niger ATCC 10864 biofilms on polyester cloth and freely suspended cultures in shaken flasks and microbioreactors of bubble column type.

METHODS AND RESULTS

Both shaken flasks and oxygenated microbioreactors containing 40 ml of production medium were used to compare cellulase secretion by free mycelium and biofilm cultures. Free mycelium cultures grew better in flasks than in microbioreactors producing compact and fluffy pellets, respectively, while the opposite was found for biofilm cultures without any visible change in biofilm morphology. Cellulase activities and volumetric productivities attained by biofilms in flask cultures were 70% higher than that produced by free mycelium cultures and threefold higher when biofilms were grown in microbioreactors.

CONCLUSIONS

Fungal biofilms developed on polyester cloth in both flasks and microbioreactors produce higher cellulase yields and volumetric productivities than free mycelium cultures at lower biomass levels.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results of the present study are of commercial and biological interest. All productivity parameters revealed that fungal biofilms may be used for the production of cellulase and other proteins in various types of bioreactors. Moreover, they may be used as model systems to study differential gene expression related to cell adhesion.

Enhanced propionic acid fermentation by Propionibacterium acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor

Fed-batch fermentations of glucose by P. acidipropionici ATCC 4875 in free-cell suspension culture and immobilized in a fibrous-bed bioreactor (FBB) were studied. The latter produced a much higher propionic acid concentration (71.8 +/- 0.8 g/L vs. 52.2 +/- 1.1 g/L), indicating enhanced tolerance to propionic acid inhibition by cells adapted in the FBB. Compared to the free-cell fermentation, the FBB culture produced 20-59% more propionate (0.40-0.65 +/- 0.02 g/g vs. 0.41 +/- 0.02 g/g), 17% less acetate (0.10 +/- 0.01 g/g vs. 0.12 +/- 0.02 g/g), and 50% less succinate (0.09 +/- 0.02 g/g vs. 0.18 +/- 0.03 g/g) from glucose. The higher propionate production in the FBB was attributed to mutations in two key enzymes, oxaloacetate transcarboxylase and propionyl CoA: succinyl CoA transferase, leading to the production of propionic acid from pyruvate. Both showed higher specific activity and lower sensitivity to propionic acid inhibition in the mutant than in the wild type. In contrast, the activity of PEP carboxylase, which converts PEP directly to oxaloacetate and leads to the production of succinate from glucose, was generally lower in the mutant than in the wild type. For phosphotransacetylase and acetate kinase in the acetate formation pathway, however, there was no significant difference between the mutant and the wild type. In addition, the mutant had a striking change in its morphology. With a threefold increase in its length and approximately 24% decrease in its diameter, the mutant cell had an approximately 10% higher specific surface area that should have made the mutant more efficient in transporting substrates and metabolites across the cell membrane. A slightly lower membrane-bound ATPase activity found in the mutant also indicated that the mutant might have a more efficient proton pump to allow it to better tolerate propionic acid. In addition, the mutant had more longer-chain saturated fatty acids (C17:0) and less unsaturated fatty acids (C18:1), both of which could decrease membrane fluidity and might have contributed to the increased propionate tolerance. The enhanced propionic acid production from glucose by P. acidipropionici was thus attributed to both a high viable cell density maintained in the reactor and favorable mutations resulted from adaptation by cell immobilization in the FBB.

Ethanol production from glucose and dilute-acid hydrolyzates by encapsulatedS. cerevisiae

The performance of encapsulated Saccharomyces cerevisiae CBS 8066 in anaerobic cultivation of glucose, in the presence and absence of furfural as well as in dilute-acid hydrolyzates, was investigated. The cultivation of encapsulated cells in 10 sequential batches in synthetic media resulted in linear increase of biomass up to 106 g/L of capsule volume, while the ethanol productivity remained constant at 5.15 (+/-0.17) g/L x h (for batches 6-10). The cells had average ethanol and glycerol yields of 0.464 and 0.056 g/g in these 10 batches. Addition of 5 g/L furfural decreased the ethanol productivity to a value of 1.31 (+/-0.10) g/L x h with the encapsulated cells, but it was stable in this range for five consecutive batches. On the other hand, the furfural decreased the ethanol yield to 0.41-0.42 g/g and increased the yield of acetic acid drastically up to 0.068 g/g. No significant lag phase was observed in any of these experiments. The encapsulated cells were also used to cultivate two different types of dilute-acid hydrolyzates. While the free cells were not able to ferment the hydrolyzates within at least 24 h, the encapsulated yeast successfully converted glucose and mannose in both of the hydrolyzates in less than 10 h with no significant lag phase. However, since the hydrolyzates were too toxic, the encapsulated cells lost their activity gradually in sequential batches.

Development of acetylcholinesterase silica sol–gel immobilized biosensor—an application towards oxydemeton methyl detection

An amperometric silica sol-gel film immobilized biosensor doped with acetylcholinesterase was fabricated in the laboratory finding application in organophosphate detection based on enzyme inhibition. The substrate used was acetylthiocholine chloride and thiocholine released from the enzymatic hydrolysis was electrochemically oxidized giving larger anodic current at 0.5-0.6 V (versus Ag/AgCl reference). The dependencies of the current response on pH, enzyme loading and thermal stability of the developed biosensor were evaluated. The analytical performance of enzyme electrode towards substrate and inhibitor was investigated. Oxydemeton methyl was taken as a model compound for the inhibition studies. Linear calibration for oxydemeton methyl was obtained in the range of 2-200 ppb under the optimized conditions following an incubation time of 20 min. Treatment of the inhibited enzyme with pyridine-2-aldehyde restored 92% of its original activity. The sensor stored at -20 degrees C had a good storage and operational stability retaining 85% of its original activity for 60 successive measurements.