Alginate as a Carrier for Cell Immobilisation. In: Nedović V, Willaert R, editors. Fundamentals of Cell Immobilisation Biotechnology. Dordrecht: Springer Netherlands; 2004. pp. 33-51. [DOI: 10.1007/978-94-017-1638-3_2]

Enhancing bioprocessing of red pigment from immobilized culture of gamma rays mutant of the endophytic fungus Monascus ruber SRZ112

Considerable attention has been paid to exploring the biotechnological applications of several Monascus sp. for pigment production. In this study, our focus is on enhancing the bioprocessing of red pigment (RP) derived from the endophytic fungus Monascus ruber SRZ112. To achieve this, we developed a stable mutant strain with improved productivity through gamma irradiation. This mutant was then employed in the immobilization technique using various entrapment carriers. Subsequently, we optimized the culture medium for maximal RP production using the Response Surface Methodology. Finally, these immobilized cultures were successfully utilized for RP production using a semi-continuous mode of fermentation. After eight cycles of fermentation, the highest RP yield by immobilized mycelia reached 309.17 CV mL-1, a significant increase compared to the original titer. Importantly, this study marks the first report on the successful production of Monascus RP in a semi-continuous mode using gamma rays' mutant strain, offering prospects for commercial production.

Alginate-Based 3D A549 Cell Culture Model to Study Paracoccidioides Infection

A three-dimensional (3D) lung aggregate model based on sodium alginate scaffolds was developed to study the interactions between Paracoccidioides brasiliensis (Pb) and lung epithelial cells. The suitability of the 3D aggregate as an infection model was examined using cell viability (cytotoxicity), metabolic activity, and proliferation assays. Several studies exemplify the similarity between 3D cell cultures and living organisms, which can generate complementary data due to the greater complexity observed in these designed models, compared to 2D cell cultures. A 3D cell culture system of human A549 lung cell line plus sodium alginate was used to create the scaffolds that were infected with Pb18. Our results showed low cytotoxicity, evidence of increased cell density (indicative of cell proliferation), and the maintenance of cell viability for seven days. The confocal analysis revealed viable yeast within the 3D scaffold, as demonstrated in the solid BHI Agar medium cultivation. Moreover, when ECM proteins were added to the alginate scaffolds, the number of retrieved fungi was significantly higher. Our results highlight that this 3D model may be promising for in vitro studies of host-pathogen interactions.

Haloferax volcanii for biotechnology applications: challenges, current state and perspectives

Haloferax volcanii is an obligate halophilic archaeon with its origin in the Dead Sea. Simple laboratory culture conditions and a wide range of genetic tools have made it a model organism for studying haloarchaeal cell biology. Halophilic enzymes of potential interest to biotechnology have opened up the application of this organism in biocatalysis, bioremediation, nanobiotechnology, bioplastics and the biofuel industry. Functionally active halophilic proteins can be easily expressed in a halophilic environment, and an extensive genetic toolkit with options for regulated protein overexpression has allowed the purification of biotechnologically important enzymes from different halophiles in H. volcanii. However, corrosion mediated damage caused to stainless-steel bioreactors by high salt concentrations and a tendency to form biofilms when cultured in high volume are some of the challenges of applying H. volcanii in biotechnology. The ability to employ expressed active proteins in immobilized cells within a porous biocompatible matrix offers new avenues for exploiting H. volcanii in biotechnology. This review critically evaluates the various application potentials, challenges and toolkits available for using this extreme halophilic organism in biotechnology.

Formulation strategies for achieving high delivery efficiency of thymoquinone-containing Nigella sativa extract to the colon based on oral alginate microcapsules for treatment of inflammatory bowel disease

Nigella sativa extract (NSE) was incorporated in alginate microcapsules using aerosolisation and homogenisation methods, respectively, with the aim of delivering high concentrations of the active species, thymoquinone (TQ), directly to sites of inflammation in the colon following oral administration. Encapsulation of NSE was accomplished either by direct loading or diffusion into blank microparticles. Microcapsules in the size range 40-60 µm exhibited significantly higher NSE loading up to 42% w/w and encapsulation efficiency (EE) up to 63% when the extract was entrapped by direct encapsulation compared with 4.1 w/w loading, 6.2% EE when NSE was incorporated by diffusion loading. Sequential exposure of samples to simulated intestinal fluids (SIFs) revealed that the microcapsules suppressed NSE release in simulated gastric fluid (SGF) for 2 h and SIF for 4 h and liberated most of the NSE content (80%) in simulated colonic fluid (SCF) over 18 h. NSE released in SCF at 12 h exhibited antioxidant activity, when measured using the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assay at levels comparable with the activity of unencapsulated extract. These findings demonstrate the potential of oral alginate microcapsules as highly efficient, targeted carriers for colonic delivery of NSE in the treatment of inflammatory bowel disease.

Haloferax volcanii as immobilised whole cell biocatalyst: new applications for halophilic systems

Enzyme-mediated synthesis of pharmaceutical compounds is a 'green' alternative to traditional synthetic chemistry, and microbial engineering opens up the possibility of using whole cells as mini-factories. Whole-cell biocatalysis reduces cost by eliminating expensive enzyme purification and cofactor addition steps, as well as resulting in increased enzyme stability. Haloferax volcanii is a model halophilic archaeon encoding highly salt and organic solvent tolerant enzymes such as alcohol dehydrogenase (HvADH2), which catalyses the reduction of aldehydes and ketone in the presence of NADPH/NADH cofactor. A H. volcanii strain for constitutive HvADH2 expression was generated using a strong synthetic promoter (p.syn). The strain was immobilised in calcium alginate beads and repeatedly used as a whole-cell biocatalyst. The reduction of acetophenone, used as test substrate, was very successful and high yields were detected from immobilised whole cells over repeated biotransformation cycles. The immobilised H. volcanii retained stability and high product yields after 1 month of storage at room temperature. This newly developed system offers halophilic enzyme expression in its native environment, high product yield, stability and reusability without the addition of any expensive NADPH/NADH cofactor. This is the first report of whole cell-mediated biocatalysis by the halophilic archaeon H. volcanii.

Alginate-Encapsulated Bacteria for the Treatment of Hypersaline Solutions in Microbial Fuel Cells

A microbial fuel cell (MFC) based on a new wild-type strain of Salinivibrio sp. allowed the self-sustained treatment of hypersaline solutions (100 g L-1 , 1.71 m NaCl), reaching a removal of (87±11) % of the initial chemical oxygen demand after five days of operation, being the highest value achieved for hypersaline MFC. The degradation process and the evolution of the open circuit potential of the MFCs were correlated, opening the possibility for online monitoring of the treatment. The use of alginate capsules to trap bacterial cells, increasing cell density and stability, resulted in an eightfold higher power output, together with a more stable system, allowing operation up to five months with no maintenance required. The reported results are of critical importance to efforts to develop a sustainable and cost-effective system that treats hypersaline waste streams and reduces the quantity of polluting compounds released.

Highly Efficient Malolactic Fermentation of Red Wine Using Encapsulated Bacteria in a Robust Biocomposite of Silica-Alginate

Bacteria encapsulation to develop malolactic fermentation emerges as a biotechnological strategy that provides significant advantages over the use of free cells. Two encapsulation methods have been proposed embedding Oenococcus oeni, (i) interpenetrated polymer networks of silica and Ca-alginate and (ii) Ca-alginate capsules coated with hydrolyzed 3-aminopropyltriethoxysilane (hAPTES). On the basis of our results, only the first method was suitable for bacteria encapsulation. The optimized silica-alginate capsules exhibited a negligible bacteria release and an increase of 328% and 65% in L-malic acid consumption and mechanical robustness, respectively, compared to untreated alginate capsules. Moreover, studies of capsule stability at different pH and ethanol concentrations in water solutions and in wine indicated a better behavior of silica-alginate capsules than untreated ones. The inclusion of silicates and colloidal silica in alginate capsules containing O. oeni improved markedly their capacity to deplete the levels of L-malic acid in red wines and their mechanical robustness and stability.

Nonlinear Dynamics of Brewing Yeast Cell Growth in Alginate Micro-Beads

The nonlinear dynamics of brewing yeast cell growth in porous Ca-alginate matrices is considered experimentally and theoretically. The applications of alginate matrices include the reduction of internal mass transfer resistance, minimized cell leakage and growth restriction due to interactions between matrices and cell membranes comparatively to free cell culture conditions. The effects of micro-bead diameters in the range 0.3-2.0 mm on yeast cell growth were investigated. The stochastic mathematical model from the Langevin class is proposed for the interpretation of cell growth, affected by four micro-processes: micro-environmental quality changes due to nutrient diffusion into the micro-beads, cell leakage, repulsive interactions between boundary layers around the cells themselves, which contribute to the dynamics of cell growth as a negative, nonlinear feedback restriction and random kinetics effects. Such a model is used for the prediction of the optimal diameter of micro-beads, which ensures maximal final cell concentration. The results of cell growth in alginate matrices study have indicated an optimal diameter of 0.5-0.6 mm for micro-beads. Immobilized cells in these beads were not restricted significantly by mass transfer of nutrients and by cell leakage. The highest final cell concentration value indicated the largest feed-back restriction quantified by the constitutive parameter b.

Immobilization of cells by electrostatic droplet generation: a model system for potential application in medicine

The process of electrostatic extrusion as a method for cell immobilization was investigated that could be used for potential applications in medicine. An attempt was made to assess the effects of cell addition and polymer concentration on the overall entrapment procedure, ie, on each stage of immobilization: polymer-cell suspension rheological characteristics, electrostatic extrusion process, and the process ofgelation. The findings should contribute to a better understanding of polymer-cell interactions, which could be crucial in possible medical treatments. Alginate-yeast was used as a model system for carrier-cells. The electrostatic extrusion was considered as a complex two-phase flow system and the effects of cell and alginate concentrations on the resulting microbead size and uniformity were assessed. Under investigated conditions, microbeads 50-600 microm in diameter were produced and the increase in both alginate and cell concentrations resulted in larger microbeads with higher standard deviations in size. We attempted to rationalize the findings by rheological characterization of the cell-alginate suspensions. Rheological characterization revealed non-Newtonian, pseudoplastic behavior of cell-alginate suspensions with higher viscosities at higher alginate concentrations. However, the presence of cells even at high concentrations (5x10(8) and 1x10(9) cells/mL) did not significantly affect the rheological properties of Na-alginate solution. Lastly, we investigated the kinetics of alginate gelation with respect to the quantity of Ca2+ ions and cell presence. The gelation kinetics were examined under conditions of limited supply with Ca2+ ions, which can be essential for immobilization of highly sensitive mammalian cells that require minimal exposure to CaCl2 solution. The molar ratio of G units to Ca2+ ions of 3.8:1 provided complete crosslinking, while the increase in alginate concentration resulted in prolonged gelation times but higher strength of the resulting gel. The cell presence decreased the rate of network formation as well as the strength of the obtained Ca-alginate hydrogel.

Alginate Microbeads as Potential Support for Cultivation of Bone Marrow Stromal Cells

Alginate is currently being employed and explored for a broad range of biomedical and biotechnology applications, due to its biodegradability and simple procedure for cell immobilization. However, cell immobilization was mostly aimed for immunoisolatory and biochemical processing applications and far less is known about potentials of alginate as a substrate for tissue formation. In the present work, isolation, immobilization and cultivation procedures of murine bone marrow stromal cells (BMSC) were studied and standardized in order to establish the alginate-bioreactor culture system for chondrogenic and/or hematopoiesis-supportive tissue progression. Two techniques for cell immobilization based on alginate were investigated: entrapment within gel matrix using electrostatic droplet generation and simple cell adsorption onto gel surfaces. Alginate gels in forms of microbeads and discs with immobilized culture expanded BMSC were cultivated for up to 30 days and analyzed for surface properties, cell concentration, viability, and differentiation.