Modified Activated Carbon: A Supporting Material for Improving Clostridium beijerinckii TISTR1461 Immobilized Fermentation

This study aimed to investigate the effect of activated carbon (AC) as an immobilization material in acetone-butanol-ethanol fermentation. The AC surface was modified with different physical (orbital shaking and refluxing) and chemical (nitric acid, sodium hydroxide and, (3-aminopropyl)triethoxysilane (APTES)) treatments to enhance the biobutanol production by Clostridium beijerinckii TISTR1461. The effect of surface modification on AC was evaluated using Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, surface area analyses, and X-ray photoelectron spectroscopy, while the fermented broth was examined by high-performance liquid chromatography. The chemical functionalization significantly modified the physicochemical properties of the different treated ACs and further enhanced the butanol production. The AC treated with APTES under refluxing provided the best fermentation results at 10.93 g/L of butanol, 0.23 g/g of yield, and 0.15 g/L/h of productivity, which were 1.8-, 1.5-, and 3.0-fold higher, respectively, than that in the free-cell fermentation. The obtained dried cell biomass also revealed that the treatment improved the AC surface for cell immobilization. This study demonstrated and emphasized the importance of surface properties to cell immobilization.

Preparation of Hybrid Sol-Gel Materials Based on Living Cells of Microorganisms and Their Application in Nanotechnology

Microorganism-cell-based biohybrid materials have attracted considerable attention over the last several decades. They are applied in a broad spectrum of areas, such as nanotechnologies, environmental biotechnology, biomedicine, synthetic chemistry, and bioelectronics. Sol-gel technology allows us to obtain a wide range of high-purity materials from nanopowders to thin-film coatings with high efficiency and low cost, which makes it one of the preferred techniques for creating organic-inorganic matrices for biocomponent immobilization. This review focuses on the synthesis and application of hybrid sol-gel materials obtained by encapsulation of microorganism cells in an inorganic matrix based on silicon, aluminum, and transition metals. The type of immobilized cells, precursors used, types of nanomaterials obtained, and their practical applications were analyzed in detail. In addition, techniques for increasing the microorganism effective time of functioning and the possibility of using sol-gel hybrid materials in catalysis are discussed.

Colonization versus encapsulation in cell-laden materials design: porosity and process biocompatibility determine cellularization pathways

Seeding materials with living cells has been-and still is-one of the most promising approaches to reproduce the complexity and the functionality of living matter. The strategies to associate living cells with materials are limited to cell encapsulation and colonization, however, the requirements for these two approaches have been seldom discussed systematically. Here we propose a simple two-dimensional map based on materials' pore size and the cytocompatibility of their fabrication process to draw, for the first time, a guide to building cellularized materials. We believe this approach may serve as a straightforward guideline to design new, more relevant materials, able to seize the complexity and the function of biological materials. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

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.

The physics and chemistry of silica-in-silicates nanocomposite hydrogels and their phycocompatibility

Silicates-in-silica nanocomposite hydrogels obtained from sodium silicates/colloidal silica mixtures have previously been found to be useful for bacterial encapsulation. However the extension of synthesis conditions and the understanding of their impact on the silica matrix would widen the applicability of this process in terms of encapsulated organisms and the host properties. Here the influence of silicates and the colloidal silica concentration as well as pH conditions on the gel time, the optical properties, the structural and mechanical properties of silica matrices was studied. We show that gel formation is driven by silicate condensation but that the aggregation of silica colloids also has a major influence on the transparency and structure of the nanocomposites. Three different photosynthetic organisms, cyanobacteria Anabaena flos-aquae and two microalgae Chorella vulgaris and Euglena gracilis, were used as probes of the phycocompatibility of the process. The three organisms were highly sensitive to the silicate concentration, which impacts both the gelation time and ionic strength conditions. The Ludox content was crucial for cyanobacteria as it strongly impacts the Young's modulus of the matrices. The detrimental effect of acidic pH on cell suspension was compensated by the silica network. Overall, it is now possible to select optimal encapsulation conditions based on the physiology of the targeted cells, opening wide perspectives for the design of biosensors and bioreactors.

Microorganism mediated biosynthesis of metal chalcogenides; a powerful tool to transform toxic effluents into functional nanomaterials

Cadmium contained in soil and water can be taken up by certain crops and aquatic organisms and accumulate in the food-chain, thus removal of Cd from mining or industrial effluents - i.e. Ni-Cd batteries, electroplating, pigments, fertilizers - becomes mandatory for human health. In parallel, there is an increased interest in the production of luminescent Q-dots for applications in bioimaging, sensors and electronic devices, even the present synthesis methods are economic and environmentally costly. An alternative green pathway for producing Metal chalcogenides (MC: CdS, CdSe, CdTe) nanocrystals is based on the metabolic activity of living organisms. Intracellular and extracellular biosynthesis of can be achieved within a biomimetic approach feeding living organisms with Cd precursors providing new routes for combining bioremediation with green routes for producing MC nanoparticles. In this mini-review we present the state-of-the-art of biosynthesis of MC nanoparticles with a critical discussion of parameters involved and protocols. Few existing examples of scaling-up are also discussed. A modular reactor based on microorganisms entrapped in biocompatible mineral matrices - already proven for bioremediation of dissolved dyes - is proposed for combining both Cd-depletion and MC nanoparticle's production.

S-Layer-Based Nanocomposites for Industrial Applications

This chapter covers the fundamental aspects of bacterial S-layers: what are S-layers, what is known about them, and what are their main features that makes them so interesting for the production of nanostructures. After a detailed introduction of the paracrystalline protein lattices formed by S-layer systems in nature the chapter explores the engineering of S-layer-based materials. How can S-layers be used to produce "industry-ready" nanoscale bio-composite materials, and which kinds of nanomaterials are possible (e.g., nanoparticle synthesis, nanoparticle immobilization, and multifunctional coatings)? What are the advantages and disadvantages of S-layer-based composite materials? Finally, the chapter highlights the potential of these innovative bacterial biomolecules for future technologies in the fields of metal filtration, catalysis, and bio-functionalization.

Polymer-immobilized ready-to-use recombinant yeast assays for the detection of endocrine disruptive compounds

Recombinant yeast assays (RYAs) constitute a suitable tool for the environmental monitoring of compounds with endocrine disrupting activities, notably estrogenicity and androgenicity. Conventional procedures require yeast reconstitution from frozen stock, which usually takes several days and demands additional equipment. With the aim of applying such assays to field studies and making them more accessible to less well-equipped laboratories, we have optimized RYA by the immobilization of Saccharomyces cerevisiae cells in three different polymer matrices - gelatin, Bacto agar, and Yeast Extract Peptone Dextrose agar - to obtain a ready-to-use version for the fast assessment of estrogenic and androgenic potencies of compounds and environmental samples. Among the three matrices, gelatin showed the best results for both testosterone (androgen receptor yeast strain; AR-RYA) and 17β-estradiol (estrogen receptor yeast strain; ER-RYA). AR-RYA was characterized by a lowest observed effect concentration (LOEC), EC50 and induction factor (IF) of 1nM, 2.2nM and 51, respectively. The values characterizing ER-RYA were 0.4nM, 1.8nM, and 63, respectively. Gelatin immobilization retained yeast viability and sensitivity for more than 90d of storage at 4°C. The use of the immobilized yeast reduced the assay duration to only 3h without necessity of sterile conditions. Because immobilized RYA can be performed either in multiwell microplates or glass tubes, it allows multiple samples to be tested at once, and easy adaptation to existing portable devices for direct in-field applications.

Porous inorganic materials from living porogens: channel-like TiO2 from yeast-assisted sol-gel process

Vitality of yeast cells maintained in an aqueous sol-gel solution containing titanium tetraisopropoxide and glucose. The living cells and their metabolites acted as the porogens for a channel-like TiO2 precursor. Further processing of the precursor offered a channel-like meso/macroporous TiO2, a potential anode material for Li-ion battery.

Engineering Cellular Photocomposite Materials Using Convective Assembly

Fabricating industrial-scale photoreactive composite materials containing living cells, requires a deposition strategy that unifies colloid science and cell biology. Convective assembly can rapidly deposit suspended particles, including whole cells and waterborne latex polymer particles into thin (<10 µm thick), organized films with engineered adhesion, composition, thickness, and particle packing. These highly ordered composites can stabilize the diverse functions of photosynthetic cells for use as biophotoabsorbers, as artificial leaves for hydrogen or oxygen evolution, carbon dioxide assimilation, and add self-cleaning capabilities for releasing or digesting surface contaminants. This paper reviews the non-biological convective assembly literature, with an emphasis on how the method can be modified to deposit living cells starting from a batch process to its current state as a continuous process capable of fabricating larger multi-layer biocomposite coatings from diverse particle suspensions. Further development of this method will help solve the challenges of engineering multi-layered cellular photocomposite materials with high reactivity, stability, and robustness by clarifying how process, substrate, and particle parameters affect coating microstructure. We also describe how these methods can be used to selectively immobilize photosynthetic cells to create biomimetic leaves and compare these biocomposite coatings to other cellular encapsulation systems.

Inorganic materials using 'unusual' microorganisms

A promising avenue of research in materials science is to follow the strategies used by Mother Nature to fabricate ornate hierarchical structures as exemplified by organisms such as diatoms, sponges and magnetotactic bacteria. Some of the strategies used in the biological world to create functional inorganic materials may well have practical implications in the world of nanomaterials. Therefore, the strive towards exploring nature's ingenious work for designing strategies to create inorganic nanomaterials in our laboratories has led to development of biological and biomimetic synthesis routes over the past decade or so. A large proportion of these relentless efforts have explored the use of those microorganisms, which are typically not known to encounter these inorganic materials in their natural environment. Therefore, one can consider these microorganisms as 'unusual' for the purpose for which they have been utilized - it is in this context that this review has been penned down. In this extensive review, we discuss the use of these 'unusual' microorganisms for deliberate biosynthesis of various nanomaterials including biominerals, metals, sulfides and oxides nanoparticles. In addition to biosynthesis approach, we have also discussed a bioleaching approach, which can provide a noble platform for room-temperature synthesis of inorganic nanomaterials using naturally available raw materials. Moreover, the unique properties and functionalities displayed by these biogenic inorganic materials have been discussed, wherever such properties have been investigated previously. Finally, towards the end of this review, we have made efforts to summarize the common outcomes of the biosynthesis process and draw conclusions, which provide a perspective on the current status of the biosynthesis research field and highlights areas where future research in this field should be directed to realize the full potential of biological routes towards nanomaterials synthesis. Furthermore, the review clearly demonstrates that the biological route to inorganic materials synthesis is not merely an addition to the existing list of synthesis routes; biological routes using 'unusual' microorganisms might in fact provide an edge over other nanomaterials synthesis routes in terms of their eco-friendliness, low energy intensiveness, and economically-viable synthesis. This review has significant importance for colloids and interface science since it underpins the synthesis of colloidal materials using 'unusual' microorganism, wherein the role of biological interfaces for controlled synthesis of technologically important nanomaterials is clearly evident.

Scaling up of ethanol production from sugar molasses using yeast immobilized with alginate-based MCM-41 mesoporous zeolite composite carrier

Microporous and mesoporous zeolites, including ZSM-5, H-β, H-Y, and MCM-41, were modified with 3-aminopropyl-triethoxysilane (APTES), then inorganic fillers, such as abovementioned zeolites or mesoporous materials, (α-AlOOH or γ-Al(2)O(3)), were mixed with alginate embedded with yeast; and finally these carriers were cross-linked through the double oxirane. The alginate-based immobilized yeast with MCM-41 exhibited much shorter fermentation time and higher ethanol concentration than pure alginate and other composite carriers with the highest cell concentration of 4.8×10(9) cells/mL. The composite carrier maintains the highest ethanol productivity of 6.55 g/L/h for 60 days in continuous fermentation process, implying good operational durability for commercial applications. The reason for the higher bio-catalytical function of the immobilized yeast might lay in the uniformly yeast distribution in the bio-reactor and high yeast cell concentration, which contributed by the improved transmission of fermentation media and combined effects of yeast adsorption by MCM-41 and embedment by alginate.

From diatoms to silica-based biohybrids

Diatom inspired bio-hybrids offer new possibilities for the synthesis of nanostructured materials and the development of nanomedicine.

Remediation of waters contaminated with MCPA by the yeasts Lipomyces starkeyi entrapped in a sol-gel zirconia matrix

A single-stage sol-gel route was set to entrap yeast cells of Lipomyces starkeyi in a zirconia (ZrO(2)) matrix, and the remediation ability of the resulting catalyst toward a phenoxy acid herbicide, 4-chloro-2-methylphenoxyacetic acid (MCPA), was studied. It was found that the experimental procedure allowed a high dispersion of the microorganisms into the zirconia gel matrix; the ZrO(2) matrix exhibited a significant sorption capacity of the herbicide, and the entrapped cells showed a degradative activity toward MCPA. The combination of these effects leads to a nearly total removal efficiency (>97%) of the herbicide at 30 °C within 1 h incubation time from a solution containing a very high concentration of MCPA (200 mg L(-1)). On the basis of the experimental evidence, a removal mechanism was proposed involving in the first step the sorption of the herbicide molecules on the ZrO(2) matrix, followed by the microbial degradation operated by the entrapped yeasts, the metabolic activity of which appear enhanced under the microenvironmental conditions established within the zirconia matrix. Repeated batch tests of sorption/degradation of entrapped Lipomyces showed that the removal efficiency retained almost the same value of 97.3% after 3 batch tests, with only a subsequent slight decrease, probably due to the progressive saturation of the zirconia matrix.

How to design cell-based biosensors using the sol-gel process

Inorganic gels formed using the sol-gel process are promising hosts for the encapsulation of living organisms and the design of cell-based biosensors. However, the possibility to use the biological activity of entrapped cells as a biological signal requires a good understanding and careful control of the chemical and physical conditions in which the organisms are placed before, during, and after gel formation, and their impact on cell viability. Moreover, it is important to examine the possible transduction methods that are compatible with sol-gel encapsulated cells. Through an updated presentation of the current knowledge in this field and based on selected examples, this review shows how it has been possible to convert a chemical technology initially developed for the glass industry into a biotechnological tool, with current limitations and promising specificities.

Insight into cellular response of plant cells confined within silica-based matrices

The encapsulation of living plant cells into materials could offer the possibility to develop new green biochemical technologies. With the view to designing new functional materials, the physiological activity and cellular response of entrapped cells within different silica-based matrices have been assessed. A fine-tuning of the surface chemistry of the matrix has been achieved by the in situ copolymerization of an aqueous silica precursor and a biocompatible trifunctional silane bearing covalently bound neutral sugars. This method allows a facile control of chemical and physical interactions between the entrapped plant cells and the scaffold. The results show that the cell-matrix interaction has to be carefully controlled in order to avoid the mineralization of the cell wall which typically reduces the bioavailability of nutrients. Under appropriate conditions, the introduction of a trifunctional silane (ca. 10%) during the preparation of hybrid gels has shown to prolong the biological activity as well as the cellular viability of plant cells. The relations of cell behavior with some other key factors such as the porosity and the contraction of the matrix are also discussed.

Advances in biomimetic and nanostructured biohybrid materials

The rapid increase of interest in the field of biohybrid and biomimetic materials that exhibit improved structural and functional properties is attracting more and more researchers from life science, materials science, and nanoscience. Concomitant results offer valuable opportunities for applications that involve disciplines dealing with engineering, biotechnology, medicine and pharmacy, agriculture, nanotechnology, and others. In the current contribution we collect recent illustrative examples of assemblies between materials of biological origin and inorganic solids of different characteristics (texture, structure, and particle size). We introduce here a general overview on strategies for the preparation and conformation of biohybrids, the synergistic effects that determine the final properties of these materials, and their diverse applications, which cover areas as different as tissue engineering, drug delivery systems, biosensing devices, biocatalysis, green nanocomposites, etc.

Organic-inorganic hybrid material for the cells immobilization: long-term viability mechanism and application in BOD sensors

In this paper, organic-inorganic hybrid material, which is composed of silica and the grafting copolymer of poly (vinyl alcohol) and 4-vinylpyridine (PVA-g-P(4-VP)), was employed to immobilize Trichosporon cutaneum strain 2.570 cells. Cells entrapped into the hybrid material were found to keep a long-term viability. The mechanism of such a long-term viability was investigated by using confocal laser scanning microscopy (CLSM). Our studies revealed that arthroconidia produced in the extracellular material might play an important role in keeping the long-term viability of the immobilized microorganism. After the arthroconidia were activated, an electrochemical biochemical oxygen demand (BOD) sensor based on cell/hybrid material-modified supporting membrane was constructed for verifying the proposed mechanism. The results and insight gained from the present experiments can be widely used to various biosensor designs.

Cell-directed assembly of bio/nano interfaces-a new scheme for cell immobilization

When lipid-directed assembly of silicic acid precursors is conducted in the presence of living cells, the cells intervene, surrounding themselves with a fluid, multilayered lipid vesicle that interfaces coherently with an ordered silica mesophase. This bio/nano interface is unique in that its uniform nanostructure prevents excessive drying of water, maintaining cell viability, yet provides accessibility of the cell surface to small molecules. In comparison to existing immobilization schemes, such as encapsulation within sol-gel matrices, we show this interface to form by an active interplay between the living cell and surrounding matrix, which we refer to as cell-directed assembly (CDA). Importantly and perhaps uniquely, CDA creates a localized nanostructured microenvironment within which three-dimensional chemical gradients are established and maintained.

Aqueous silicates in biological sol-gel applications: new perspectives for old precursors

Identification of silica sol-gel chemistry with silicon alkoxide hydrolysis and condensation processes is common in modern materials science. However, aqueous silicates exhibit several features indicating that they may be more suitable precursors for specific fields of research and applications related to biology and medicine. In this Account, we illustrate the potentialities of such aqueous precursors for biomimetic studies, bio-hybrid material design, and bioencapsulation routes. We emphasize that the natural relevance, the biocompatibility, and the low ecological impact of silicate chemistry may balance its lack of diversity, flexibility, and processability.

Plant cell proliferation inside an inorganic host

In recent years, much attention has been paid to plant cell culture as a tool for the production of secondary metabolites and the expression of recombinant proteins. Plant cell immobilization offers many advantages for biotechnological processes. However, the most extended matrices employed, such as calcium-alginate, cannot fully protect entrapped cells. Sol-gel chemistry of silicates has emerged as an outstanding strategy to obtain biomaterials in which living cells are truly protected. This field of research is rapidly developing and a large number of bacteria and yeast-entrapping ceramics have already been designed for different applications. But even mild thermal and chemical conditions employed in sol-gel synthesis may result harmful to cells of higher organisms. Here we present a method for the immobilization of plant cells that allows cell growth at cavities created inside a silica matrix. Plant cell proliferation was monitored for a 6-month period, at the end of which plant calli of more than 1 mm in diameter were observed inside the inorganic host. The resulting hybrid device had good mechanical stability and proved to be an effective barrier against biological contamination, suggesting that it could be employed for long-term plant cell entrapment applications.