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Xylitol is a high value polyalcohol being used in pharmaceutical, hygiene, and food products due to its functional properties such as anticariogenic, antibacterial as well as low calorie and low glycemic properties. An alternative route for xylitol production is the biotechnological method in which microorganisms or enzymes are involved as catalysts to convert xylose into xylitol under mild conditions of pressure and temperature. This method is unlike the conventional chemical method that requires high pressure and temperature and results in low product yield. The goal of this research is to employ an integrated process using all fractions of an agro-industrial biomass (oat hull) for xylitol bioproduction, preferably in a repeated batch bioconversion process, with C. guilliermondii as the biocatalyst. Processes including hydrolysis, biomass delignification, hydrolysate detoxification using adsorption process, and finally free- and immobilized-cell bioconversions were employed in this study. The kinetics of acid-catalyzed hydrolysis of hemicellulose was investigated under mild conditions (temperature: 110ºC to 130ºC and catalyst (H2SO4) concentrations from 0.1 to 0.55 N) to determine the kinetic mechanism and generation of monosaccharides (xylose, glucose, and arabinose) as well as the microbial inhibitors consisting of acetic acid, furfural, and hydroxymethylfurfural (HMF) in the hydrolysate. A maximum recovery of 80% was attained for xylose as the main monosaccharide and the substrate for xylitol; its generation in the hydrolysate followed a single-phase 2-step kinetic mechanism similar to that of the HMF. However, a single-phase mechanism with no decomposition could describe the formation of arabinose, acetic acid, and furfural. Glucose generation followed a biphasic mechanism (fast and slow releasing) apparently with no decomposition. In the alkaline delignification of the hydrolysis byproduct (solid fraction) and the intact (crude) biomass, kinetic models based on biphasic mechanism consisting of bulk and terminal phases gave the best results and fit to the experimental data. In the bulk phase, where the temperature ranged from 30ºC to 100ºC, the reaction rate constant varied from 0.15 to 0.19 1/min for the intact biomass and from 0.25 to 0.55 1/min for the hydrolysis byproduct. According to the models, accelerated lignin removal with the increased operating temperature could be due to the shift of the process from the terminal phase to the bulk phase. The values obtained for the activation energies herein ( 33 kJ/mol) were less than the values reported in the literature for other lignocellulosic materials. The removal or reduction of the microbial inhibitors in the medium was carried out by activated carbon (adsorptive detoxification). According to the results using the Langmuir model with the activated carbon as the adsorbent, the maximum monolayer capacities of 341, 211, and 46 mg/g were obtained, respectively, for phenol, furfural, and acetic acid. Thermodynamic analyses indicated that the adsorption of the three abovementioned chemicals by the activated carbon was exothermic (enthalpy: H0), spontaneous (free energy: G0), and based on the affinity of the solute toward the adsorbent (entropy: S0). In the concentrated hydrolysate, the removal of phenols, as the main inhibitor, was very successful such that by activated carbon doses of 1.25%, 2.5%, and 5% (w/v) they could be reduced to 34%, 13%, and 3% of the initial concentration (8.7 g/l), respectively. During xylitol bioproduction process in the repeated batch mode using C. guilliermondii, variables of pH control, medium supplementation, and cell recycling proved to be more important than medium detoxification. Processes involving pH-controlled condition combined with nitrogen supplementation and a mild detoxification performed very well with consistent conversion parameters in the successive batches; values of over 0.8 g/g, 0.55 g/l/h, and 53 g/l were obtained respectively for xylitol yield, volumetric productivity, and final concentration. On the other hand, in a single-batch bioconversion, there was no need for supplementing the medium with the nitrogen source. Kinetic modeling of the process showed that substrate (xylose) as well as co-substrate (glucose) consumption, product (xylitol) formation, and cell regeneration could be predicted by a diauxic model. In the aerated free-cell and immobilized-cell systems, aeration rates of 1.25 vvm and 1.25-1.5 vvm were required for free-cell and immobilized-cell systems, respectively, to reach the maximum bioconversion performance. In the immobilized-cell system, cell support also played an important role in this biotransformation. Application of the support based on the delignified hydrolysis byproduct resulted in high and consistent bioconversion parameters in all batches comparable to the ones in the free-cell system. However, bioconversions using the lignin-rich material (hydrolysis byproduct) resulted in a lower efficiency in the first batch which could be partly improved in the second batch and almost fully increased in the third batch to nearly reach performance parameters comparable to the ones obtained in the free-cell system. Overall, the integrated process employed in this investigation helps fill in the knowledge gaps existing on the lignocellulosic biomass application for xylitol bioproduction and biorefinery industries.

Made available in DSpace on 2014-06-11T19:31:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-07-31Bitstream added on 2014-06-13T20:01:21Z : No. of bitstreams: 1 tavano_ol_dr_araiq.pdf: 761592 bytes, checksum: 1c98a6250ff1a76b1380af40256bd7b4 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho estudou-se a possibilidade de imobilização de uma amilase produzida por cepa de Neurospora crassa (mutante exo-1), e produção de derivados ativos e estabilizados. Foram testados diferentes suportes sólidos, incluindo-se diferentes suportes de agarose e suportes epóxidos preparados com Eupergit e Sepabeads. Além da agarose 10BCL foi utilizada a agarose 4BCL para que se verificasse possíveis dificuldades difusionais do substrato desta enzima, o amido. O acompanhamento das cinéticas de imobilização com a maltose como alternativa ao amido, também colaborou em evidenciar a dificuldade de difusão do amido através de ambos os suportes glioxil-agarose. O derivado obtido com agarose 10BCL, assim como aquele produzido com uso de suporte Eupergit foram os derivados mais estáveis, capazes de manter 100% de suas atividades após 12 horas de incubação à temperatura de 60°C, quando na forma solúvel a enzima conservou apenas 12% de sua atividade inicial. Quando incubados a 70°C destacou-se o derivado de glioxil-agarose (10BCL) como mais estável, mantendo cerca de 30% de sua atividade inicial após 4 horas de incubação. Quando testada a utilização de uma agarose comercial alternativa, sem percentual de crosslink conhecido, de menor custo, sua aplicação mostrou-se promissora e os derivados produzidos além de ativos se apresentam estáveis frente à temperatura. Em conjunto, as informações contidas no presente estudo indicam que a amilase de Neurospora crassa apresenta-se promissora em comparação às amilases de mercado aqui estudadas, tanto em sua utilização na forma solúvel quanto no que se relaciona a produção de derivados estáveis. / In this work were studied the immobilization of amylase from Neurospora crassa (Mutant Exo-1). This amylase showed easily production, purification and high capacity of immobilization on agarose and epoxy supports. It was used crosslinked agarose with two polymer concentration: 4 and 10%. The 4BCL agarose presents bigger porous diameter than 10 BCL agarose, so, in this case, possible diffusion problems of the starch across the supports could be reduced. Also, in this study, we have tested two epoxy supports for this amylase immobilization, using Eupergit and Sephabeads supports. The activies of the obtained derivatives were measured using two substrates - maltose and starch. Both glyoxyl agarose support prepared with 4BCl and 10BCL agarose present diffusion problems when the starch was used as substrate to measure the immobilization course. The 10BCL glyoxyl derivative presented the highest thermal stability when comparing the others derivatives. Among the epoxy derivatives the Eupergit one were better than the derivatives obtained using Sepabeads as support. In a confrontation between the two best derivatives, that is, the glyoxyl 10 BCL and Eupergit derivatives, both of them were stable at 60º incubation, maintaining 100% of activities for 12 hours, while the soluble amylase preserved about 12% of initial activity. These two amylase derivatives only showed differences at 70ºC incubation, when the glyoxyl 10BCL amylase derivative was more thermally stable, preserving about 30% of the initial activity after 4 hours.

Coumaphos is an organophosphate insecticide used predominantly by the US Department of Agriculture, Animal and Plant Health Inspection Services for its tick eradication program. Bioremediation of the hydrolysis products of coumaphos, chlorferon and diethylthiophosphate (DETP), using Ca-alginate immobilized cells was the focus of this research. Consortia of indigenous microorganisms capable of degrading chlorferon and DETP were isolated separately. Since chlorferon inhibited both chlorferon-degrading and DETP-degrading organisms, it was not possible to enrich a consortium of organisms for simultaneous degradation of chlorferon and DETP. A two-step growth procedure was developed for degradation studies to provide biomass acclimated to the target compound and reaction medium since cells lost their degradation activity during the growth in a rich medium. Without acclimation, approximately a week-long lag period was required before degradation was initiated. Optimum reaction conditions were found for the degradation of chlorferon and DETP using free cells. Reaction kinetics of chlorferon and DETP were determined using enzyme kinetics because cell growth was not observed during the degradation. Chlorferon degradation followed substrate inhibition kinetics and DETP degradation followed simple Michaelis-Menten kinetics. A calcium-alginate immobilized cell system was developed, and the optimum bead loadings in the reactor were determined. Degradation rates for immobilized cells were enhanced up to five times that for free cells in untreated cattle dip (UCD) solution. The enhanced degradation of immobilized cells was due to protection of the cells from inhibitory substances present in the UCD solution. In addition, physiological changes of cells caused by Ca-alginate immobilization may have contributed to a slightly increased reaction rate in pure solution. Diffusion coefficients of chlorferon and DETP into Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients of chlorferon and DETP increased with increasing agitation speed and decreasing substrate concentration. Increased cell concentration in gel beads caused lower diffusivity. Calcium-alginate gel beads used in this study were not subject to diffusional limitations. Both external and internal mass transfer resistances were negligible, and the degradation rate inside Ca-alginate gel beads was reaction-limited.

Coumaphos is an organophosphate insecticide used predominantly by the US Department of Agriculture, Animal and Plant Health Inspection Services for its tick eradication program. Bioremediation of the hydrolysis products of coumaphos, chlorferon and diethylthiophosphate (DETP), using Ca-alginate immobilized cells was the focus of this research. Consortia of indigenous microorganisms capable of degrading chlorferon and DETP were isolated separately. Since chlorferon inhibited both chlorferon-degrading and DETP-degrading organisms, it was not possible to enrich a consortium of organisms for simultaneous degradation of chlorferon and DETP. A two-step growth procedure was developed for degradation studies to provide biomass acclimated to the target compound and reaction medium since cells lost their degradation activity during the growth in a rich medium. Without acclimation, approximately a week-long lag period was required before degradation was initiated. Optimum reaction conditions were found for the degradation of chlorferon and DETP using free cells. Reaction kinetics of chlorferon and DETP were determined using enzyme kinetics because cell growth was not observed during the degradation. Chlorferon degradation followed substrate inhibition kinetics and DETP degradation followed simple Michaelis-Menten kinetics. A calcium-alginate immobilized cell system was developed, and the optimum bead loadings in the reactor were determined. Degradation rates for immobilized cells were enhanced up to five times that for free cells in untreated cattle dip (UCD) solution. The enhanced degradation of immobilized cells was due to protection of the cells from inhibitory substances present in the UCD solution. In addition, physiological changes of cells caused by Ca-alginate immobilization may have contributed to a slightly increased reaction rate in pure solution. Diffusion coefficients of chlorferon and DETP into Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients of chlorferon and DETP increased with increasing agitation speed and decreasing substrate concentration. Increased cell concentration in gel beads caused lower diffusivity. Calcium-alginate gel beads used in this study were not subject to diffusional limitations. Both external and internal mass transfer resistances were negligible, and the degradation rate inside Ca-alginate gel beads was reaction-limited.

Three-dimensional biomolecule patterned hydrogels provide cellular microenvironments that mimic in vivo conditions. We are particularly interested in the fabrication of materials to spatially control stem cell differentiation towards the creation of tissue analogues. To this end, we have designed a 3D protein patterning system where differentiation factors were immobilized within distinct volumes through two-photon chemistry, which provides 3D control since the excitation volume is limited to the focal point of the laser. Agarose hydrogels were modified with 6-bromo-7-hydroxy-coumarin (Bhc) protected amines or thiols, which upon two-photon excitation are deprotected in defined volumes yielding reactive amines or thiols. Fibroblast growth factor-2 (FGF-2) was immobilized onto agarose-thiol-Bhc through either disulfide bond formation with agarose thiols or the physical interaction between human serum albumin (HSA) and the albumin binding domain (ABD). The use of biological binding pairs also provides mild immobilization conditions, minimizing the risk for bioactivity loss. Similarly, two differentiation factors for retinal stem progenitor cells were simultaneously immobilized: 1) ciliary neurotrophic factor (CNTF); and 2) N-terminal sonic hedgehog (SHH). Maleimide modified binding proteins, such as maleimide-streptavidin; react with exposed thiols, yielding 3D patterns of covalently immobilized streptavidin in agarose hydrogels. Growth factors are then introduced as fusion proteins with binding domains, such as biotin-CNTF, for complexation and thus 3D immobilization. By combining multiple binding systems with two-photon patterning, we were able to simultaneously 3D immobilize proteins towards the creation biomimetic hydrogels.

Three-dimensional biomolecule patterned hydrogels provide cellular microenvironments that mimic in vivo conditions. We are particularly interested in the fabrication of materials to spatially control stem cell differentiation towards the creation of tissue analogues. To this end, we have designed a 3D protein patterning system where differentiation factors were immobilized within distinct volumes through two-photon chemistry, which provides 3D control since the excitation volume is limited to the focal point of the laser. Agarose hydrogels were modified with 6-bromo-7-hydroxy-coumarin (Bhc) protected amines or thiols, which upon two-photon excitation are deprotected in defined volumes yielding reactive amines or thiols. Fibroblast growth factor-2 (FGF-2) was immobilized onto agarose-thiol-Bhc through either disulfide bond formation with agarose thiols or the physical interaction between human serum albumin (HSA) and the albumin binding domain (ABD). The use of biological binding pairs also provides mild immobilization conditions, minimizing the risk for bioactivity loss. Similarly, two differentiation factors for retinal stem progenitor cells were simultaneously immobilized: 1) ciliary neurotrophic factor (CNTF); and 2) N-terminal sonic hedgehog (SHH). Maleimide modified binding proteins, such as maleimide-streptavidin; react with exposed thiols, yielding 3D patterns of covalently immobilized streptavidin in agarose hydrogels. Growth factors are then introduced as fusion proteins with binding domains, such as biotin-CNTF, for complexation and thus 3D immobilization. By combining multiple binding systems with two-photon patterning, we were able to simultaneously 3D immobilize proteins towards the creation biomimetic hydrogels.

A biosensor is proposed that contains bacteria that naturally effluxes potassium ions when threatened by electrophilic species. Pseudomonas aeruginosa is an activated sludge isolate and possesses the characteristic potassium efflux response. It has been immobilized in calcium alginate beads, photopolymer disks, and a thermally reversible gel in order to ultimately incorporate the immobilized system into a functional biosensor. The potassium efflux and cell viability were measured in the immobilized matrices. Wastewater treatment is of utmost importance; however, processes are easily upset. Upsets can be caused by various electrophiles found in the environment, and can cause serious health effects to people or the environment downstream from an upset. Electrophiles can cause the activated sludge in wastewater treatment facilities to deflocculate, and untreated water can be lost downstream. Devising a detection system for proactively sensing electrophiles prior to an upset is an important complementary goal. Immobilization systems have been evaluated including photopolymer coated alginate beads and sol gel coated alginate beads. The thermally reversible gel, NIPA-co-AAc (N-isopropylacrylamide-co-acrylic acid), shows promise as an immobilization matrix for the bacteria; however its high lower critical solution temperature (LCST) of ~33oC is problematic for typical, ambient applications. Another thermally reversible copolymer, N-isopropylacrylamide-co-N-acryloyl-6-amino caproic acid (NIPA-co-AcACA) was synthesized; however, it did not form a continuous matrix; making it useless as an immobilization scheme for biosensors. Alginate beads fall apart easily in bacteria media, but are structurally stable in potassium solutions. Cells immobilized in alginate beads seemed to efflux four times less potassium than did planktonic controls, while cells in thermally reversible gels effluxed a comparable amount of potassium as planktonic controls. This result may indicate a tighter matrix around the alginate immobilized cells, not allowing proper diffusion of potassium out of the matrix. / Master of Science

Biofunctional interfaces capable of anchoring biomolecules and nanoparticles of interest onto a platform are the key components of many biomedical assays, clinical pathologies, as well as antibacterial and antiviral surfaces. In an ideal biofunctional surface, bio-entities and particles are covalently immobilized on a substrate in order to provide robustness and long-term stability. Nonetheless, most of the reported covalent immobilization strategies incorporate complex wet-chemical steps and long incubation times hindering their implementation for mass production and commercialization. Another essential factor in the biointerface preparation, specially with regard to biosensors and diagnostic applications, is utilization of an efficient and durable blocking agent that can inhibit non-specific adsorption of biomolecules thereby enhancing the sensitivity of sensors by diminishing the level of background noise. Many of the commonly used blocking agents lack proper prevention of non-specific adsorption in complex fluids. In addition, most of these agents are physically attached to surfaces making them unreliable for long-term usage in harsh environments (i.e. where shear stresses above 50 dyn/cm2 or strong washing buffers are involved). This thesis presents novel and versatile strategies to covalently immobilize nanoparticles and biomolecules on substrates. The new surface coating techniques are first implemented for robust attachment of TiO2 nanoparticles onto ceramic tiles providing self-cleaning properties. Further, we utilize similar strategies to covalently immobilize proteins and culture cells in microfluidic channels either as a full surface coating or as micropatterns of interest. The new strategies allow us to obtain adhesion of ~ 400 cells/mm2 in microfluidic channels after only 1-day incubation, which is not achievable by the conventional methods. Moreover, we show the possibility of covalently micropatterning of biomolecules on lubricant-infused surfaces (LISs) so as to attain a new class of biofunctional LISs. By integration of these surfaces into a biosensing platform, we are able to detect interleukin 6 (IL-6) in a complex biofluid of human whole plasma with a limit of detection (LOD) of 0.5 pg.mL-1. This LOD is significantly lower than the smallest reported IL-6 LOD in plasma, 23 pg mL-1, using a complex electrochemical system. The higher sensitivity of our developed biosensor can be attributed to the distinguish capability of biofunctional LISs in preventing non-specific adhesion of biomolecules compared to other blocking agents. / Thesis / Doctor of Philosophy (PhD) / The key goal of this thesis is to provide new strategies for preparation of robust and durable biointerfaces that could be employed for many biomedical devices such as self-cleaning coatings, microfluidics, point-of-care diagnostics, biomedical assays, and biosensors in order to enhance their efficiency, sensitivity, and precision. The introduced surface biofunctionalization methods are straightforward to use and do not require multiple wet-chemistry steps and incubation times, making them suitable for mass production and high throughput demands. Moreover, the introduced surface coating strategies allow for creation of antibody/protein micro-patterns covalently bound onto a biomolecule-repellent surface. The repellent property of the surfaces is resulted from infusion of an FDA-approved lubricant into the surface of a chemically modified substrate. While the surface repellency can effectively prevent non-specific adhesion of biomolecules, the patterned antibodies can locally capture the desired analyte, making them a great candidate for biosensing.