Bacterial Cellulose Microfibrils Research Articles

Molecular Cloning, In Silico Analysis, and Characterization of a Novel Cellulose Microfibril Swelling Gene Isolated from Bacillus sp. Strain AY8.

A novel cellulose microfibril swelling (Cms) gene of Bacillus sp. AY8 was successfully cloned and sequenced using a set of primers designed based on the conserved region of the gene from the genomic database. The molecular cloning of the Cms gene revealed that the gene consisted of 679 bp sequences encoding 225 amino acids. Further in silico analysis unveiled that the Cms gene contained the NlpC/P60 conserved region that exhibited a homology of 98% with the NlpC/P60 family proteins found in both the strains, Burkholderialata sp. and Burkholderia vietnamiensis. The recombinant Cms enzyme had a significant impact on the reduction of crystallinity indices (CrI) of various substrates including a 3%, a 3.97%, a 4.66%, and a substantial 14.07% for filter paper, defatted cotton fiber, avicel, and alpha cellulose, respectively. Additionally, notable changes in the spectral features were observed among the substrates treated with recombinant Cms enzymes compared to the untreated control. Specifically, there was a decrease in band intensities within the spectral regions of 3000-3450 cm-1, 2900 cm-1, 1429 cm-1, and 1371 cm-1 for the treated filter paper, cotton fiber, avicel, and alpha cellulose, respectively. Furthermore, the recombinant Cms enzyme exhibited a maximum cellulose swelling activity at a pH of 7.0 along with a temperature of 40 °C. The molecular docking data revealed that ligand molecules, such as cellobiose, dextrin, maltose 1-phosphate, and feruloyated xyloglucan, effectively bonded to the active site of the Cms enzyme. The molecular dynamics simulations of the Cms enzyme displayed stable interactions with cellobiose and dextrin molecules up to 100 ns. It is noteworthy to mention that the conserved region of the Cms enzyme did not match with those of the bioadditives like expansins and swollenin proteins. This study is the initial report of a bacterial cellulose microfibril swellase enzyme, which could potentially serve as an additive to enhance biofuel production by releasing fermentable sugars from cellulose.

Effect of in-situ biochemical modification on the synthesis, structure, and function of xanthan gum based bacterial cellulose generated from Tieguanyin oolong tea residue hydrolysate

The effect of in-situ biochemical modification on the synthesis, structure, and function of xanthan gum based bacterial cellulose generated from Tieguanyin oolong tea residue hydrolysate was evaluated for the first time. This modification could overcome the inhibitory effect of the hydrolysate and the bacterial cellulose yield with 0.6% xanthan gum addition increased by 260.8% compared with that without xanthan gum addition. Bacterial cellulose and xanthan gum were combined by the in-situ modification and the alteration of fermentation medium rheological properties by xanthan gum addition might be beneficial for their combination. The average diameter of the bacterial cellulose microfibrils was increased by the modification, and it had a great influence on the crystalline structure of the bacterial cellulose. Additionally, both the water absorption and texture properties of the bacterial cellulose was strengthened by the modification. Overall, this modification showed great potential for efficient and effective xanthan gum based bacterial cellulose production.

Adjuvant action of needle-shaped BC microfibrils.

Bacterial cellulose (BC) is an unbranched biopolymer produced by microorganisms and composed of glucopyranose units linked by β-1,4 bonds. This study investigates the adjuvant action of needle-shaped BC microfibrils (BCmFs) in vitro using bovine serum albumin (BSA) as a model antigen. BC produced by the static culture of Komagataibacter xylinus was then microparticled (1-5μm) by acid hydrolysis and characterized using Dynamic Light Scattering and Scanning Electron Microscopy. Subsequently, Attenuated Total Reflectance-Fourier-Transform Infrared Spectroscopy, cytotoxicity, TNF-α (tumour necrosis factor-alpha) and IL-6 (interleukin-6) cytokine secretion, and cellular uptake of the BCmFs-BSA conjugate on the human monocyte cell line (U937) differentiated into macrophages were performed. The microfibrils were determined to be 1-5μm in size, needle-shaped, with a zeta potential of - 32mV. Their conjugation with the model antigen, BSA, was demonstrated by FTIR analysis. In the cytotoxicity assay, BCmFs-BSA in macrophage cells showed high viability (over 70%). Although the highest TNF-α cytokine level (113pg/ml) was obtained with BCmFs-BSA (Bovine serum albumin) conjugate (500µg/ml) and was statistically significant (p = 0.0001) compared to the positive control group (BSA-aluminium hydroxide), IL-6 cytokine levels were not statistically different from those in the control group as desired. It has been shown in macrophage-differentiated U937 cells that microbially synthesized BC in the form of needle-shaped microfibrils (BCmFs) has a high cellular uptake capacity and increases the immunogenicity of the antigen. These results demonstrate for the first time that BCmFs have the potential to serve as a vaccine adjuvant.

Unraveling the Supramolecular Structure and Nanoscale Dislocations of Bacterial Cellulose Ribbons Using Correlative Super-Resolution Light and Electron Microscopy.

Cellulose is a structural linear polysaccharide that is naturally produced by plants and bacteria, making it the most abundant biopolymer on Earth. The hierarchical structure of cellulose from the nano- to microscale is intimately linked to its biosynthesis and the ability to process this sustainable resource for materials applications. Despite this, the morphology of bacterial cellulose microfibrils and their assembly into higher order structures, as well as the structural origins of the alternating crystalline and disordered supramolecular structure of cellulose, have remained elusive. In this work, we employed high-resolution transmission electron and atomic force microscopies to study the morphology of bacterial cellulose ribbons at different levels of its structural hierarchy and provide direct visualization of nanometer-wide microfibrils. The non-persistent twisting of cellulose ribbons was characterized in detail, and we found that twists are associated with nanostructural defects at the bundle and microfibril levels. To investigate the structural origins of the persistent disordered regions that are present along cellulose ribbons, we employed a correlative super-resolution light and electron microscopy workflow and observed that the disordered regions that can be seen in super-resolution fluorescence microscopy largely correlated with the ribbon twisting observed in electron microscopy. Unraveling the hierarchical assembly of bacterial cellulose and the ultrastructural basis of its disordered regions provides insights into its biosynthesis and susceptibility to hydrolysis. These findings are important to understand the cell-directed assembly of cellulose, develop new cellulose-based nanomaterials, and develop more efficient biomass conversion strategies.

Tribological and electrical properties of C/C composites with bacterial cellulose

Bacterial cellulose (BC) synthesized by Acetobacter xylinum is one of the nano fiber materials. In this paper, the aggregation and dispersion behavior of C/C composite made with the BC and copper powders as a third constituent were considered. It is found that BC microfibril network can set copper powders into fine dispersion in the mBC-C/C composite. The tribological and electrical properties of Cu/mBC-C/C composite containing copper powder were also evaluated. From the experimental results, the mean value of the specific wear amount was at 10-9 order, the dynamic friction coefficient was about 0.2 and the electrical resistivity was at 10-4 order. Furthermore, the wear properties got worse due to the large amount of copper powder and the improvement in electrical conductivity was not enough. It is considered that it is necessary to find the optimum content of copper powder for the improvement of electrical conductivity in order to use for the conduction/friction material, for instance, brush for the DC motor.

Bacterial Cellulose Synthesis by Gluconacetobacter xylinus: Enhancement via Fed-batch Fermentation Strategies in Glycerol Media

Bacterial cellulose (BC) is an abundant polysaccharide, which is secreted by several genera of bacteria. It has remarkable characteristics, which include high purity, high tensile strength, high biocompatibility and non-toxic. The main feature that differentiates BC and plant cellulose (PC) is the absence of contaminants such as lignin, hemicellulose and pectin. However, the main drawbacks in producing BC are low yield and expensive carbon source. Due to that, this study was carried out to enhance BC volumetric productivity in fed-batch operation mode using glycerol as a carbon source. BC was produced in fill-and-draw and pulse-feed fed-batch cultures of Gluconacetobacter xylinus DSM 46604 in a 3-L bench-top bioreactor. The fed-batch fermentation trials were conducted in agitated and aerobic conditions at 30 ºC. For fill-and-draw fed-batch culture, a total of 24.2 g/L of BC accumulated in the bioreactor after 9 days, which corresponded to a yield and productivity of 0.2 g/g and 2.69 g/L/day, respectively. Pulse-feed fed-batch fermentation resulted in a yield and volumetric productivity of 0.38 g/g and 2.71 g/L/day, respectively. The pulse-feed fed-batch culture proved to be a better fermentation system for utilizing glycerol, which is a low-cost and abundant carbon source.
 HIGHLIGHTS
 
 Komagataeibacter species, which were formerly known as Acetobacter or Gluconacetobacter is one of the Gram-negative BC producers that secretes a large quantity of BC microfibrils extracellularly
 One of the main challenges in bacterial cellulose (BC) production is low productivity and high processing cost
 As fed-batch fermentation is one of the operation modes in bioprocess that can control the microbial growth rate, this operation mode is conducted to enhance the yield of BC, substrate consumption and also volumetric productivity
 Fill-and-draw and pulse feed fed-batch culture were conducted to enhance yield and volumetric productivity. The pulse-feed fed-batch culture resulted to be a favorable operation mode for utilizing glycerol, which is a low-cost and abundant carbon source
 
 GRAPHICAL ABSTRACT

Shear-induced unidirectional deposition of bacterial cellulose microfibrils using rising bubble stream cultivation

In crystalline cellulose I, all glucan chains are ordered from reducing ends to non-reducing ends. Thus, the polarity of individual chains is added forming a large dipole within the crystal. If one can engineer unidirectional alignment (parallel packing) of cellulose crystals, then it might be possible to utilize the material properties originating from polar crystalline structures. However, most post-synthesis manipulation methods reported so far can only achieve the uniaxial alignment with bi-directionality (antiparallel packing). Here, we report a method to induce the parallel packing of bacterial cellulose microfibrils by applying unidirectional shear stress during the synthesis and deposition through the rising bubble stream in a culture medium. Driving force for the alignment is explained with mathematical estimation of the shear stress. Evidences of the parallel alignment of crystalline cellulose Iα domains were obtained using nonlinear optical spectroscopy techniques.

Composite Gels Containing Whey Protein Fibrils and Bacterial Cellulose Microfibrils.

In this study, we investigated the gelation of WPI fibrils in the presence of bacterial cellulose (BC) microfibrils at pH 2 upon prolonged heating. Rheology and microstructure were investigated as a function of BC microfibril concentration. The presence of BC microfibrils did not influence the gelation dynamics and resulting overall structure of the WPI fibrillar gel. The storage modulus and loss modulus of the mixed WPI‐BC microfibril gels increased with increasing BC microfibril concentration, whereas the ratio between loss modulus and storage modulus remained constant. The WPI fibrils and BC microfibrils independently form two coexisting gel networks. Interestingly, near to the BC microfibrils more aligned WPI fibrils seemed to be formed, with individual WPI fibrils clearly distinguishable. The level of alignment of the WPI fibrils seemed to be dependent on the distance between BC microfibrils and WPI fibrils. This also is in line with our observation that with more BC microfibrils present, WPI fibrils are more aligned than in a WPI fibrillar gel without BC microfibrils. The large deformation response of the gels at different BC microfibril concentration and NaCl concentration is mainly influenced by the concentration of NaCl, which affects the WPI fibrillar gel structures, changing form linear fibrillar to a particulate gel. The WPI fibrillar gel yields the dominant contribution to the gel strength.

Mixed gels from whey protein isolate and cellulose microfibrils

Whey proteins can form different gel structures ranging from fine-stranded to particulate when appropriate conditions are applied. By incorporating polysaccharides, the gelation of WPI can be influenced. We investigated the heat-induced gelation of whey protein isolate (WPI) in the presence of bacterial cellulose (BC) microfibrils at pH 7 at different concentrations of NaCl. Our results showed that WPI and BC microfibrils form a homogeneous dispersion at pH 7. Upon heating, the WPI gel was formed independently in the presence of the BC microfibril gel, resulting in the formation of a composite gel. The gel structure and gelation dynamics of WPI was not influenced by the presence of BC microfibrils. However, the presence of BC microfibrils increased the storage modulus of the WPI gel, with an increase being negligible when the strength of the WPI gel is above a certain value. With an increase of NaCl concentration, the WPI gel structure changes from fine-stranded to a particulate gel, while the BC microfibril gel structure remains unchanged. No macroscopic phase separation could be observed in the WPI-BC microfibril gels. Our results showed that the rheological properties and water holding capacity of the WPI-BC microfibril mixed gels are mainly dominated by the WPI.

Insights into Bacterial Cellulose Biosynthesis from Different Carbon Sources and the Associated Biochemical Transformation Pathways in Komagataeibacter sp. W1.

Cellulose is the most abundant and widely used biopolymer on earth and can be produced by both plants and micro-organisms. Among bacterial cellulose (BC)-producing bacteria, the strains in genus Komagataeibacter have attracted wide attention due to their particular ability in furthering BC production. Our previous study reported a new strain of genus Komagataeibacter from a vinegar factory. To evaluate its capacity for BC production from different carbon sources, the present study subjected the strain to media spiked with 2% acetate, ethanol, fructose, glucose, lactose, mannitol or sucrose. Then the BC productivity, BC characteristics and biochemical transformation pathways of various carbon sources were fully investigated. After 14 days of incubation, strain W1 produced 0.040–1.529 g L−1 BC, the highest yield being observed in fructose. Unlike BC yields, the morphology and microfibrils of BCs from different carbon sources were similar, with an average diameter of 35–50 nm. X-ray diffraction analysis showed that all membranes produced from various carbon sources had 1–3 typical diffraction peaks, and the highest crystallinity (i.e., 90%) was found for BC produced from mannitol. Similarly, several typical spectra bands obtained by Fourier transform infrared spectroscopy were similar for the BCs produced from different carbon sources, as was the Iα fraction. The genome annotation and Kyoto Encyclopedia of Genes and Genomes analysis revealed that the biochemical transformation pathways associated with the utilization of and BC production from fructose, glucose, glycerol, and mannitol were found in strain W1, but this was not the case for other carbon sources. Our data provides suggestions for further investigations of strain W1 to produce BC by using low molecular weight sugars and gives clues to understand how this strain produces BC based on metabolic pathway analysis.

Characteristics of Curcumin-Loaded Bacterial Cellulose Films and Anticancer Properties against Malignant Melanoma Skin Cancer Cells

Curcumin-loaded bacterial cellulose films were developed in this study. Curcumin was absorbed into never-dried bacterial cellulose pellicles by 24-h immersion in solutions of curcumin in the range of 0.2–1.0 mg /mL. The curcumin-loaded bacterial cellulose pellicles were then air-dried and characterized. The mechanical properties of curcumin-loaded bacterial cellulose films, particularly the stretching properties, appeared to be lower than those of bacterial cellulose film. This was especially evident when the loading concentration of curcumin was higher than 0.4 mg/mL. Fourier-transform infrared spectroscopy analysis indicated an interaction between bacterial cellulose microfibrils and curcumin. Controlled release of curcumin was achieved in buffer solutions containing Tween 80 and methanol additives, at pH 5.5 and 7.4. Curcumin-loaded bacterial cellulose films prepared with curcumin solutions at concentrations of 0.5 and 1.0 mg/mL displayed antifungal activities against Aspergillus niger. They also exhibited anticancer activity against A375 malignant melanoma cells. No significant cytotoxic effect was observed against normal dermal cells, specifically, human keratinocytes and human dermal fibroblasts.

Bacterial Cellulose Ionogels as Chemosensory Supports.

To fully leverage the advantages of ionic liquids for many applications, it is necessary to immobilize or encapsulate the fluids within an inert, robust, quasi-solid-state format that does not disrupt their many desirable, inherent features. The formation of ionogels represents a promising approach; however, many earlier approaches suffer from solvent/matrix incompatibility, optical opacity, embrittlement, matrix-limited thermal stability, and/or inadequate ionic liquid loading. We offer a solution to these limitations by demonstrating a straightforward and effective strategy toward flexible and durable ionogels comprising bacterial cellulose supports hosting in excess of 99% ionic liquid by total weight. Termed bacterial cellulose ionogels (BCIGs), these gels are prepared using a facile solvent-exchange process equally amenable to water-miscible and water-immiscible ionic liquids. A suite of characterization tools were used to study the preliminary (thermo)physical and structural properties of BCIGs, including no-deuterium nuclear magnetic resonance, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. Our analyses reveal that the weblike structure and high crystallinity of the host bacterial cellulose microfibrils are retained within the BCIG. Notably, not only can BCIGs be tailored in terms of shape, thickness, and choice of ionic liquid, they can also be designed to host virtually any desired active, functional species, including fluorescent probes, nanoparticles (e.g., quantum dots, carbon nanotubes), and gas-capture reagents. In this paper, we also present results for fluorescent designer BCIG chemosensor films responsive to ammonia or hydrogen sulfide vapors on the basis of incorporating selective fluorogenic probes within the ionogels. Additionally, a thermometric BCIG hosting the excimer-forming fluorophore 1,3-bis(1-pyrenyl)propane was devised which exhibited a ratiometric (two-color) fluorescence output that responded precisely to changes in local temperature. The ionogel approach introduced here is simple and has broad generality, offering intriguing potential in (bio)analytical sensing, catalysis, membrane separations, electrochemistry, energy storage devices, and flexible electronics and displays.

Effect of cellulose crystallinity on bacterial cellulose assembly

Bacterial cellulose (BC) is a promising biomaterial as well as a model system useful for investigating cellulose biosynthesis. BC produced under static cultivation condition is a hydrous pellicle consisting of an interconnected network of fibrils assembled in numerous dense layers. The mechanisms responsible for this layered BC assembly remain unknown. This study used calcofluor as a fluorescent marker to examine BC layer formation at the air/liquid interface. Layers are found to move downward into the media after formation while new layers continue to form at the air/liquid interface. Calcoflour is also known to reduce the crystallinity of cellulose, changing the mechanical properties of the formed BC microfibrils. Consecutive addition and accumulation of calcofluor in the culture medium is found to disrupt the layered assembly of BC. BC crystalllinity decreased by 22 % in the presence of 12 % calcofluor (v/v) in the medium as compared to BC produced without calcofluor. This result suggests that cellulose crystallinity and the mechanical properties which crystallinity provides to cellulose are major factors influencing the layered BC structure formed during biosynthesis.

Fourier-transform infrared spectroscopic analyses of cellulose from different bacterial cultivations using microspectroscopy and a high-throughput screening device

Broad application of bacterial cellulose (BC) has led to search for new commercially interesting producers and consequently also for low-cost screening methods to select BC with particular properties. BC produced by four symbiotic Kombucha associations and fourteen acetic acid bacteria isolated from these Kombucha associations were purified by frequent washing with distilled water and pre-treatment with alkali. The obtained native and mercerized BC pellicles were analysed by two common time-saving FT-IR spectroscopy methods—high-throughput screening (HTS) and microspectroscopy. The FT-IR spectra showed traces of microbial cells and acids entrapped between the microfibrils of BC even after purification with alkali. This study showed that spectra of BC collected with HTS are more informative for the evaluation of the purity of BC than those obtained by microspectroscopy, which will be preferable for studies of crystallinity. Hierarchical cluster analysis of IR-spectra was helpful for fast screening of BC samples by their producer, fermentation medium, purity, and crystallinity. This study demonstrated HTS and IR-microspectroscopy as quick and cost-efficient methods for screening of BC and search of BC with particular properties.

Controllable Micro/nano Biofabrication of Fascinating Composites based on Bacterial Cellulose

Event Abstract Back to Event Controllable Micro/nano Biofabrication of Fascinating Composites based on Bacterial Cellulose Guang Yang1 1 Huazhong University of Science & Technology, Department of Biomedical Engineering, College of Life Science & Technology, China Microorganisms in nature have rich variety, whose sizes are from nano to microscale. Therefore, microbes can be used as natural building blocks in nano/micro multilevel fabrication processes. Based on the urgent need of micro/nano biological manufacture of microorganism, four controlling methods: molecular template, magnetic control, microfluidics, and bio-printing for biological manufacture process suitable for microbe have been proposed to dip into the moving mode of microorganism and design new micro/nano functional materials by controlling directed movement and ordered arrangement of microorganism living cells. It could be really creative attempts in the microbial field. Bacterial cellulose (BC) is secreted by microorganism. Its biocompatibility, mechanical strength, chemical and morphologic controllability make it a natural choice for adoption in biomedical fields, including use as biomaterial for wound dressing, artificial blood vessels, vascular grafts, scaffolds for tissue engineering and controlled-release drug carriers. More than that, BC is a natural hydrogel, its high water content can carry other monomeric, reactive and potentially polymerizable species into BC’s inner network, essentially occupying the void volume and interacting with chain segments or pendant moieties of the BC. Therefore, Varity of composites based BC were synthesized and expand the application of BC. BC composites are primarily synthesized through in situ addition of reinforcement materials to BC synthetic media or the ex situ penetration of such materials into BC microfibrils. In our group’s research, Micropatterned BC can be guided neuronal growth, tubular BC can be used as artificial blood vessel. BC combine with biomacromolecules such as chitosan, hyaluronic acid, Au-DAPT nanoparticles, collagen, silk fibroin and so on, can be used in wound dressing and cosmetic. BC combine with Poly(NIPAM-co-BMA), which has thermoresponsive property, suitable for vascular embolization interventional therapy. BC combine with carbon nanotubes or conductive polymers, which has electractive property, can be used as flexible supercapacitor, electrodes, and have potential to be used to build a biology–device interface to produce implantable biosensors, electrostimulated drug release devices, and implantable devices for personalized and regenerative medicine. This work was supported by the National Natural Science Foundation of PR China (21574050, 31270150)

Production and characterization of bacterial cellulose by Leifsonia sp. CBNU-EW3 isolated from the earthworm, Eisenia fetida

A total of five bacterial strains were isolated from earthworm, Eisenia fetida and examined for bacterial cellulose (BC) production in Hestrin-Schramm medium (HS). Among the five strains tested, CBNU-EW3 exhibited excellent BC production and was identified as Leifsonia sp. by 16S rDNA sequence analysis. BC production by Leifsonia sp. CBNU-EW3 was optimum at pH 5, 30°C, and with glucose and yeast extract as carbon and nitrogen sources, respectively, according to 15 day-long experiments. (XRD) analysis of the dried pellicle indicated that the BC was partially crystalline type I. Fourier transform infrared spectroscopy (FT-IR) analysis showed that the obtained pellicle contained the same functional groups as typical BC. Field emission scanning electron microscopy (FESEM) images showed that the BC micro-fibril matrix consisted of a flat surface with large pore size and cellulose aggregation.

The effect of fibril length and architecture on the accessibility of reducing ends of cellulose Iα to Trichoderma reesei Cel7A

The origin of the recalcitrance of cellulose fibrils to enzymatic hydrolysis is still poorly understood. In this study we examined the role of cellulose fibril lengths and fibril architecture, i.e. the fibrillar structure from lateral association of cellulose microfibrils, on the accessibility to a reducing-end specific cellobiohydrolase, Trichoderma reesei Cel7A (TrCel7A). Cellulose Iα fibrils from Gluconacetobacter xylinus and Cladophora aegagropila showed contrasting digestibility by TrCel7A. Where the bacterial cellulose (BC) fibrils from G. xylinus were rapidly hydrolyzed to near completion by TrCel7A (>99 %) in 120 h, under identical reaction conditions, TrCel7A hydrolysis of the algal cellulose (AC) fibrils from C. aegagropila was slow and limited (~30 %). Mechanically decreasing fibril lengths and increasing average reducing end concentrations by high intensity ultrasonication did not affect the hydrolysis rates of either BC or AC by TrCel7A. Moreover, ultrasonicated AC remained significantly less digestible by TrCel7A than BC despite higher available reducing-end concentrations. In contrast to previous observations of extensive fibrillation of BC by TrCel7A hydrolysis, AC fibrils subjected to hydrolysis by TrCel7A remained associated. The hydrolysis of AC fibrils by TrCel7A roughened the topography of the fibril surfaces in a manner suggesting erosion of microfibrils at the fibril surface. We speculate that the compact cross-sections of the AC microfibrils result in tightly associated fibrils that hinder enzyme access to available reducing ends while the flat, ribbon cross section of the BC microfibrils result in more loosely associated fibrils that more easily dissociate during hydrolysis to improve accessibility and overall digestibility by TrCel7A.

Multi-mode binding of Cellobiohydrolase Cel7A from Trichoderma reesei to cellulose.

Enzymatic hydrolysis of recalcitrant polysaccharides like cellulose takes place on the solid-liquid interface. Therefore the adsorption of enzymes to the solid surface is a pre-requisite for catalysis. Here we used enzymatic activity measurements with fluorescent model-substrate 4-methyl-umbelliferyl-β-D-lactoside for sensitive monitoring of the binding of cellobiohydrolase TrCel7A from Trichoderma reesei to bacterial cellulose (BC). The binding at low nanomolar free TrCel7A concentrations was exclusively active site mediated and was consistent with Langmuir's one binding site model with K d and A max values of 2.9 nM and 126 nmol/g BC, respectively. This is the strongest binding observed with non-complexed cellulases and apparently represents the productive binding of TrCel7A to cellulose chain ends on the hydrophobic face of BC microfibril. With increasing free TrCel7A concentrations the isotherm gradually deviated from the Langmuir's one binding site model. This was caused by the increasing contribution of lower affinity binding modes that included both active site mediated binding and non-productive binding with active site free from cellulose chain. The binding of TrCel7A to BC was found to be only partially reversible. Furthermore, the isotherm was dependent on the concentration of BC with more efficient binding observed at lower BC concentrations. The phenomenon can be ascribed to the BC concentration dependent aggregation of BC microfibrils with concomitant reduction of specific surface area.

Surface esterification of cellulose nanofibers by a simple organocatalytic methodology

Bacterial cellulose nanofibers were esterified with two short carboxylic acids by means of a simple and novel organic acid-catalyzed route. The methodology proposed relayed on the use of a non-toxic biobased α-hydroxycarboxylic acid as catalyst, and proceeded under moderate reaction conditions in solventless medium. By varying the esterification interval, acetylated and propionized bacterial cellulose nanofibers with degree of substitution (DS) in the 0.02–0.45 range could be obtained. Esterified bacterial cellulose samples were characterized by means of Solid-State CP/MAS 13C Nuclear Magnetic Resonance spectroscopy (CP/MAS 13C NMR), Fourier Transform Infrared spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and chosen hydrophobicity test assays. TGA results showed that the esterified nanofibers had increased thermal stability, whereas XRD data evidenced that the organocatalytic esterification protocol did not alter their crystallinity. The analysis of the ensuing modified nanofibers by NMR, FTIR, XRD and TGA demonstrated that esterification occurred essentially at the surface of bacterial cellulose microfibrils, something highly desirable for changing their surface hydrophilicity while not affecting their ultrastructure.

Utilization of Makgeolli Sludge Filtrate (MSF) as Low-Cost Substrate for Bacterial Cellulose Production by Gluconacetobacter xylinus

Search for efficient low-cost substrate/additives are gaining significant impetus in bacterial cellulose (BC) production. Makgeolli sludge (a traditional Korean wine distillery waste) is enriched with organic acid, alcohol, and sugar. Using makgeolli sludge filtrate (MSF) and Hestrin-Schramm (HS) medium (g/l of distilled water: glucose, 10.0; peptone, 5.0; yeast extract, 5.0; disodium phosphate, 2.7; citric acid, 1.15; pH 5.0), two different media-namely the modified HS media (ingredients of HS media except glucose dissolved in MSF) and mixed modified HS media (equal volume mixture of original and modified HS media)-were formulated. BC production with Gluconacetobacter xylinus was studied using the two above referred medium. Keeping HS medium as reference, effect of initial pH, glucose, ethanol, and organic acid concentration on BC production was also studied. It suggests that increasing initial glucose (up to 25 g/l) though improves BC production but results in poor BC yield above 15 g/l of glucose. However, addition of alcohol (up to 1%v/v) or citric acid (up to 20 mM) escalate productivity up to four and two times, respectively. In both modified HS media and mixed modified HS medium, BC production was four to five times higher than that of original HS medium. Even MSF alone surpassed HS medium in BC production. Scanning electron microscopy showed that BC microfibrils from MSF based media were several micrometers long and about 25-60 nm widths. X-ray diffraction patterns suggested the produced BC were of cellulose I polymorph.