Bone morphogenetic protein signaling inhibitor improves differentiation and function of 3D muscle construct fabricated using C2C12

Functional tissue-engineered artificial skeletal muscle tissue has great potential for pharmacological and academic applications. This study demonstrates an in vitro tissue engineering system to construct functional artificial skeletal muscle tissues using self-organization and signal inhibitors. To induce efficient self-organization, we optimized the substrate stiffness and extracellular matrix (ECM) coatings. We modified the tissue morphology to be ring-shaped under optimized self-organization conditions. A bone morphogenetic protein (BMP) inhibitor was added to improve overall myogenic differentiation. This supplementation enhanced the myogenic differentiation ratio and myotube hypertrophy in two-dimensional cell cultures. Finally, we found that myotube hypertrophy was enhanced by a combination of self-organization with ring-shaped tissue and a BMP inhibitor. BMP inhibitor treatment significantly improved myogenic marker expression and contractile force generation in the self-organized tissue. These observations indicated that this procedure may provide a novel and functional artificial skeletal muscle for pharmacological studies.

Production of 3-Hydroxytyrosol from Glucose by Chromosomally Engineered Escherichia coli by Fed-Batch Cultivation in a Jar Fermenter

3-Hydroxytyrosol (HT) is a super antioxidant possessing many physiological advantages for human health. However, the extraction of natural HT from olive (Olea europaea) is expensive, and its chemical synthesis presents an environmental burden. Therefore, microbial production of HT from renewable sources has been investigated over the past decade. In the present study, we modified the chromosome of a phenylalanine-producing strain of Escherichia coli to generate an HT-producing strain. The initial strain showed good HT production in tests performed by test tube cultivation, but this performance did not transfer to jar-fermenter cultivation. To grow well and achieve higher titers, the chromosome was further engineered and the cultivation conditions were further modified. The final strain achieved a higher HT titer (8.8 g/L) and yield (8.7%) from glucose in the defined synthetic medium. These yields are the best reported to date for the biosynthesis of HT from glucose.

Engineered whole cut meat-like tissue by the assembly of cell fibers using tendon-gel integrated bioprinting

With the current interest in cultured meat, mammalian cell-based meat has mostly been unstructured. There is thus still a high demand for artificial steak-like meat. We demonstrate in vitro construction of engineered steak-like tissue assembled of three types of bovine cell fibers (muscle, fat, and vessel). Because actual meat is an aligned assembly of the fibers connected to the tendon for the actions of contraction and relaxation, tendon-gel integrated bioprinting was developed to construct tendon-like gels. In this study, a total of 72 fibers comprising 42 muscles, 28 adipose tissues, and 2 blood capillaries were constructed by tendon-gel integrated bioprinting and manually assembled to fabricate steak-like meat with a diameter of 5 mm and a length of 10 mm inspired by a meat cut. The developed tendon-gel integrated bioprinting here could be a promising technology for the fabrication of the desired types of steak-like cultured meats.

Microarray profiling of gene expression in C2C12 myotubes trained by electric pulse stimulation

Electric pulse-stimulated C2C12 myotubes are gaining interest in the field of muscle physiology and biotechnology because electric pulse stimulation (EPS) enhances sarcomere structure development and active tension generation capability. Recently, we found that termination of EPS results in the rapid loss of active tension generation accompanied by disassembly of the sarcomere structure, which may represent an in vitro muscle atrophy model. To elucidate the molecular mechanism underlying this rapid loss of active tension generation and sarcomere structure disassembly after termination of EPS, we performed transcriptomic analysis using microarray. After termination of EPS, 74 genes were upregulated and 120 genes were downregulated after 30 min; however, atrophy-related genes were not found among these genes. To further assess the effect of EPS on gene expression, we re-applied EPS after its termination for 8 h and searched for genes whose expression was reversed. Four genes were upregulated by termination of EPS and downregulated by the re-application of EPS, whereas two genes were downregulated by termination of EPS and upregulated by the re-application of EPS. Although none of these genes were atrophy- or hypertrophy-related, the results presented in this study will contribute to the understanding of gene expression changes that mediate rapid loss of active tension generation and sarcomere structure disassembly following termination of EPS in C2C12 myotubes.

Effect of hydrogen peroxide concentration on the maintenance and differentiation of cultured skeletal muscle cells

We have studied the effects of hydrogen peroxide (H₂O₂) on the differentiation and maintenance of C2C12 myoblasts. The effects of H₂O₂ were evaluated by cell viability, total protein concentration, the relative amount of muscle-related proteins, sarcomere structure, and active tension generation. Oxidative stress is one of the major causes of myopathy after exercise and thus establishing the method to evaluate the effects on muscle function is essential. The primary function of striated muscle is to generate force, thus, the measurement of active tension is important in assessing the effect of chemicals on muscle. Among the indices we tested, the sarcomere structure was the most sensitive to the H₂O₂ exposure while the cell viability was less sensitive. The effects of H₂O₂ on active tension correlated with a decrease in the amount of muscle proteins. In this study, our results showed that the effect of chemicals on muscle should be measured in multiple ways, including active tension generation, for a better understanding of its physiological impact.

Effect of cell-extracellular matrix interaction on myogenic characteristics and artificial skeletal muscle tissue

Although various types of artificial skeletal muscle tissue have been reported, the contractile forces generated by tissue-engineered artificial skeletal muscles remain to be improved for biological model and clinical applications. In this study, we investigated the effects of extracellular matrix (ECM) and supplementation of a small molecule, which has been reported to enhance α7β1 integrin expression (SU9516), on cell migration speed, cell fusion rate, myoblast (mouse C2C12 cells) differentiation and contractile force generation of tissue-engineered artificial skeletal muscles. When cells were cultured on varying ECM coated-surfaces, we observed significant enhancement in the migration speed, while the myotube formation (differentiation ratio) decreased in all except for cells cultured on Matrigel coated-surfaces. In contrast, SU9516 supplementation resulted in an increase in both the myotube width and differentiation ratio. Following combined culture with a Matrigel-coated surface and SU9516 supplementation, myotube width was further increased. Additionally, contractile forces produced by the tissue-engineered artificial skeletal muscles was augmented following combined culture. These findings indicate that regulation of the cell-ECM interaction is a promising approach to improve the function of tissue-engineered artificial skeletal muscles.

Size- and time-dependent growth properties of human induced pluripotent stem cells in the culture of single aggregate

Aggregate culture of human induced pluripotent stem cells (hiPSCs) is a promising method to obtain high number of cells for cell therapy applications. This study quantitatively evaluated the effects of initial cell number and culture time on the growth of hiPSCs in the culture of single aggregate. Small size aggregates ((1.1 ± 0.4) × 10¹-(2.8 ± 0.5) × 10¹ cells/aggregate) showed a lower growth rate in comparison to medium size aggregates ((8.8 ± 0.8) × 10¹-(6.8 ± 1.1) × 10² cells/aggregate) during early-stage of culture (24-72 h). However, when small size aggregates were cultured in conditioned medium, their growth rate increased significantly. On the other hand, large size aggregates ((1.1 ± 0.2) × 10³-(3.5 ± 1.1) × 10³ cells/aggregate) showed a lower growth rate and lower expression level of proliferation marker (ki-67) in the center region of aggregate in comparison to medium size aggregate during early-stage of culture. Medium size aggregates showed the highest growth rate during early-stage of culture. Furthermore, hiPSCs proliferation was dependent on culture time because the growth rate decreased significantly during late-stage of culture (72-120 h) at which point collagen type I accumulated on the periphery of aggregate, suggesting blockage of diffusive transport of nutrients, oxygen and metabolites into and out of the aggregates. Consideration of initial cell number and culture time are important to maintain balance between autocrine factors secretion and extracellular matrix accumulation on the aggregate periphery to achieve optimal growth of hiPSCs in the culture of single aggregate.

Culture medium refinement by dialysis for the expansion of human induced pluripotent stem cells in suspension culture

Human induced pluripotent stem cells (hiPSCs) secrete essential autocrine factors that are removed along with toxic metabolites when the growth medium is exchanged daily. In this study, after determining the minimum inhibitory level of lactic acid for hiPSCs, a medium refining system was constructed by which toxic metabolites were removed from used culture medium and autocrine factors as well as other growth factors were recycled. Specifically, about 87 % of the basic fibroblast growth factor and 80 % of transforming growth factor beta 1 were retained in the refined medium after dialysis. The refined medium efficiently potentiated the proliferation of hiPS cells in adherent culture. When the refining system was used to refresh medium in suspension culture, a final cell density of (1.1 ± 0.1) × 10⁶ cells mL^-1 was obtained, with 99.5 ± 0.2 % OCT 3/4 and 78.3 ± 1.1 % TRA-1-60 expression, on day 4 of culture. These levels of expression were similar to those observed in the conventional suspension culture. With this method, culture medium refinement by dialysis was established to remove toxic metabolites, recycle autocrine factors as well as other growth factors, and reduce the use of macromolecules for the expansion of hiPSCs in suspension culture.

Induction of functional tissue-engineered skeletal muscle constructs by defined electrical stimulation

Electrical impulses are necessary for proper in vivo skeletal muscle development. To fabricate functional skeletal muscle tissues in vitro, recapitulation of the in vivo niche, including physical stimuli, is crucial. Here, we report a technique to engineer skeletal muscle tissues in vitro by electrical pulse stimulation (EPS). Electrically excitable tissue-engineered skeletal muscle constructs were stimulated with continuous electrical pulses of 0.3 V/mm amplitude, 4 ms width, and 1 Hz frequency, resulting in a 4.5-fold increase in force at day 14. In myogenic differentiation culture, the percentage of peak twitch force (%Pt) was determined as the load on the tissue constructs during the artificial exercise induced by continuous EPS. We optimized the stimulation protocol, wherein the tissues were first subjected to 24.5%Pt, which was increased to 50-60%Pt as the tissues developed. This technique may be a useful approach to fabricate tissue-engineered functional skeletal muscle constructs.

Endothelial cell behavior inside myoblast sheets with different thickness

Using a cell sheet stacking method, we developed an in vitro culture system in which green fluorescent protein expressing human umbilical vein endothelial cells (GFP-HUVECs) were cultured under human skeletal muscle myoblast (HSMM) sheets with different layer numbers. Our aim in developing this system was to examine the different endothelial behaviors in the cell sheet. During 96 h of incubation, in monolayer HSMM sheet, HUVECs quickly reached the top of the cell sheet and detached. In three-layered HSMM sheet, HUVECs also migrated to the top layer and formed island-shaped aggregates. In five-layered HSMM sheet, HUVECs migrated into the middle of the cell sheet and formed net-shaped aggregates. In seven-layered HSMM sheet, HUVECs migrated in the basal of the cell sheet and formed sparse net-shaped aggregates. The thickness of the HSMM sheet, which can be controlled by the layer number of the cell sheet, is therefore an important parameter that affects the migration time, encounters, localization, and morphology of HUVECs inside the HSMM sheet.

Fed-batch system for cultivating genetically engineered yeast that produces lactic acid via the fermentative promoter

A simple fed-batch system for cultivating genetically engineered yeast generating lactate under the regulation of the PDC1 promoter was established. Traditional strategies that avoid occurrence of Crabtree effect, such as respiratory quotient (RQ) control or ethanol control, are not applicable to the strain because of reduced generation of ethanol and CO(2) by-products. In this system, the feed rate increased when the pH was >5.0, and decreased when the pH was <5.0. Using this system, cell yields on sucrose increased by approximately 30% compared to that with the conventional RQ control method, due to the early detection of occurrence of Crabtree effect by pH decrease.

Enhanced contractile force generation by artificial skeletal muscle tissues using IGF-I gene-engineered myoblast cells

The aim of this study was to investigate whether insulin-like growth factor (IGF)-I gene delivery to myoblast cells promotes the contractile force generated by hydrogel-based tissue-engineered skeletal muscles in vitro. Two retroviral vectors allowing doxycycline (Dox)-inducible expression of the IGF-I gene were transduced into mouse myoblast C2C12 cells to evaluate the effects of IGF-I gene expression on these cells. IGF-I gene expression stimulated the proliferation of C2C12 cells, and a significant increase in the growth rate was observed for IGF-I-transduced C2C12 cells with Dox addition, designated C2C12/IGF (Dox+) cells. Quantitative morphometric analyses showed that the myotubes induced from C2C12/IGF (Dox+) cells had a larger area and a greater width than control myotubes induced from normal C2C12 cells. Artificial skeletal muscle tissues were prepared from the respective cells using hydrogels composed of type I collagen and Matrigel. Western blot analyses revealed that the C2C12/IGF (Dox+) tissue constructs showed activation of a skeletal muscle hypertrophy marker (Akt) and enhanced expression of muscle-specific markers (myogenin, myosin heavy chain and tropomyosin). Moreover, the creatine kinase activity was increased in the C2C12/IGF (Dox+) tissue constructs. The C2C12/IGF (Dox+) tissue constructs contracted in response to electrical pulses, and generated a significantly higher physical force than the control C2C12 tissue constructs. These findings indicate that IGF-I gene transfer has the potential to yield functional skeletal muscle substitutes that are capable of in vivo restoration of the load-bearing function of injured muscle or acting as in vitro electrically-controlled bio-actuators.

Fabrication of scaffold-free contractile skeletal muscle tissue using magnetite-incorporated myogenic C2C12 cells

We have fabricated a functional skeletal muscle tissue using magnetite-incorporated myogenic cell line C2C12 and a magnetic field. Magnetite-incorporated C2C12 cells were patterned linearly on a monolayer of fibroblast NIH3T3 cells, using a magnetic field concentrator. After induction of differentiation, the C2C12 cells fused and formed multi-nucleated myotubes. The 3T3 layer became detached in a sheet-like manner after cultivation in differentiation medium for 5-8 days. When two separate collagen films were placed on a culture dish as tendon structures, a cylindrical construct was formed. Histological observation of the fabricated cylindrical tissue revealed the presence of multinucleate cells within it. Immunofluorescence staining of the construct showed the presence of sarcomere structures within the construct. Western blot analysis showed that muscle proteins were expressed in the construct. When the construct was stimulated with electric pulses, it exhibited active tension of approximately 1 microN. These results demonstrate that functional skeletal muscle tissue was formed through magnetic force-based tissue engineering. This is the first report of fabrication of skeletal muscle tissue with active tension-generating capability using magnetic force-based tissue engineering. The scaffold-free skeletal muscle tissue engineering technique presented in this study will be useful for regenerative medicine, drug screening or use as a bio-actuator.

Evaluation of serum-free differentiation conditions for C2C12 myoblast cells assessed as to active tension generation capability

We have compared several serum-free media for the differentiation of C2C12 myoblasts and assessed the extent of differentiation in several ways including as to active tension generation capability. C2C12 cells were allowed to differentiate in Dulbecco's modified Eagle's medium (DMEM) containing Ham's F-12 (F-12), AIM-V (AIM), 0.2% Ultroser-G in DMEM (Ult-G), and 0.1% Sericin in DMEM (Sericin), compared with in DMEM supplemented with 2% horse serum (HS) or 2% calf serum (CS). C2C12 differentiation was assessed as the extent of myotube formation, glucose metabolism, protein expression, sarcomere formation, and active tension generation. All serum-free media examined were capable of inducing myotube formation and the expression of muscle-specific proteins. All serum-free media except for F-12 gave the sarcomere structure. Active tension generation was observed for cells that differentiated in AIM and Ult-G, but the active tension generated by C2C12 cells that differentiated in Ult-G was only ∼25% in the case of myotubes that formed in HS. The addition of Ult-G to the AIM resulted in improvement of the active tension generation capability, the active tension generated being ∼3.4× compared to that in HS. The approach for assessing muscle cell differentiation presented in this study will be suitable for other studies that involve the differentiation of muscle cells.

Oxygen plasma-treated thermoresponsive polymer surfaces for cell sheet engineering

Although cell sheet tissue engineering is a potent and promising method for tissue engineering, an increase of mechanical strength of a cell sheet is needed for easy manipulation of it during transplantation or 3D tissue fabrication. Previously, we developed a cell sheet-polymer film complex that had enough mechanical strength that can be manipulated even by tweezers (Fujita et al., 2009. Biotechnol Bioeng 103(2): 370-377). We confirmed the polymer film involving a temperature sensitive polymer and extracellular matrix (ECM) proteins could be removed by lowering temperature after transplantation, and its potential use in regenerative medicine was demonstrated. However, the use of ECM proteins conflicted with high stability in long-term storage and low cost. In the present study, to overcome these drawbacks, we employed the oxygen plasma treatment instead of using the ECM proteins. A cast and dried film of thermoresponsive poly-N-isopropylacrylamide (PNIPAAm) was fabricated and treated with high-intensity oxygen plasma. The cells became possible to adhere to the oxygen plasma-treated PNIPAAm surface, whereas could not to the inherent surface of bulk PNIPAAm without treatment. Characterizations of the treated surface revealed the surface had high stability. The surface roughness, wettability, and composition were changed, depending on the plasma intensity. Interestingly, although bulk PNIPAAm layer had thermoresponsiveness and dissolved below lower critical solution temperature (LCST), it was found that the oxygen plasma-treated PNIPAAm surface lost its thermoresponsiveness and remained insoluble in water below LCST as a thin layer. Skeletal muscle C2C12 cells could be cultured on the oxygen plasma-treated PNIPAAm surface, a skeletal muscle cell sheet with the insoluble thin layer could be released in the medium, and thus the possibility of use of the cell sheet for transplantation was demonstrated.

Novel method for measuring active tension generation by C2C12 myotube using UV-crosslinked collagen film

We have developed a novel method for measuring active tension generated by cultured myotubes using UV-crosslinked collagen film. Skeletal myoblasts cell line C2C12 or human primary skeletal myoblasts were seeded onto a thin (35 microm) collagen film strip, on which they proliferated and upon induction of differentiation they formed multinucleated myotubes. The collagen film-myotube complex contracted upon electric pulse stimulation which could be observed by light microscope. When collagen film-myotube complex were attached to force transducer, active tension generation was observed upon electric pulse stimulation. Measurement of active tension was possible for multiple times for more than 1 month with the same batch of collagen film-myotube complex. Active tension generation capability of C2C12 myotubes increased with progression of differentiation, reaching maximal value 6 days after induction of differentiation. Using this method, we measured the effect of artificial exercise induced by electric pulse on active tension generation capability of C2C12 myotubes. When the electric pulses of 1 Hz were continuously applied to induce artificial exercise, the active tension augmentation was observed. After 1 week of artificial exercise, the active tension reached approximately 10x of that before the exercise. The increased active tension is attributable to the formation of the sarcomere structure within the myotubes and an increased amount of myotubes on the collagen film. The increased amount of myotubes is possibly due to the suppressed atrophy of myotubes by enhanced expression of Bcl-2.

Preparation of artificial skeletal muscle tissues by a magnetic force-based tissue engineering technique

Artificial muscle tissues composed of mouse myoblast C2C12 cells were prepared using a magnetic force-based tissue engineering technique. C2C12 cells labeled with magnetite nanoparticles were seeded into the wells of 24-well ultralow-attachment culture plates. When a magnet was positioned underneath each plate, the cells accumulated evenly on the culture surface and formed multilayered cell sheets. Since the shapes of artificial tissue constructs can be controlled by magnetic force, cellular string-like assemblies were formed by using a linear magnetic field concentrator with a magnet. However, the resulting cellular sheets and strings shrank considerably and did not retain their shapes during additional culture periods for myogenic differentiation. On the other hand, when a silicone plug was positioned at the center of the well during the fabrication of a cell sheet, the cell sheet shrank drastically and formed a ring-like assembly around the plug. A histological examination revealed that the cells in the cellular ring were highly oriented in the direction of the circumference by the tension generated within the structure. Individual cellular rings were hooked around two pins separated by 10 mm, and successfully cultured for 6 d without breakage. After a 6-d culture in differentiation medium, the C2C12 cells differentiated to form myogenin-positive multinucleated myotubes. Highly dense and oriented skeletal muscle tissues were obtained using this technique, suggesting that this procedure may represent a novel strategy for muscle tissue engineering.

Enhancement of C2C12 differentiation by perfluorocarbon-mediated oxygen delivery

We have studied the effect of enhanced oxygen delivery by perfluorocarbons on the differentiation of C2C12 cells. The extent of differentiation was assessed by means of phase contrast/fluorescence microscopy, active tension measurement and the glucose consumption/lactate production rates. We found that enhanced oxygen delivery is suitable for full differentiation of C2C12 cells.

Micropatterning of single myotubes on a thermoresponsive culture surface using elastic stencil membranes for single-cell analysis

We have developed a micropatterning procedure for single myotubes and demonstrated recovery of patterned myotubes without the use of methods that might cause damage to the cells. Since skeletal muscle is a highly ordered tissue mainly composed of myotubes, analysis of single myotubes is one of the promising approaches for studying the various diseases related to skeletal muscle tissues. However, the analysis of single myotubes is quite complicated because of the difficulty in distinguishing individual myotubes differentiated on a normal cell culture surface. In the present study, thin polydimethylsiloxane (PDMS) membranes, which have rectangular holes (30, 50, 100, and 200 microm in width; 500, 750, and 1000 microm in length) through them, were fabricated by using a photolithography technique and used for single myotube micropatterning. A bovine serum albumin-coated (BSA-coated) stencil membrane was placed on a cell culture surface and C2C12 myoblasts were seeded on it. Since the cells could not attach to the surface of the stencil membrane, the cell proliferated and differentiated into myotubes in the hole areas specifically. By peeling off the membrane, a micropattern of myotubes was obtained. It was revealed that the optimum width of rectangular holes for a micropattern of single myotubes was between 30 to 50 microm. Furthermore, by placing a membrane on a thermoresponsive culture surface, recovery of the micropatterned myotubes was possible by lowering the temperature. This method involving the stencil membranes and a thermoresponsive culture surface is useful for analyzing subcellular or single myotubes.

Alignment of skeletal muscle myoblasts and myotubes using linear micropatterned surfaces ground with abrasives

Alignment of cells plays a significant key role in skeletal muscle tissue engineering because skeletal muscle tissue in vivo has a highly organized structure consisting of long parallel multinucleated myotubes formed through differentiation and fusion of myoblasts. In the present study, we developed an easy, simple, and low-cost method for aligning skeletal muscle cells by using surfaces with linear microscale features fabricated by grinding. Iron blocks were ground in one direction with three kinds of abrasives (9 microm diamond suspension, #400 sandpaper, and #150 sandpaper) and then used as molds to make micropatterned polydimethylsiloxane (PDMS) substrates (type I, type II, and type III). Observation of the surface topography revealed that the PDMS substrates exhibited different degree of mean roughness (Ra), 0.03 microm for type I, 0.16 microm for type II, and 0.56 microm for type III, respectively. Murine skeletal muscle cell line C2C12 myoblasts were cultured and differentiated on the patterned PDMS substrates, and it was examined whether the alignment of C2C12 myoblasts and myotubes was possible. Although the cell growth and differentiation on the three types of patterned substrates were similar to those on the flat PDMS substrate as a control, the alignment of both C2C12 myoblasts and myotubes was obviously observed on types II and III, but not on type I or the control substrate. These results indicate that surfaces ground with abrasives will be useful for fabricating aligned skeletal muscle tissues.

The effect of pyruvate decarboxylase gene knockout in Saccharomyces cerevisiae on L-lactic acid production

A plant- and crop-based renewable plastic, poly-lactic acid (PLA), is receiving attention as a new material for a sustainable society in place of petroleum-based plastics. We constructed a metabolically engineered Saccharomyces cerevisiae that has both pyruvate decarboxylase genes (PDC1 and PDC5) disrupted in the genetic background to express two copies of the bovine L-lactate dehydrogenase (LDH) gene. With this recombinant, the yield of lactate was 82.3 g/liter, up to 81.5% of the glucose being transformed into lactic acid on neutralizing cultivation, although pdc1 pdc5 double disruption led to ineffective decreases in cell growth and fermentation speed. This strain showed lactate productivity improvement as much as 1.5 times higher than the previous strain. This production yield is the highest value for a lactic acid-producing yeast yet reported.

d-Lactic acid production by metabolically engineered Saccharomyces cerevisiae

Poly D-lactic acid is an important polymer because it improves the thermostability of poly L-lactic acid by the stereo complex formation. We constructed a metabolically engineered Saccharomyces cerevisiae that produces D-lactic acid efficiently. In this recombinant, the coding region of pyruvate decarboxylase 1 (PDC1) was completely deleted, and two copies of the D-lactate dehydrogenase (D-LDH) gene from Leuconostoc mesenteroides subsp. mesenteroides strain NBRC3426 were introduced into the genome. The D-lactate production reached 61.5 g/l, the amount of glucose being transformed into D-lactic acid being 61.2% under neutralizing conditions. Additionally, the yield of free D-lactic acid was also shown to be 53.0% under non-neutralizing conditions. It was confirmed that D-lactic acid of extremely high optical purity of 99.9% or higher. Our finding obtained the possibility of a new approach for pure d-lactic acid production without a neutralizing process compared with other techniques involving lactic acid bacteria and transgenic Escherichia coli.

Metabolic engineering of Saccharomyces cerevisiae for efficient production of pure L-(+)-lactic acid

We developed a metabolically engineered Saccharomyces cerevisiae, which produces optically pure L-lactic acid efficiently using cane juice-based medium. In this recombinant, the coding region of pyruvate decarboxylase (PDC)1 was completely deleted, and six copies of the bovine L-lactate dehydrogenase (L-LDH) genes were introduced on the genome under the control of the PDC1 promoter. To confirm optically pure lactate production in low-cost medium, cane juice-based medium was used in fermentation with neutralizing conditions. L-lactate production reached 122 g/L, with 61% of sugar being transformed into L-lactate finally. The optical purity of this L-lactate, that affects the physical characteristics of poly-L-lactic acid, was extremely high, 99.9% or over.

A novel gene delivery system in plants with calcium alginate micro-beads

We have produced micrometer-sized calcium alginate beads referred to as "bio-beads" that encapsulate plasmid DNA molecules carrying a reporter gene. In order to evaluate the efficiency of the bio-beads in mediating genetic transfection, protoplasts isolated from cultured tobacco cells (BY-2) were transfected with bio-beads containing a plasmid that carries the modified green fluorescent protein gene CaMV35S-sGFP. With the bio-beads treatment, approximately ten-fold higher GFP expression was observed after 24 h incubation compared to that with the conventional method using a naked plasmid solution. Transfection was up to 0.22% efficient. These results indicate that bio-beads have a possibility for efficient transformation in plants.

Enhanced anthocyanin production from grape callus in an air-lift type bioreactor using a viscous additive-supplemented medium

An N-medium containing carboxymethyl cellulose (CMC) was applied to an air-lift type bioreactor culture of grape (Vitis vinifera cv. Bailey alicant A.) callus, and anthocyanin production was investigated. Grape callus grew well at an air flow rate of 80 ml/min and anthocyanin production was significantly increased in the N-medium, reaching 17 mg/l after 7 d of culture. The anthocyanin content of the N-medium was about two times higher than that of the conventional medium without CMC. The effect of air flow rate was also investigated within the range from 40 to 160 ml/min. A twofold increase in anthocyanin content was obtained at all the air flow rates tested in the N-medium. The distribution of grape callus size obtained after 7 d of the bioreactor culture was investigated. The average callus size was 490 mum which was 1.6 times larger than that obtained in the conventional medium. It was found that large calli with a relatively high anthocyanin pigment content were formed in the bioreactor culture using the N-medium. The fluid dynamics in the bioreactor was also investigated at three points (top, middle and bottom) in the bioreactor by laser doppler velocimetry. The average axial velocity of the circulated medium was 0.4 times lower than that of the conventional medium while their average radial velocities were almost the same (zero). The standard deviation of radial velocity fluctuation in the N-medium was also 0.4 times less than that in the conventional medium. These results suggest that turbulent flow occurred in the bioreactor culture using the conventional medium and the degree of turbulent flow decreased significantly when 0.8% CMC was added to the medium to prepare the N-medium. A change of the flow pattern is considered to be the cause of the decrease in hydrodynamic stress, resulting in enhanced pigment production due to the enlargement of the callus.

A novel transfection method for mammalian cells using calcium alginate microbeads

The direct transfer of genetic materials into mammalian cells is an indispensable technique. We have developed calcium alginate (CA) microbeads which can deliver plasmid DNAs and yeast artificial chromosomes into plant and yeast cells. In this paper, we demonstrate the effective transfection of mammalian cells by CA microbeads immobilizing plasmid DNAs. The transfection was performed using the pEGFP-C1 plasmid containing the cytomegalovirus (CMV) promoter and enhanced green fluorescent protein (EGFP) gene. The transient expression of EGFP was observed 24 h after transfection. The expression efficiency was maximum when the concentration of sodium alginate was 1% and the amount of plasmid DNA was increased to 100 microg. The expression efficiency of our method using CA microbeads is 2-10 times higher than that of the polyethylene glycol (PEG) method. Our results suggest that the CA microbead mediated transfection of mammalian cells effectively delivers genetic materials into mammalian suspension cells.

Enhanced and prolonged production of plantlets regenerated from carrot callus in a viscous additive-supplemented medium

To reduce the hydrodynamic stress in plant cell culture and enhance the production of regenerated plantlets, a liquid medium containing a viscous additive was newly designed and plantlet production from embryogenic carrot callus cultivated in the medium was examined. Na-alginate or carboxymethyl cellulose (CMC) was used as the viscous additive. The viscosity of the medium increased with increasing additive content and the number of regenerated plantlets also increased. When carrot calli were cultivated in the medium containing 0.4% CMC, designated as N medium (viscosity, 3 mPa.s), the maximum enhancement of plantlet regeneration, approximately 2.5 times higher than that in the control medium, was obtained. Enlargement of callus size observed in N medium is considered to be the main reason for the enhanced plantlet regeneration. Regeneration enhancement was sufficiently induced after calli were cultivated once in N medium, but this regeneration ability rapidly disappeared after once cultivation in the conventional medium. In repeated batch culture using N medium, plantlet production continued at a high level for 18 batches (250 d) with no significant decrease, while in the control culture without CMC the number of plantlets produced dropped to almost zero by the sixth batch (84 d).

Lipase production in two-step fed-batch culture of organic solvent-tolerant Pseudomonas aeruginosa LST-03

Efficient lipase production by two-step fed-batch culture of an organic solvent-tolerant bacterium, Pseudomonas aeruginosa LST-03, was investigated. When FB synthetic medium was used in flask culture, no lipase activity was detected, whereas lipase was produced at 2.3 I.U./ml in C2 complex medium. However, lipase production was induced in FB medium when a fatty acid was added to the culture broth in the stationary phase. Among fatty acids tested, long chain saturated fatty acids, such as C18 (stearic acid) and C20 (arachidic acid), were found to function as effective inducers for the production of lipase, giving an activity level almost the same as that obtained in C2 medium in flask culture. Two-step lipase production, comprised of a growth phase in fed-batch mode and a production phase in which lipase was induced by the addition of 5% (v/v) stearic acid, was carried out in a jar-fermentor. In the growth phase, the maximum cell concentration at 16 h was only 20 in terms of the optical density at 660 nm (OD660), and a low level of lipase production (8 I.U./ml) was obtained after 167 h. This was considered to be due to the exhaustion of several medium components brought about by the use of an unsuitable medium or feeding solution. After analyzing the contents of the compounds in the culture broth by inductively coupled plasma spectrometry for metal ions and HPLC for anions, a modified FB medium was designed. When this modified FB medium was used in two-step fed-batch culture, the maximum cell concentration reached an OD660 of 55 (30.2 g-dry cells/l) at 16.5 h, and lipase was produced at 96 I.U./ml after 35 h, which is approximately 40 times higher than the production level obtained in flask culture using C2 medium.

Efficient production of L-Lactic acid by metabolically engineered Saccharomyces cerevisiae with a genome-integrated L-lactate dehydrogenase gene

We developed a metabolically engineered yeast which produces lactic acid efficiently. In this recombinant strain, the coding region for pyruvate decarboxylase 1 (PDC1) on chromosome XII is substituted for that of the l-lactate dehydrogenase gene (LDH) through homologous recombination. The expression of mRNA for the genome-integrated LDH is regulated under the control of the native PDC1 promoter, while PDC1 is completely disrupted. Using this method, we constructed a diploid yeast transformant, with each haploid genome having a single insertion of bovine LDH. Yeast cells expressing LDH were observed to convert glucose to both lactate (55.6 g/liter) and ethanol (16.9 g/liter), with up to 62.2% of the glucose being transformed into lactic acid under neutralizing conditions. This transgenic strain, which expresses bovine LDH under the control of the PDC1 promoter, also showed high lactic acid production (50.2 g/liter) under nonneutralizing conditions. The differences in lactic acid production were compared among four different recombinants expressing a heterologous LDH gene (i.e., either the bovine LDH gene or the Bifidobacterium longum LDH gene): two transgenic strains with 2microm plasmid-based vectors and two genome-integrated strains.

Genetically engineered wine yeast produces a high concentration of L-lactic acid of extremely high optical purity

For mass production of lactic acid, we newly constructed a transgenic wine yeast strain that included six copies of the bovine L-lactate dehydrogenase gene on the genome. On fermentation in inexpensive cane juice-based medium, L-lactate production of this recombinant reached 122 g/liter and the optical purity was 99.9% or higher.

Obtaining transgenic plants using the bio-active beads method

Several methods of transformation are currently available for delivering exogenous DNA into animal and plant cells. In this study, a novel and efficient transformation system for DNA delivery/expression with a capacity to transport DNA of high molecular weight was developed. This system can overcome the shortcomings of traditional transformation methods such as Agrobacterium-mediated transformation, particle bombardment, and the electroporation method. The method developed in this study uses calcium alginate micro beads to immobilize DNA molecules in combination with polyethylene glycol treatment. In addition, it is simple and low-cost, and requires limited equipment. Using this method, we have successfully transformed tobacco plants, screening by kanamycin resistance. The transformed genes in the transformants were confirmed by PCR and Southern hybridization.

Transformation of yeast using calcium alginate microbeads with surface-immobilized chromosomal DNA

Yeast artificial chromosomes (YACs) are useful cloning vectors that have the capacity to carry large DNA inserts. The largest barrier to using such large DNA molecules in transformation experiments has been their physical instability in solution. We developed a new method of transforming yeast using chromosome-sized DNA. The method uses calcium alginate microbeads to immobilize high-density yeast chromosomal DNA. Chromosomal DNA immobilized on microbeads is physically stabilized compared with naked chromosomal DNA. The microbead-mediated transformation performed well, not only with respect to the transformation frequency with large DNA molecules (>100 kb) but also in successful transformation using split chromosome DNA that exceeded 450 kb.