Cell Recycle System Research Articles

Continuous fermentation using high cell density cell recycle system for L-lactic acid production.

For complete utilization of high glucose at ∼100 g/L, a high cell density (HCD) continuous fermentation system was established using Lb. delbrueckii NCIM 2025 for the bioproduction of lactic acid (LA). An integrated membrane cell recycling system coupled with the continuous bioreactor, aided to achieve the highest 34.77 g/L h LA productivity and 0.94-0.98 g/g yield. ∼34 times higher productivity was observed (in comparison to batch fermentation conducted in this study), when the continuous operations were carried out at the maximum dilution rate and wet cell weight i.e. 0.36 h-1 and 230 g/L, respectively. These results show the potential of this method for large-scale lactic acid production because it not only produces high titers but also ensures that glucose is used effectively. The method's superior performance in comparison to earlier studies suggests it as an affordable and sustainable alternative for the production of LA.

Membrane-based continuous fermentation with cell recycling for propionic acid production from glycerol by Acidipropionibacterium acidipropionici

BackgroundMicrobial production of propionic acid (PA) from renewable resources is limited by the slow growth of the producer bacteria and product-mediated inhibition. The present study evaluates high cell density continuous PA fermentation from glycerol (Gly) using Acidipropionibacterium acidipropionici DSM 4900 in a membrane-based cell recycling system. A ceramic tubular membrane filter of 0.22 μm pore size was used as the filtering device for cell recycling. The continuous fermentations were run sequentially at dilution rates of 0.05 and 0.025 1/h using varying glycerol concentrations and two different yeast extract concentrations.ResultsPA volumetric productivity of 0.98 g/L.h with a product yield of 0.38 gPA/gGly was obtained with 51.40 g/L glycerol at a yeast extract concentration of 10 g/L. Increasing the glycerol and yeast extract concentrations to 64.50 g/L and 20 g/L, respectively, increased in PA productivity, product yield, and concentration to 1.82 g/L.h, 0.79 gPA/gGly, and 38.37 g/L, respectively. However, lowering the dilution rate to 0.025 1/h reduced the production efficiency. The cell density increased from 5.80 to 91.83 gCDW/L throughout the operation, which lasted for a period of 5 months. A tolerant variant of A. acidipropoinici exhibiting growth at a PA concentration of 20 g/L was isolated at the end of the experiment.ConclusionsApplying the current approach for PA fermentation can overcome several limitations for process industrialization.

Fluxograma para diagnóstico precoce, tratamento e monitorização da deficiência de ferro na criança

Iron deficiency anemia is defined as a hemoglobin concentration less than a second standard deviation from the distribution mean for a population of the same sex and age. It is the last event in a progression of negative iron balance, with the stages: negative balance, iron deficiency, and iron deficiency anemia. It is the most common hematologic alteration in the world, especially in developing countries. The main source of iron in the body comes from the red blood cell recycling system, while a smaller portion comes from the diet. Despite this, nutritional deficiency is the main etiology of iron deficiency anemia and iron deficiency in childhood. Iron is essential for several physiological functions and its deficiency, especially in childhood, can compromise mental and physical development. Clinical manifestations usually become detectable in severe deficiency. For this reason, the early diagnosis of iron deficiency is through laboratory tests. It should be performed through screening at 12 months of life. Treatment should be started promptly after diagnosis. Diet is of little value in correcting iron owing to the low bioavailability of iron in most foods. However, preparations containing iron are easily absorbed by the body. Given the severity of this condition, treatment should be monitored using laboratory parameters. This study aims to develop a protocol for screening and monitoring the treatment of iron deficiency anemia to systematize and organize care, bringing better results for the childs development.

FLUXOGRAMA PARA DIAGNÓSTICO PRECOCE, TRATAMENTO E MONITORIZAÇÃO DA DEFICIÊNCIA DE FERRO NA CRIANÇA

Iron deficiency anemia is defined as a hemoglobin concentration less than a second standard deviation from the distribution mean for a population of the same sex and age. It is the last event in a progression of negative iron balance, with the stages: negative balance, iron deficiency, and iron deficiency anemia. It is the most common hematologic alteration in the world, especially in developing countries. The main source of iron in the body comes from the red blood cell recycling system, while a smaller portion comes from the diet. Despite this, nutritional deficiency is the main etiology of iron deficiency anemia and iron deficiency in childhood. Iron is essential for several physiological functions and its deficiency, especially in childhood, can compromise mental and physical development. Clinical manifestations usually become detectable in severe deficiency. For this reason, the early diagnosis of iron deficiency is through laboratory tests. It should be performed through screening at 12 months of life. Treatment should be started promptly after diagnosis. Diet is of little value in correcting iron owing to the low bioavailability of iron in most foods. However, preparations containing iron are easily absorbed by the body. Given the severity of this condition, treatment should be monitored using laboratory parameters. This study aims to develop a protocol for screening and monitoring the treatment of iron deficiency anemia to systematize and organize care, bringing better results for the childs development.

D-Lactic acid production from agricultural residues by membrane integrated continuous fermentation coupled with B vitamin supplementation

Backgroundd-Lactic acid played an important role in the establishment of PLA as a substitute for petrochemical plastics. But, so far, the d-lactic acid production was limited in only pilot scale, which was definitely unable to meet the fast growing market demand. To achieve industrial scale d-lactic acid production, the cost-associated problems such as high-cost feedstock, expensive nutrient sources and fermentation technology need to be resolved to establish an economical fermentation process.ResultsIn the present study, the combined effect of B vitamin supplementation and membrane integrated continuous fermentation on d-lactic acid production from agricultural lignocellulosic biomass by Lactobacillus delbrueckii was investigated. The results indicated the specific addition of vitamins B1, B2, B3 and B5 (VB1, VB2, VB3 and VB5) could reduce the yeast extract (YE) addition from 10 to 3 g/l without obvious influence on fermentation efficiency. By employing cell recycling system in 350 h continuous fermentation with B vitamin supplementation, YE addition was further reduced to 0.5 g/l, which resulted in nutrient source cost reduction of 86%. A maximum d-lactate productivity of 18.56 g/l/h and optical purity of 99.5% were achieved and higher than most recent reports.ConclusionThese findings suggested the novel fermentation strategy proposed could effectively reduce the production cost and improve fermentation efficiency, thus exhibiting great potential in promoting industrial scale d-lactic acid production from lignocellulosic biomass.Graphical

Production of trans-cinnamic acid by whole-cell bioconversion from l-phenylalanine in engineered Corynebacterium glutamicum

Backgroundtrans-cinnamic acid (t-CA) is a phenylpropanoid with a broad spectrum of biological activities including antioxidant and antibacterial activities, and it also has high potential in food and cosmetic applications. Although significant progress has been made in the production of t-CA using microorganisms, its relatively low product titers still need to be improved. In this study, we engineered Corynebacterium glutamicum as a whole-cell catalyst for the bioconversion of l-phenylalanine (l-Phe) into t-CA and developed a repeated bioconversion process.ResultsAn expression module based on a phenylalanine ammonia lyase-encoding gene from Streptomyces maritimus (SmPAL), which mediates the conversion of l-Phe into t-CA, was constructed in C. glutamicum. Using the strong promoter PH36 and ribosome binding site (RBS) (in front of gene 10 of the T7 phage), and a high-copy number plasmid, SmPAL could be expressed to levels as high as 39.1% of the total proteins in C. glutamicum. Next, to improve t-CA production at an industrial scale, reaction conditions including temperature and pH were optimized; t-CA production reached up to 6.7 mM/h in a bioreactor under optimal conditions (50 °C and pH 8.5, using NaOH as base solution). Finally, a recycling system was developed by coupling membrane filtration with the bioreactor, and the engineered C. glutamicum successfully produced 13.7 mM of t-CA (24.3 g) from 18.2 mM of l-Phe (36 g) and thus with a yield of 75% (0.75 mol/mol) through repetitive supplementation.ConclusionsWe developed a highly efficient bioconversion process using C. glutamicum as a biocatalyst and a micromembrane-based cell recycling system. To the best of our knowledge, this is the first report on t-CA production in C. glutamicum, and this robust platform will contribute to the development of an industrially relevant platform for the production of t-CA using microorganisms.

Cilostazol alleviate nicotine induced cardiomyocytes hypertrophy through modulation of autophagy by CTSB/ROS/p38MAPK/JNK feedback loop.

Nicotine is proved to be an important factor for cardiac hypertrophy. Autophagy is important cell recycling system involved in the regulation of cardiac hypertrophy. Cilostazol, which is often used in the management of peripheral vascular disease. However, the effects of cilostazol on nicotine induced autophagy and cardiac hypertrophy are unclear. Here, we aim to determine the role and molecular mechanism of cilostazol in alleviating nicotine-induced cardiomyocytes hypertrophy through modulating autophagy and the underlying mechanisms. Our results clarified that nicotine stimulation caused cardiomyocytes hypertrophy and autophagy flux impairment significantly in neonatal rat ventricular myocytes (NRVMs), which were evidenced by augments of LC3-II and p62 levels, and impaired autophagosomes clearance. Interestingly, cathepsin B (CTSB) activity decreased dramatically after stimulation with nicotine in NRVMs, which was crucial for substrate degradation in the late stage of autophagy process, and cilostazol could reverse this effect dramatically. Intracellular ROS levels were increased significantly after nicotine exposure. Meanwhile, p38MAPK and JNK were activated after nicotine treatment. By using ROS scavenger N-acetyl-cysteine (NAC) could reverse the effects of nicotine by down-regulation the phosphorylation of p38MAPK and JNK pathways, and pretreatment of specific inhibitors of p38MAPK and JNK could restore the autophagy impairment and cardiomyocytes hypertrophy induced by nicotine. Moreover, CTSB activity of lysosome regained after the treatment with cilostazol. Cilostazol also inhibited the ROS accumulation and the activation of p38MAPK and JNK, which providing novel connection between lysosome CTSB and ROS/p38MAPK/JNK related oxidative stress pathway. This is the first demonstration that cilostazol could alleviate nicotine induced cardiomyocytes hypertrophy through restoration of autophagy flux by activation of CTSB and inhibiting ROS/p38/JNK pathway, exhibiting a feedback loop on regulation of autophagy and cardiomyocytes hypertrophy.

PF163 TARGETING LYSOSOMES AS A POTENTIAL THERAPEUTIC APPROACH FOR T‐CELL ACUTE LYMPHOBLASTIC LEUKAEMIA

Background:Tcell acute lymphoblastic leukaemia (T–ALL) is an immature lymphoid tumour characterized by the diffuse infiltration of the bone marrow by malignant lymphoblasts expressing immature T‐cell markers. T–ALL results from a multistep transformation process in which accumulating genetic alterations coordinately disrupt key oncogenic, tumour suppressor and developmental pathways responsible for the normal control of cell growth, proliferation, survival and differentiation during thymocyte development. T‐ALL represents about 15% of paediatric and 25% of adult cases of ALL. The actual treatment for T‐ALL typically consists of a remission‐induction phase, a consolidation phase, and continuation therapy to eliminate residual disease. Recently (Sachlos et al. 2012), dopamine receptor was identified as a possible target for cancer stem cells, validated in acute myeloid leukemia (AML) and breast cancer. We then hypothesized that based on biological similarities between AML and T‐ALL and the existence of leukemic stem cells in both neoplasms, dopamine receptors may constitute a therapeutic target also in T‐ALLAims:The main objective of the study was to validate dopamine receptors as a therapeutic target in T‐ALL.Methods:Dopamine receptor modulators were selected in concordance with the affinity for the dopamine receptor (1‐5). To study the antileukaemic effect of selected drugs, cell viability assays were performed in 3 human T‐ALL cell lines, 1 T‐ALL‐patient‐derived xenograft (PDX), 4 healthy‐donor buffy coats and 5 umbilical cord blood samples. In vivo studies were performed with conditioned adult NOD.Cg‐Prkdc scid Il2rg tm1Wjl /SzJ (NSG) mice xenotransplanted with T‐ALL PDX or cord blood cells treated with dopamine receptor antagonists for 18 h and engraftment levels were determined after 3 or 8 week respectively. The effect on lysosomes and autophagy was determined using the lysotracker and CytoID stainings by flow cytometry and fluorescence microscopy.Results:Among all subtype‐specific dopamine receptor modulators, only antagonists specific for dopamine receptor type 4 (DR4) (L741‐742, Nemonapride, RBI 257) significantly reduced cell viability in T‐ALL cells in the low microMolar range, while no effect on healthy cells was observed. In vivo studies further confirmed the differential antileukaemic effect, as the treatment with L741‐742 significantly reduced leukaemic engraftment, while sparing normal haematopoiesis.T‐ALL cell lines lacked the expression of DR4 on the surface; thus, we searched for an alternative mechanism of action. Our data demonstrated that these drugs produced an expansion of the lysosomal compartment and consequently the failure of the cell recycling system, this induced an overactivation of autophagy and the disruption of cell homestasis, eventually leading to cell death. These 3 antileukaemic DR4 antagonists shared cationic amphiphilic properties, known to induce tropism towards lysosomes, thus providing an explanation for early drug‐induced events, which could ultimately activate the autophagy‐dependent cell death program.Summary/Conclusion:A group of DR4 antagonists selectively eliminates T‐ALL cells, targeting the lysosomal compartment in a dopamine receptor‐independent manner. This organelle disruption leads to the activation of the autophagy‐dependent cell death program. Interestingly, these drugs have little effects in healthy blood cells. Therefore, our results support the further preclinical development of these drugs as potential treatments for T‐ALL.

Continuous bioreactor with cell recycle using tubular ceramic membrane for simultaneous wastewater treatment and bio-oil production by oleaginous Rhodococcus opacus

Rapid consumption of fossil fuels has led to the search for alternative energy sources. Bio-fuels as an alternative energy source require cheap and abundantly available substrates to keep the economics of the production process low. The present study was therefore focused on utilizing raw refinery wastewater by the oleaginous bacterium Rhodococcus opacus for converting it into bio-oil via hydrothermal liquefaction of the lipid rich biomass produced during the treatment process. For treating the wastewater, different operating modes using a bioreactor were evaluated including batch, fed-batch, sequential batch, continuous and continuous with cell recycle using low cost tubular ceramic membrane. Among the different strategies, the continuous cell recycle system proved efficient in terms of complete removal of chemical oxygen demand (COD) (99%) and high lipid production (86%, w/w) at a hydraulic retention time (HRT) of 16 h (dilution rate of 0.06 h−1). Furthermore, the residual bacterial biomass from the bioreactor was treated by HTL to produce bio-oil which showed excellent bio-fuel properties. This study demonstrated the application of R. opacus for simultaneous wastewater treatment and production of bio-oil for energy application.

Enhanced microbial lipid production by Cryptococcus albidus in thehigh-cell-density continuous cultivation with membrane cell recycling and two-stage nutrient limitation.

As a potential feedstock for biofuel production, a high-cell-density continuous culture for the lipid production by Cryptococcus albidus was investigated in this study. The influences of dilution rates in the single-stage continuous cultures were explored first. To reach a high-cell-density culture, a single-stage continuous culture coupled with a membrane cell recycling system was carried out at a constant dilution rate of 0.36/h with varied bleeding ratios. The maximum lipid productivity of 0.69g/L/h was achieved with the highest bleeding ratio of 0.4. To reach a better lipid yield and content, a two-stage continuous cultivation was performed by adjusting the C/N ratio in two different stages. Finally, a lipid yield of 0.32g/g and lipid content of 56.4% were obtained. This two-stage continuous cultivation, which provided a higher lipid production performance, shows a great potential for an industrial-scale biotechnological production of microbial lipids and biofuel production.

Autophagy in turnover of lipid stores: trans-kingdom comparison.

Lipids and their cellular utilization are essential for life. Not only are lipids energy storage molecules, but their diverse structural and physical properties underlie various aspects of eukaryotic biology, such as membrane structure, signalling, and trafficking. In the ever-changing environment of cells, lipids, like other cellular components, are regularly recycled to uphold the housekeeping processes required for cell survival and organism longevity. The ways in which lipids are recycled, however, vary between different phyla. For example, animals and plants have evolved distinct lipid degradation pathways. The major cell recycling system, autophagy, has been shown to be instrumental for both differentiation of specialized fat storing-cells, adipocytes, and fat degradation in animals. Does plant autophagy play a similar role in storage and degradation of lipids? In this review, we discuss and compare implications of bulk autophagy and its selective route, lipophagy, in the turnover of lipid stores in animals, fungi, and plants.

Improvement of a continuous ethanol fermentation from sweet sorghum stem juice using a cell recycling system

The process variables (aeration rate and recycle ratio) of a continuous ethanol fermentation with a cell recycling system (CRS) by Saccharomyces cerevisiae NP 01 from sweet sorghum stem juice were optimized using response surface methodology (RSM). The relationship between intracellular composition and fermentation efficiency was also investigated. RSM results revealed that the optimum aeration rate and recycle ratio were 0.25vvm and 0.625, respectively. The validation experiment under the optimum conditions indicated high precision and reliability of the experiment, achieving an actual ethanol concentration (PE) of 99.28g/l, which was very close to the predicted value (98.01g/l), and a very high ethanol productivity (QP) of 7.94g/lh. The intracellular composition of the yeast cells (i.e., unsaturated fatty acids (UFAs), total fatty acids (TFAs), ergosterol and trehalose) was positively related to the fermentation efficiency and yeast adaptive response under ethanol stress. A higher ratio of UFAs/TFAs and ergosterol strongly promoted yeast viability and ethanol fermentation. Additionally, high trehalose content was observed when the yeast was subjected to stress conditions.

Variation of fermentation redox potential during cell-recycling continuous ethanol operation

Fermentation redox potential was monitored during cell-recycling continuous ethanol operation. The cell-recycling system (CRS) was operated using two hollow fibre (HF) membranes (pore sizes 0.20 and 0.65μm) at three dilution rates (0.02, 0.04 and 0.08h−1). Saccharomyces cerevisiae NP 01 were recycled in the fermenter at a recycle ratio of 0.625. Aeration was provided at 2.5vvm for the first 4h and then further supplied continuously at 0.25vvm. As steady state was established, results showed that the fermentation redox potential was lower for processes employing CRS than those without. At the same dilution rates, the sugar utilization and ethanol production with CRS were higher than those without CRS. The highest fermentation efficiency (87.94g/l of ethanol, ∼90% of theoretical yield) was achieved using a 0.2-μm HF membrane CRS at a dilution rate of 0.02h−1. It was found that 7.53–10.07% of the carbon derived from glucose was incorporated into the yeast. Further, at the same dilution rates, yeast in the processes with CRS incorporated less carbon into ethanol than in those grown without CRS. This result suggests that processes involving CRS utilize more carbon for metabolite synthesis than biomass formation. This indicated that the processes with CRS could utilize more carbon for metabolite synthesis than biomass formation.

Significant roles of the (pro)renin receptor in integrity of vascular smooth muscle cells

The (pro)renin receptor ((P)RR) is known to play an important role in the pathogenesis of vascular complications in diabetes mellitus and hypertension through its function in activating the local renin-angiotensin system. Recent studies have shown that the (P)RR is an accessory protein of the vacuolar H(+)-ATPase, suggesting a more fundamental and developmental function. In this study, smooth muscle cell-specific (P)RR/Atp6ap2 conditional knockout mice were generated. Smooth muscle cell-specific ablation of the (P)RR resulted in nonatherogenic sclerosis in the abdominal aorta. The deletion of the (P)RR did not affect ambulatory blood pressure levels. In cultured murine vascular smooth muscle cells (VSMCs), ablation of the (P)RR suppressed the expression of the Vo subunit c of the vacuolar H(+)-ATPase and impaired the cell recycling system, leading to autophagic cell death. In addition, loss of the (P)RR in VSMCs induced the expression of monocyte chemotactic protein-1 and interleukin-6 mRNAs. These results suggest that the (P)RR is essential for cell survival and downregulation of vascular inflammation in murine VSMCs through maintaining normal function of the vacuolar H(+)-ATPase.

Recovery of residual soluble protein by two-step precipitation process with concomitant COD reduction from the yeast-cultivated cheese whey

The present study was conducted to recover the residual soluble protein after cultivation of yeast (K. marxianus) in cheese whey. Cheese whey continuous fermentation with cell recycle system was carried out at 40°C and pH 3.5. The yeast biomass was separated from the fermented broth by centrifugation and residual soluble protein from fermented whey supernatant was precipitated by heat treatment (at 100°C, pH 4.5 and 10min incubation). The maximum soluble protein recovery up to 53% was achieved at pH 4.5 with 54% residual COD removal. However, gravity sedimentable precipitates were obtained at pH 3.5 with 47% protein recovery. Therefore, the reactor (scale up) study was conducted at pH 3.5 with agitation, which resulted in 68% of residual soluble protein recovery and simultaneously residual COD removal of 62%. Further precipitation/coagulation of soluble protein was also evaluated using carboxymethylcellulose (CMC) and then two precipitation (thermal followed by CMC precipitation) processes were combined to increase the protein precipitation, which finally reached up to 81% of total soluble protein recovery from the supernatant. This optimized process could be applied to recover the residual protein left after fermentation of cheese whey without centrifugation.

Enhanced ethanol production by continuous fermentation in a two-tank system with cell recycling

An experimental method for producing ethanol continuously was designed and tested with a cell-recycling two-tank system, which was composed of two fermentors, each of which was individually equipped with a settler for recycling flocculent yeast. This system was effective for the continuous fermentation of ethanol from sucrose at high cell-recycling (r=0.8–0.9) and dilution (up to 0.48h−1) rates. The system has several advantages; the high cell concentration in the fermentors and relief of substrate and product inhibition. Thus, the enhanced productivity using this continuous fermentation with the two-tank cell-recycling system was significantly higher compared with that of the batch fermentation. The results indicate that increased recycling ratios caused an increase in biomass concentration and subsequently, product concentration in the tank. The ethanol productivity increased with the dilution rate, but higher dilution rates could render increasing amounts of sugar unconverted. Continuous fermentation with the sugar feed concentration of 160g/l at r=0.9 and dilution rate of 0.2h−1 achieved the highest productivity with less than 2% of the unconverted sugar in the product steam. Under the same cell recycling ratios a productivity range of 6.9–7.5g/lh−1 could be achieved with feeding concentrations of 80–200g/l, while batch fermentation at these sugar concentrations led to productivities of 3.85–4.48g/lh−1.

Glutathione production using magnetic fields generated by magnets

The objective of this work was to study the production of GSH by Saccharomyces cerevisiae ATCC 7754 in a fermentor (5 L) using a cell recycle system with magnets. The fermentation conditions were 20°C, 500 rpm, 5% (v/v) of inoculum, pHinitial 5, 1.1 vvm aeration and total fermentation time of 72 h. The time of application of MF ranged from 24, 48 or 72 h. In comparison to the control experiment, the best results were obtained with 72 h of application of MF. The cell concentration reached 19.5 g/L and GSH concentration was 271.9 mg/L that corresponded to an increase of 2.63 and 32.1% compared to the control experiment, respectively.

Continuous butanol fermentation from xylose with high cell density by cell recycling system

A continuous butanol production system with high-density Clostridium saccharoperbutylacetonicum N1-4 generated by cell recycling was established to examine the characteristics of butanol fermentation from xylose. In continuous culture without cell recycling, cell washout was avoided by maintaining pH>5.6 at a dilution rate of 0.26h−1, indicating pH control was critical to this experiment. Subsequently, continuous culture with cell recycling increased cell concentration to 17.4gL−1, which increased butanol productivity to 1.20gL−1h−1 at a dilution rate of 0.26h−1 from 0.529gL−1h−1 without cell recycling. The effect of dilution rates on butanol production was also investigated in continuous culture with cell recycling. Maximum butanol productivity (3.32gL−1h−1) was observed at a dilution rate of 0.78h−1, approximately 6-fold higher than observed in continuous culture without cell recycling (0.529gL−1h−1).

Continuous microbial fuel cell using a photoautotrophic cathode and a fermentative anode

AbstractA complete microbial fuel cell (MFC) operating under continuous flow conditions and using Chlorella vulgaris at the cathode and Saccharomyces cerevisiae at the anode was investigated for the production of electricity. The MFC was loaded with different resistances to characterise its power capabilities and voltage dynamics. A cell recycle system was also introduced to the cathode to observe the effect of microalgae cell density on steady‐state power production and dynamic voltage profiles. At the maximum microalgae cell density of 2140 mg/L, a maximum power level of 0.6 mW/m2 of electrode surface area was achieved. The voltage difference between the cathode and anode decreased as the resistance decreased within the closed circuit, with a maximum open circuit voltage (infinite resistance) of 220 mV. The highest current flow of 1.0 mA/m2 of electrode surface area was achieved at an applied resistance of 250 Ω.

Continuous Production of Succinic Acid Using an External Membrane Cell Recycle System

Succinic acid was produced by continuous fermentation of Actinobacillus succinogenes sp. 130Z in an external membrane cell recycle reactor to improve viable cell concentration and productivity. Using this system, cell concentration increased to 16.4 g/l at the dilution rate 0.2 h-1, up to 3 times higher than that of batch culture, and the volumetric productivity of succinic acid increased up to 6.63 g/l/h at the dilution rate 0.5 h-1, 5 times higher than that of batch fermentation. However, in the continuous culture using a high dilution rate, operational problems including severe membrane fouling and contamination by lactic acid producer were observed. Another succinic acid producer, Mannheimia succiniciproducens MBEL55E, was also utilized in this system, and the cell concentration and productivity of succinic acid at the dilution rate of 0.3 h-1 were found to be above 3 and 2.3 times higher, respectively, compared with those obtained at the dilution rate of 0.1 h-1. These observations give a deep insight into the process design for a continuous succinic acid production by microorganisms.