Kinetic model of cell growth and secondary metabolite synthesis in plant cell culture ofThalictrum rugosum

A structured kinetic model was proposed to describe cell growth and synthesis of a secondary metabolite, berberine, in batch suspension culture ofThalictrum rugosum. The model was developed by representing the physiological state of the cell in terms of the activity and the viability, which can be estimated using the culture fluorescence measurement. In the proposed model, the cells were divided into three types; active-viable, nonactive-viable, and dead cells. The model was formulated in terms of cell growth (dry/fresh weight, activity, and viability), carbon source utilization (sucrose, glucose and fructose), and product formation (intracellular and extracellular berberine). The concept of cell expansion and the death phase were also included in this model to describe the sugar accumulation and the release of intracellular berberine into medium by cell lysis, respectively. The parameters used in this model were estimated based on the experimental results in conjunction with numerical optimization techniques. Satisfactory agreement between the model and experimental data was obtained. The proposed model could accurately predict cell growth and product synthesis as well as the distribution of the secondary metabolite between the cell and the medium. It is suggested that the proposed model could be extended as a useful framework for quantitative analysis of physiological characteristics in the other plant cell culture systems.     

植物细胞生物反应器培养的研究进展(I)

利用植物细胞大规模悬浮培养生产植物有用代谢产物在近些年来取得了很大发展,但植物细胞悬浮培养的工业化应用受到来自生物及工程技术上的限制.本文针对植物细胞培养的基本特点,详细讨论了与大规模生产有关的工程技术方面的问题,如植物细胞聚集、溶氧及气体成分、流体性能、剪切力对植物细胞培养产生的影响.     

植物细胞生物反应器培养的研究进展(I)

利用植物细胞大规模悬浮培养生产植物有用代谢产物在近些年来取得了很大发展,但植物细胞悬浮培养的工业化应用受到来自生物及工程技术上的限制。本文针对植物细胞培养的基本特点,详细讨论了与大规模生产有关的工程技术方面的问题,如植物细胞聚集、溶氧及气体成分、流体性能、剪切力对植物细胞培养产生的影响。     

Growth and biosynthetic characteristics of ginseng (Panax japonicus var. repens) deep-tank cell culture in bioreactors

The aim of the work was to study the growth characteristics of cultured cells of Panax japonicus var. repens, an endemic plant of the Primorski Krai of Russia, grown in laboratory bioreactors and to determine the content of basic ginsenosides under these conditions. An increase of the inoculum size of the culture produced higher biomass accumulation and economic coefficient but slightly reduced the specific growth rate. An increase in the auxin concentration in a medium by adding 2,4-D practically did not affect growth characteristics of the culture but significantly reduced the size of cell aggregates. In all treatments tested, all major ginsenosides (Rb₁, Rc, Rb₂, Rd, Rf, Rg₁, and Re) were found in the culture. The total ginsenoside content was 2–3% per biomass dry weight. Meantime, ginsenosides of the Rg-series with protopanaxatriol as aglycone prevailed (70% of the total ginsenoside content). The culture conditions considerably affected the ratio of individual ginsenosides. In 2,4-D-containing medium, the preferential synthesis of Re ginsenoside was observed while both Rg₁ and Re were synthesized in other treatments.     

A population balance equation model of aggregation dynamics in Taxus suspension cell cultures

The nature of plant cells to grow as multicellular aggregates in suspension culture has profound effects on bioprocess performance. Recent advances in the measurement of plant cell aggregate size allow for routine process monitoring of this property. We have exploited this capability to develop a conceptual model to describe changes in the aggregate size distribution that are observed over the course of a Taxus cell suspension batch culture. We utilized the population balance equation framework to describe plant cell aggregates as a particulate system, accounting for the relevant phenomenological processes underlying aggregation, such as growth and breakage. We compared model predictions to experimental data to select appropriate kernel functions, and found that larger aggregates had a higher breakage rate, biomass was partitioned asymmetrically following a breakage event, and aggregates grew exponentially. Our model was then validated against several datasets with different initial aggregate size distributions and was able to quantitatively predict changes in total biomass and mean aggregate size, as well as actual size distributions. We proposed a breakage mechanism where a fraction of biomass was lost upon each breakage event, and demonstrated that even though smaller aggregates have been shown to produce more paclitaxel, an optimum breakage rate was predicted for maximum paclitaxel accumulation. We believe this is the first model to use a segregated, corpuscular approach to describe changes in the size distribution of plant cell aggregates, and represents an important first step in the design of rational strategies to control aggregation and optimize process performance.     

Improvement of biomass and juvenile hormone III (JH III) production from <Emphasis Type="Italic">Cyperus aromaticus</Emphasis> cell suspension culture via in situ membrane filtration technology

The incorporation of membrane filtration technology in plant cell suspension culture was to facilitate in situ medium exchange as well as to eliminate possible introduction of contaminant in the process. The study had been carried out in Cyperus aromaticus cell suspension culture, which is known to produce a bioinsecticide known as juvenile hormone III (JH III). The effect of different volume and flow rate of replenishment toward cell biomass and JH III production were studied. The experimental finding indicates that the flow rate of medium replenishment ranging from 1 to 6 ml min⁻¹ did not affect the cellular structure and morphology the cells. Medium replenishment of 75 v/v% through the membrane system leads to higher cell biomass and metabolite production which correlates to a value as high as 64 and 112%, respectively. The reduction in doubling time, extended exponential growth and increment in specific growth rate were also demonstrated. A 50 v/v% medium replenishment with membrane filtration system was identified to be an economical and feasible application for the production of JH III metabolite at a large scale. The results obtained showed the potential of in situ membrane filtration system for the enhancement of cell biomass and metabolite yield in plant cell culture.     

Establishment of callus and cell suspension cultures from Gypsophila paniculata leaf segments and study of the attachment of host cells by Erwinia herbicola pv. gypsophilae

Callus and cell suspension cultures were initiated from leaf segments of G. paniculata. Fresh and dry weights measurements of callus showed that callus growth was optimal on MS medium supplemented with 1.0 mg l^–1 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.2 mg l^–1 benzyladenin (BA). Calli cultured on this medium, showed a two-fold increase in fresh weight by the fourth week of incubation. The initiated hard green callus was repeatedly subcultured on MS medium containing increasing concentrations of 2,4-D in order to increase its friability. The friable callus was then used for establishment of a cell suspension culture. Maximum growth of the suspension culture was on medium supplemented with 1.0 mg l^–1 2,4-D and 0.2 mg l^–1 BA.The suspension culture was used for studying plant host attachment in both electron and light microscopy. Upon infection with E. herbicola, plant cells showed aggregate formation within 24 h of infection. In the presence of the pathogenic Ehg,the number of aggregates formed was 342 aggregates ml^–1, in the presence of the non-pathogenic Ehg154 aggregates ml^–1 and in the control 115 aggregates ml^–1. These results show that the pathogenic strain causes formation of cell aggregates 5.8 times greater than the non-pathogenic one. Based on these results, it can be hypothesized that bacterial cells of the pathogenic strains bind to the plant cells and may form a bridge for attachment of plant cells to one another. Observations by electron microscope show that bacterial cells do attach to plant cells and that this attachment might be via formation of a bridge between the bacteria and the plant cell.     

Problems of optimisation of plant cell culture processes.

The adoption of plant cell cultures as an industrial process depends greatly on the economics of such a process. The multicycle or draw-fill culture technique is one method for improving the productivity and, hence, cost of a process. Mathematical models have been devised for the functional relationships between the nominal costs of biomass and secondary metabolites and the plant cell growth characteristics in a multicycle growth system. The models were used to evaluate the data obtained with cultures of Dioscorea deltoidea (which produces diosgenin) and Panax ginseng, grown in various types of bioreactors. The multicycle system gave an increase of 1.5-2 in biomass productivity compared with batch culture, but was probably only commercially viable if the cost of the process in the bioreactor was at least 30 times that of the medium and if an inoculum of about 30% of the culture of the previous cycle was left in the bioreactor. In the multicycle system incompletely utilised nutrient or metabolite accumulation can only reach 1.43 times or less that of the initial values. With the P. ginseng culture, about 75% of the calculated maximum cell packing density per fresh weight (approximately 530 g 1-1) in this regime was achieved. The possibility of growth in the standard bioreactor of a shear sensitive type culture was shown with a marine impeller speed up to 330 cm s-1.     

Morphohistological study of the different constituents of a banana (Musa AAA, cv. Grande naine) embryogenic cell suspension

Five types of cellular aggregates have been characterised in embryogenic cell suspensions of banana (Musa AAA Grande naine cv.). Type I corresponded to isolated cells or to small cell aggregates. Type II were composed of embryogenic cells. Type III can be distinguished from type II due to the presence of peripheral proliferation zones with embryonic cells. Type IV were composed of protodermic masses histologically comparable to proembryos. Type V were nodules composed of a central zone of meristematic cells and of an external zone of starchy cells. Each culture flask of a cell line contained a majority of one of the above-mentioned aggregate types. Histological studies of somatic embryo developement on semi-solid regeneration medium showed that there were close similarities between the initial steps of ontogenesis of the embryos and the different cell aggregates in liquid multiplication medium. It appeared that aggregates II–IV of the suspension belong to the same development continuum which reproduces the initial phases of somatic embryo ontogenesis on semi-solid medium. Type V resulted from the development of type IV, for which ontogenesis is hindered by direct contact with 2,4-dichlorophenoxyacetic acid and the shaken liquid multiplication medium. Type I aggregates probably do not belong to the development continuum but rather correspond to the degeneration of the other types of aggregates in the suspension. The presence of intermediate types in the liquid medium reinforces the hypothesis of a relationship between the aggregates. The aggregates tended to develop through time from a majority of type II or III at the beginning of their culture to types IV–V for older suspensions. Received: 10 August 1999 / Revision received: 8 November 1999 / Accepted: 9 November 1999     

Callus formation and induction of a cell suspension culture from Acacia senegal

Cell proliferation has been induced from the cambial zone of a branch of Acacia senegal, kept on the basal Knop and Ball medium in the presence of auxin. Transferred on the more complete nutrient medium of Schenk and Hildebrandt, the colonies gave rise to several cell lines. One of the friable lines, consisting of aggregates of parenchymatous cells, gave a cell suspension culture in an agitated liquid medium which is maintained as a strain of illimited growth. The heterogeneous suspension did not undergo noticeable changes after eight transfers. Aggregates collected on a 1000-m nylon seive were able to grow on a solid medium and gave back a friable callus similar to the initial colonies.     

A systems approach to plant bioprocess optimization

A dynamic model for plant cell metabolism was used as a basis for a rational analysis of plant production potential in in vitro cultures. The model was calibrated with data from 3-L bioreactor cultures. A dynamic sensitivity analysis framework was developed to analyse the response curves of secondary metabolite production to metabolic and medium perturbations. Simulation results suggest that a straightforward engineering of cell metabolism or medium composition might only have a limited effect on productivity. To circumvent the problem of the dynamic allocation of resources between growth and production pathways, the sensitivity analysis framework was used to assess the effect of stabilizing intracellular nutrient concentrations. Simulations showed that a stabilization of intracellular glucose and nitrogen reserves could lead to a 116% increase in the specific production of secondary metabolites compared with standard culture protocol. This culture strategy was implemented experimentally using a perfusion bioreactor. To stabilize intracellular concentrations, adaptive medium feeding was performed using model mass balances and estimations. This allowed for a completely automated culture, with controlled conditions and pre-defined decision making algorithm. The proposed culture strategy leads to a 73% increase in specific production and a 129% increase in total production, as compared with a standard batch culture protocol. The sensitivity analysis on a mathematical model of plant metabolism thus allowed producing new insights on the links between intracellular nutritional management and cell productivity. The experimental implementation was also a significant improvement on current plant bioprocess strategies.     

Analysis of pigmentation in individual cultured plant cells using an image processing system

Anthocyanin accumulation in strawberry (Fragaria ananassa) cells cultured on a solid medium was monitored using an image-processing system that did not require direct sampling or destruction of the cells. Because of the intercellular heterogeneity of secondary metabolite production in plant cell cultures, the maximum metabolite concentration in individual cells is often more than 10 times higher than that of the average concentration. An image-processing based method enabled the growth and the pigmentation behavior of individual cells to be traced. Changes in the time courses of the anthocyanin content of individual cells differed from each other, although the average anthocyanin contents increased gradually with time in a batch culture. However, these various changing patterns in the anthocyanin content of each cell were independent of the cell cycle. In addition, image analysis revealed that the two cells just after cell division were almost identical to each other both in size and anthocyanin content. The proposed method which uses an image-processing system provides a useful tool for analyzing the secondary metabolism in individual cultured plant cells.     

Pulsed electric field stimulates plant secondary metabolism in suspension cultures of Taxus chinensis

The effects of pulsed electric field (PEF) on growth and secondary metabolite production by plant cell culture were investigated by using suspension cultures of Taxus chinensis as a model system. Cultured cells in different growth phases were exposed to a PEF (50 Hz, 10 V/m) for various periods of time. A significant increase in intracellular accumulation of taxuyunnanine C (Tc), a bioactive secondary metabolite, was observed by exposing the cells in the early exponential growth phase to a 30-min PEF. The Tc content (i.e., the specific production based on dry cell weight) was increased by 30% after exposure to PEF, without loss of biomass, compared with the control. The combination of PEF treatment and sucrose feeding proved useful for improving secondary metabolite formation. Production levels of reactive oxygen species, extracellular Tc, and phenolics were all increased, whereas cell capacitance was decreased with PEF treatment. The results show that PEF induced a defense response of plant cells and may have altered the cell/membrane's dielectric properties. PEF, an external stimulus or stress, is proposed as a promising new abiotic elicitor for stimulating secondary metabolite biosynthesis in plant cell cultures.     

Behavior of cell aggregate of Carthamus tinctorius L. cultured cells and correlation with red pigment formation

The formation processes of Carthamus tinctorius cell aggregates in a growth medium and the correlation of red pigment formation with cell aggregate sizes were investigated. About 80% of cell aggregates in the growth medium were > 1.00 mm in size. The growth rate of large cell aggregates was more rapid than that of small cell aggregates. Most cell aggregates > 0.50 mm in size became larger or smaller than their original sizes during the culture. A high level of red pigment formation was observed when cell aggregates obtained by the preculture using cell aggregates < 1.00 mm in size were cultured in the production medium.     

Long-term culture of rat liver cell spheroids in hormonally defined media

Liver cells of new-born rats, which were found to be able to form spheroidal aggregates when cultured on a nonadherent plastic substratum, were studied under various conditions of culture, mainly by adding different nutrients and growth factors to the culture medium. Analysis of hepatocyte-specific functions was carried out by immunoprecipitation to detect specific proteins newly secreted by liver cell spheroids on different days of culture. When no supplement was added to culture medium, the secretion of albumin and transferrin by liver cell spheroids was no longer detectable after 2 weeks of culture. When dexamethasone, glucagon, insulin, and EGF were added to culture medium, the secretion of albumin and transferrin remained detectable at least until 60 days of culture. This was even more striking when trace elements were added in addition to the three hormones and EGF. The effects of addition of these various factors to culture medium were also detectable with respect to alpha-FP secretion. Even after 54 days of culture in total supplemented medium, these liver cell spheroids could be transferred on a collagen-coated plastic substratum to form a monolayer of uniform liver parenchyma-like cells. The presence of extracellular matrix-like material was observed on the surface of cell spheroids. This could be responsible for attachment and fusion between cell spheroids. Thus, liver cell spheroids cultured in total supplemented medium ensured cell attachment to a biological matrix and cell-cell contact, which is thought to help maintain cell differentiation. Liver cell spheroids offer the possibility of toxicological and pharmacological studies as well as cultures in biomatrix and coculture systems. In addition these liver cells can be used for experiments in liver cell transplantation.     

Biomass segregation in sage cell suspension culture

The biomass of sage (Salvia officinalis L.) cell suspension culture was composed of single cells and cell aggregates. The development of aggregated cell culture from a single-cell suspension was monitored by particle size distribution for four particle size classes. Particle size distribution was compared between the biomass grown in bioreactor and shake flasks. The size of the particles had a strong influence on content of secondary metabolite, ursolic acid (UA). The single cell biomass fraction accumulated up to 7.7 mg UA g^–1 DW which was up to 50 times higher compared to aggregated biomass fractions.     

On spontaneous mutagenesis and cell cultivation conditions.

The leu2 revertant content of a Saccharomyces cerevisiae cell culture increases as the leucine concentration in the nutrient solid medium decreases. Reversions form in the S-phase of the cell cycle. If a cell culture from a medium with a low concentration of leucine containing the revertants which have just formed is transferred on a medium with a normal or higher than normal leucine content, these 'newborn' revertants disappear at the end of the G1-phase or at the beginning of the S-phase of the next cell cycle. These data can be explained either by a difference in the ability of revertants formed in the culture to compete with the cells of the initial strain on different media, or on the basis of the intermediate heteroduplex model proposed by F.W. Stahl (1988).     

Arabinogalactan proteins are involved in cell aggregation of cell suspension cultures of <Emphasis Type="Italic">Beta vulgaris</Emphasis> L.

Arabinogalactan proteins (AGPs) are glycoproteins present at cell surfaces. Although exact functions of AGPs remain elusive, they are implicated in plant growth and development. The aim of this study was to evaluate the role of AGPs in the process of cell aggregation of Beta vulgaris L. suspension cultures. It was observed that B. vulgaris suspension cultures accumulated AGPs in parallel form to its cell growth. The AGPs maximum content in the stationary phase was 0.330 mg g⁻¹ dry weight (DW) in the cell wall (CW) and 1.534 mg g⁻¹ DW in the culture medium (CM), generating cell aggregates >500 μm (93.21% DW). The addition of tunicamycin (TM) caused a reduction of AGPs content in CW and CM of 46 and 64%, respectively. These changes were associated with inhibition of growth and the reduction of the cell aggregates >500 μm (50.0% DW). When TM was removed from the CM, cell growth, aggregation, and AGPs content on CW and CM were recovered. Precipitation of AGPs with Yariv reagent generated a reduction of 61.14% of AGPs content in CW and a total inhibition of AGPs secretion in CM. This Yariv treatment generated a reduction in the cell aggregates >500 μm of 51.31% of DW. When the Yariv reagent was removed from the culture, cells did not recover their AGPs accumulation. In addition, cell cultures did not recover their ability to grow and aggregate. These results indicate that AGPs are molecules required in the cellular aggregation process of B. vulgaris L. suspension cultures.     

Strategies for enhancing monoclonal antibody accumulation in plant cell and organ cultures.

Various strategies aimed at improving IgG(1) antibody accumulation in transgenic tobacco cell and organ cultures were tested. The form of tissue had a significant effect on antibody levels; shooty teratomas were less productive than hairy roots or suspended cells. Although there were several disadvantages associated with hairy roots compared with suspensions, such as slower growth, slower antibody production, and formation of a greater number of antibody fragments, the roots exhibited superior long-term culture stability. Antibody accumulation in hairy root cultures was improved by increasing the dissolved oxygen tension to 150% air saturation, indicating the need for effective oxygen transfer in root reactors used for antibody production. Preventing N-linked glycosylation using tunicamycin or inhibition of subsequent glycan processing by castanospermine reduced antibody accumulation in the biomass and/or medium in cell suspensions. Loss of antibody from the cultures after its secretion and release into the medium was identified as a major problem. This effect was minimized by inhibiting protein transport in the secretory pathway using Brefeldin A, resulting in antibody accumulation levels up to 2.7 times those in untreated cells. Strategies for protecting secreted antibody, such as addition of poly(vinylpyrrolidone) and periodic harvesting from the medium using hydroxyapatite resin, also increased antibody titers. The mechanisms responsible for the disappearance of antibody from plant culture media were not clearly identified; degradation by proteases and conformational modification of the antibody, such as formation of aggregates, provided an explanation for some but not all the phenomena observed. This work demonstrates that the manipulation and control of culture conditions and metabolic processes in plant tissue cultures can be used to improve the production of foreign proteins. However, loss of secreted antibody from plant culture medium is a significant problem that may limit the feasibility of using product recovery from the medium to reduce downstream processing costs relative to agricultural systems.     

Modeling kinetics of a large‐scale fed‐batch CHO cell culture by Markov chain Monte Carlo method

Markov chain Monte Carlo (MCMC) method was applied to model kinetics of a fed‐batch Chinese hamster ovary cell culture process in 5,000‐L bioreactors. The kinetic model consists of six differential equations, which describe dynamics of viable cell density and concentrations of glucose, glutamine, ammonia, lactate, and the antibody fusion protein B1 (B1). The kinetic model has 18 parameters, six of which were calculated from the cell culture data, whereas the other 12 were estimated from a training data set that comprised of seven cell culture runs using a MCMC method. The model was confirmed in two validation data sets that represented a perturbation of the cell culture condition. The agreement between the predicted and measured values of both validation data sets may indicate high reliability of the model estimates. The kinetic model uniquely incorporated the ammonia removal and the exponential function of B1 protein concentration. The model indicated that ammonia and lactate play critical roles in cell growth and that low concentrations of glucose (0.17 mM) and glutamine (0.09 mM) in the cell culture medium may help reduce ammonia and lactate production. The model demonstrated that 83% of the glucose consumed was used for cell maintenance during the late phase of the cell cultures, whereas the maintenance coefficient for glutamine was negligible. Finally, the kinetic model suggests that it is critical for B1 production to sustain a high number of viable cells. The MCMC methodology may be a useful tool for modeling kinetics of a fed‐batch mammalian cell culture process. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010