Cell Growth In Batch Cultures Research Articles

Whey and post-frying oil as substrates in the process of microbial lipids obtaining: a value-added product with nutritional benefits

AbstractYarrowia lipolytica has found many biotechnological applications. The species has a number of regulatory mechanisms to maintain cellular homeostasis, enabling biomass growth in complex media. The aim of this study was to evaluate the use of Y. lipolytica yeast as a platform for the simultaneous management of several industrial by-products and the production of microbial lipids with application potential in the chemical and food industries. Batch cultures of KKP 379 strain were conducted in media with post-frying rapeseed oil (PFO) and a by-product of curd cheese production—acid whey. To evaluate the potential of Yarrowia as a nutraceutical, quantitative and qualitative analyses of microbial sterols were carried out along with an assessment of the biomass mineral composition. It was indicated that the composition and content of sterols varied depending on the phase of cell growth in batch culture. During culture in medium with 20% (v/v) whey and 50 g/L PFO, the cellular lipid content reached 39% (w/w). The highest amount of sterols per dry biomass (7.38 mg/g) and cellular lipids (21.08 mg/g) was recorded after 38 h of culture. The dominant was ergosterol 12.10 mg/g (57%). In addition, the composition of carbon and nitrogen sources in the medium affected the content of selected elements in biomass, indicating that substrate modification can be a tool for manipulating the composition of yeast cells. The results of the study showed that the selection of waste substrates is an important factor in regulation of the cellular lipid accumulation efficiency, as well as the content of certain sterols.

Continuous culture techniques as simulators for standard cells: Jacques Monod's, Aron Novick's and Leo Szilard's quantitative approach to microbiology.

Continuous culture techniques were developed in the early twentieth century to replace cumbersome studies of cell growth in batch cultures. In contrast to batch cultures, they constituted an open concept, as cells are forced to proliferate by adding new medium while cell suspension is constantly removed. During the 1940s and 1950s new devices have been designed-called "automatic syringe mechanism," "turbidostat," "chemostat," "bactogen," and "microbial auxanometer"-which allowed increasingly accurate quantitative measurements of bacterial growth. With these devices cell growth came under the external control of the experimenters and thus accessible for developing a mathematical theory of growth kinetics-developed mainly by Jacques Monod, Aron Novick and Leo Szilard in the early 1950s and still in use today. The paper explores the development of continuous culture devices and claims that these devices are simulators for standard cells following specific requirements, in particular involving mathematical constraints in the design and setting of the devices as well as experiments. These requirements have led to contemporary designs of continuous culture techniques realizing a specific event-based flow algorithm able to simulate directed evolution and produce artificial cells and microorganisms. This current development is seen as an alternative approach to today's synthetic biology.

Modeling and parameter identification for a nonlinear multi-stage system for dha regulon in batch culture

The bioconversion of glycerol to 1,3-propanediol (1,3-PD) is a complex bioprocess. In this paper, based on biological phenomena of different characteristics at different stages and the genetic regulation of dha regulon, we consider a fourteen-dimensional nonlinear multi-stage dynamic system with unknown time and system parameters for formulating the multi-stage cell growth in batch culture. Some important properties of the multi-stage system are discussed. Our goal is to identify the time and system parameters. To this end, we present a parameter identification problem in which the time and system parameters are decision variables and the cost function measures the discrepancy between experimental data and computational results, subject to the multi-stage system, parameter constraints and continuous state inequality constraints. The system sensitivity (the cost function’s gradient, namely, the derivative of the cost function with respect to the time and system parameters), which can be computed by solving an auxiliary initial value problem, can be regarded as the search direction of optimization algorithm. The identification problem is converted into a sequence of nonlinear programming subproblems through the application of the time-scaling transformation, the constraint transcription and local smoothing approximate techniques. Due to the highly complex nature of the identification problem, the computational cost is high. Thus, a parallel algorithm is proposed to solve these subproblems based on the novel combinations of system sensitivity and genetic algorithm. Finally, numerical results show that the multi-stage system can reasonably describe the process of batch culture.

An improved model for multistage simulation of glycerol fermentation in batch culture and its parameter identification

The bioconversion of glycerol to 1,3-propanediol is a complex bioprocess. In this study, we aim to explore a novel model for describing the multistage cell growth in batch culture. This is achieved by a modification at the specific rate of cell growth in consideration of its time-dependent changes. The existence, uniqueness and boundedness of solutions to the system and the continuity of solutions with respect to the parameters are discussed. In addition, a parameter identification problem of the system is developed and a feasible optimization algorithm is constructed to solve it. Numerical result shows that the improved model could describe the batch culture well.

Kinetic analysis of the effect of cell density on hybridoma cell growth in batch culture

The effect of cell density on cell growth was investigated in a suspension batch culture of hybridoma cells. The specific growth rate was found to increase with increasing initial cell density and then to decrease with further increases in initial cell density. In order to quantitatively describe the dependence of specific growth rate on cell density, a kinetic model is proposed, which satisfactorily represents the experimental data.

Modeling of typical microbial cell growth in batch culture

A mathematical model was developed, based on the time dependent changes of the specific growth rate, for prediction of the typical microbial cell growth in batch cultures. This model could predict both the lag growth phase and the stationary growth phase of batch cultures, and it was tested with the batch growth of Trichoderma reesei and Lactobacillus delbrueckii. Modeling and simulation of microbial cell growth is important both theoretically and practically. Although the Monod model (1) has been the most widely used for the prediction of cell growth, it only fits the exponen- tial growth phase of the growth, without any inhibi- tion. The lag growth phase, decreased growth phase and the stationary growth phase of a typical microbial batch culture growth curve can not be predicted using the Monod model. The typical growth curve of batch culture is the result of continuous changes of the spe- cific growth rate, µ, with culture time. Although many efforts have been made to expand the Monod model in order to predict the typical microbial growth curve of batch culture, the time dependent changes of µ were often neglected in prediction of the lag growth phase. Efforts made to predict the lag growth phase simply defined the lag time in terms of cell growth, t L (2,3). The lag growth phase was related with the changes of µ and defined in the following way (3):

Modeling retrovirus production for gene therapy. 1. Determination Of optimal bioreaction mode and harvest strategy.

Although retroviruses are a promising tool for gene therapy, there are two major problems limiting the establishment of viable industrial processes: retrovirus stability and low final yield in the supernatant. This fact emphasizes the need for an effective process optimization, not only at a genetic level but also at a bioprocess engineering level. In part 1 of this paper a mathematical model was developed to optimize the bioreaction yield by determining the best retrovirus harvest strategy in perfusion cultures. PA317 cells producing recombinant retroviruses were used to develop and test this model. Cell culture was performed in stirred tanks using porous supports. The parameters of the proposed model were experimentally determined for batch and perfusion cultures at 32 and 37 degrees C both with and without additives to enhance production; the model was then validated. This model allowed the determination of the optimal values of all operational variables included: batch and perfusion duration and perfusion rate. The highest productivity (2682 virus cm(-)(3) h(-)(1)) was obtained under the following conditions: batch at 37 degrees C for 53 h followed by perfusion at 32 degrees C for 23 h with a perfusion rate of 0.107 h(-)(1). This value was 3.5-fold higher than the best result obtained in batch cultures for the same conditions of titer and quality. A sensitivity analysis of the parameters showed that the parameters that affect most the final productivity depend on the bioreaction phase: cell growth in batch culture and production and product degradation in perfusion culture. In part 2 of this paper, this model is extended to the first step of downstream processing, and the addition of further steps to the process is discussed in order to achieve global process optimization.

Cultivation of the hyperthermophilic archaeonSulfolobus solfataricus in low-salt media

Two low-salt complex media, bactopeptone and desalted yeast extract, were used for high density cultivation of the hyperthermophilic archaeonSulfolobus solfataricus (DSM 1617). Bactopeptone, which has low mineral ion content among various complex media, was good for cell growth in batch cultures; the maximal cell density in bactopeptone was comparable to that in yeast extract. Howver, cell growth was rather poor when bactopeptone was added by the fed-batch procedure. Since several vitamins are deficient in bactopeptone, the effect of vitamins on cell growth was examined. Among the vitamins tested, pyridoxine was found to improve the growth rate ofS. solfataricus. To reduce the growth inhibition caused by mineral ions, yeast extract was dialyzed against distilled water and then fed-batch cultures were carried out using a feed medium containing desalted yeast extract. Although the concentrations of mineral ions in yeast extract were significantly lowered by the dialysis procedure, fed-batch cultivation with desalted yeast extract was unsatisfactory. To examine whether low molecular weight solutes in yeast extract are crucial for cell growth, we investigated the effect of trehalose, a most abundant compatible solute in yeast extract, on the growth pattern. Cell densities were increased and the length of the lag phase was markedly shortened by the presence of trehalose, indicating that trehalose plays an important role in the growth ofS. solfataricus.

Effects of yeast extract and glucose on xanthan production and cell growth in batch culture of Xanthomonas campestris

Although available kinetic data provide a useful insight into the effects of medium composition on xanthan production by Xanthomonas campestris, they cannot account for the synergetic effects of carbon (glucose) and nitrogen (yeast extract) substrates on cell growth and xanthan production. In this work, we studied the effects of the glucose/yeast-extract ratio (G/YE) in the medium on cell growth and xanthan production in various operating modes, including batch, two-stage batch, and fed-batch fermentations. In general, both the xanthan yield and specific production rate increased with increasing G/YE in the medium, but the cell yield and specific growth rate decreased as G/YE increased. A two-stage batch fermentation with a G/YE shift from an initial low level (2.5% glucose/0.3% yeast extract) to a high level (5.0% glucose/0.3% yeast extract) at the end of the exponential growth phase was found to be preferable for xanthan production. This two-stage fermentation design both provided fast cell growth and gave a high xanthan yield and xanthan production rate. In contrast, fed-batch fermentation with intermittent additions of glucose to the fermentor during the stationary phase was not favorable for xanthan production because of the relatively low G/YE resulting in low xanthan production rate and yield. It is also important to use a moderately high yeast extract concentration in the medium in order to reach a high cell density before the culture enters the stationary phase. A high cell density is also important to the overall xanthan production rate.

Tetraether type polar lipids increase after logarithmic growth phase of Methanobacterium thermoautotrophicum in compensation for the decrease of diether lipids

The ratios of tetraether to diether type lipids in the total lipid during cell growth in batch cultures of Methanobacterium thermoautotrophicumΔH (DSM 1053) were examined. The proportion of tetraether type lipids to the total lipid was about 80% during the log phase, and at the onset of the transient phase it began to rise up to about 93%. It was kept almost constant at that level throughout the stationary phase. The polar lipid composition changed with the age of the cell culture. The proportions of all the diether type polar lipids were lower and the levels of all tetraether type polar lipids were higher in the stationary phase than in the log phase. On the other hand, the composition of polar head groups, irrespective of the core lipids, was nearly constant in both growth phases measured so far despite the change in core lipid composition.

Tetraether type polar lipids increase after logarithmic growth phase of Methanobacterium thermoautotrophicum in compensation for the decrease of diether lipids

The ratios of tetraether to diether type lipids in the total lipid during cell growth in batch cultures of Methanobacterium thermoautotrophicum ΔH (DSM 1053) were examined. The proportion of tetraether type lipids to the total lipid was about 80% during the log phase, and at the onset of the transient phase it began to rise up to about 93%. It was kept almost constant at that level throughout the stationary phase. The polar lipid composition changed with the age of the cell culture. The proportions of all the diether type polar lipids were lower and the levels of all tetraether type polar lipids were higher in the stationary phase than in the log phase. On the other hand, the composition of polar head groups, irrespective of the core lipids, was nearly constant in both growth phases measured so far despite the change in core lipid composition.

A note on plant cell growth modelling

A model for plant cell growth in batch cultures 1 is reassessed. By simple analysis, it is shown that the predicted oscillatory growth behavior resides mostly with the assumed cell distribution for the inoculum. The substrate consumption equation is shown to imply that cells consume substrate at only a short and well defined interval of the cell cycle. Alternatives to generate the initial synchrony are briefly discussed.

Effect of carbon source and dissolved oxygen level on cell growth and pullulanase production byBacillus stearothermophilus G-82

Cell growth and extracellular pullulanase production ofBacillus stearothermophilus G-82 were investigated in batch culture using a defined medium with glucose, maltose, pullulan or amylopectin as carbon source. Maximum enzyme activity was with pullulan or amylopectin. Cell growth in batch culture was better under oxygen unlimited conditions, while higher total and specific enzyme activities, using pullulan or amylopectin, were obtained in oxygen-limited conditions. Enzyme accumulation took place in the late growth phase. The highest enzyme production of 300 U/I was reached when pullulan was used as carbon source in conditions of oxygen limitation.

Production of 2,3-butanediol by Klebsiella oxytoca

High glucose concentrations result in high levels of 2,3-butanediol, improved yield and productivity, and a decrease in cell growth in batch cultures of Klebsiella oxytoca. A maximum of 84.2 g butanediol/l and a yield of 0.5 was obtained with an initial glucose concentration of 262.6g/l. Adding the substrate in two steps in a modified fed-batch operation resulted in 85.5 g butanediol/l, 6.4 g acetoin/l and 3.4 g ethanol/l with a net yield of 0.5. Increasing the cell density to 60g/l resulted in productivities as high as 3.22 g/l.h.