Accumulation characteristics of biomass and nitrogen and critical nitrogen concentration dilution model of cotton reproductive organ

Several nitrogen (N) field experiments were carried out in Nanjing and Anyang, China, to study the dynamic characteristics of biomass accumulation and N uptake, and to define the dilution curve for critical N concentration in cotton reproductive organ over the growth period. The results show that the total biomass and N accumulation were affected significantly by the rate of N application, exhibiting a sigmoid curve over time. The beginning time of fast N accumulation was 1–5 d earlier than that of biomass accumulation. The cotton lint yield was correlated with N concentration in the reproductive organ and fluctuated with varying N concentration, indicating the existence of luxurious N consumption in the cotton reproductive organ. The N concentration increased with increasing N application rates, and decreased gradually during the growth period. The relationship between biomass and N concentration can be described with a power equation. The patterns of the N concentration dilution model were consistent at both experimental sites, but the model parameter values of a differed. The results presented in this paper indicate that a critical N concentration dilution curve for cotton reproductive organ is independent of ecological region and can be described with a power equation.     

Continuous cultivation of bakers' yeast: Change in cell composition at different dilution rates and effect of heat stress on trehalose level

The cell composition of bakers' yeast in a continuous culture was determined for different dilution rates. Also, the cellular response to heat stress in terms of trehalose, RNA, glycogen and protein was determined at a specified dilution rate of 0.1/h. The amount of storage saccharides, trehalose and glycogen, was found to decrease whereas the amount of RNA and protein increased with increasing dilution rates. As the dilution rate was increased from 0.1 to 0.4/h at 0.05 intervals the steady-state trehalose content decreased from 33 to 8.6 mg/g biomass, and glycogen content from 150 to 93 mg/g biomass. On the other hand, the protein content increased from 420 to 530 mg/g biomass and the RNA content from 93 to 113 mg/g biomass. Heat stress was applied by increasing the medium temperature from 30 to 36, 38 or 40°C at constant dilution rates. The highest amount of trehalose accumulation, 108 mg/g biomass, was achieved when heat stress at 38°C was applied. The protein content, on the other hand, decreased from 350 to 325 mg/g biomass at the end of the experiment.     

Continuous ethanol production by a flocculating strain of Kluyveromyces marxianus: bioreactor performance

A flocculating strain of Kluyveromyces marxianus was used for alcoholic fermentation in a continuous bioreactor working with zero residual concentration in effluent. Specific kinetic parameters were improved by increasing dilution rate, which is similar to results obtained with ultrafiltration systems. Specific biomass accumulation rate had always a value greater than 92.5% of specific biomass growth rate and was independent of the dilution rate. Productivity is shown to be 12.5 times greater than in conventional continuous operation and is directly proportional to dilution rate. Maximum biomass concentration also presents a linear relationship with dilution rate. The largest obtained biomass concentration is 8 times greater than in a conventional continuous fermentor.     

Improved performance of intensive semicontinuous cultures of Scenedesmus by biomass recirculation

The microscopic green alga, Scenedesmus obliquus, was used in a semicontinuous culture system for the tertiary treatment of urban wastewater, with the simultaneous production of usable biomass. Partial biomass recycling was used to increase the productivity of the system by overcoming the limits imposed by the low maximal growth rate of the alga. The biomass to be recycled was collected by simple gravity settling of the removed culture.The culture system was operated at different dilution rates and its productivity measured at each rate. An evaluation of the crude nutrient composition of the algae produced at each dilution rate was also carried out.The system was found to operate stably at dilution rates of up to 0.8 day(-1) which represents a 20% net increase over the maximum dilution rate allowed under the same conditions in a system without recirculation. The composition of the biomass produced varied little over a range of dilution rates, which may be of relevance to its projected end-use.The study indicated that such a system can exploit available light to the full and should be of particular value for the treatment of low-strength wastes such as we employed.     

Buffering capacity as an indicator of physiological state in a continuous culture ofCandida utilis

Alkalimetric titration of the supernatant and the whole steady-state cell suspension was used to determine the buffering capacity of aCandida utilis culture during continuous cultivation at different dilution rates. Differences in the two types of titration curves were used to calculate, by means of the theory of dissociation of polyelectrolytes, the change in Gibbs free energy necessary to remove one proton from a live cell. The energy, 4.5 × 10^-20 J (0.28 eV), corresponded to the energy of hydrogen bonds. With increasing growth rate the quantity of these bonds per unit dry mass increased, in direct proportion to the sum of the content of proteins and RNA per unit biomass. They reflect the weak buffering forces exerted by cell macromolecules, which are measurable under our experimental conditions and may serve as a marker of the physiological state of the cells.     

Production of biomass and amylases by the yeast Lipomyces kononenkoae in starch-limited continous culture

Summary In strain IGC 4052 of the amylolytic yeast Lipomyces kononenkoae growing in starch-limited chemostat cultures the critical dilution rate was reduced to about half of its theoretical value due to severe catabolite repression of amylase formation while its value in a repression-resistant mutant was near its theoretical value. The enzyme yield coefficients and the specific production rates of α-amylase and glucoamylase passed through maxima at intermediate dilution rates. The shapes of the respective curves were partly determined by catabolite repression (parent strain) or its absence (mutant strain) while induction did not seem to play to role. An additional growth-linked regulatory mechanism seemed to be involved. The use of continuous culture as compared with batch culture, increased the maximum biomass productivity by a factor of 2.2 in the mutant strain and by a factor of 1.4 in the parent strain.     

Use of ATP to characterize biomass viability in freely suspended and immobilized cell bioreactors

This work describes investigations into the viability of cells growing on 3,4-dichloroaniline (34DCA). Two bioreactors are employed for microbial growth, a continuous stirred tank (CST) bioreactor with a 2-L working volume, and a three-phase air lift (TPAL) bioreactor with a 3-L working volume. Experiments have been performed at several dilution rates between 0.027 and 0.115 h(-1) in the CST bioreactor and between 0.111 and 0.500 h(-1) in the TPAL bioreactor. The specific ATP concentration was calculated at each dilution rate in the suspended biomass in both bioreactors as well as in the immobilized biomass in the TPAL bioreactor. The ATP was extracted from the cells using boiling tris-EDTA buffer (pH 7.75), and the quantity determined using a firefly (bioluminescence) technique. The cultures were inspected under an electron microscope to monitor compositional changes. Results from the CST bioreactor showed that the biomass-specific ATP concentration increases from 0.44 to 1.86 mg ATP g(-1) dry weight (dw) as dilution rate increases from 0.027 to 0.115 h(-1). At this upper dilution rate the cells were washed out. The specific ATP concentration reached a limiting average value of 1.73 mg ATP g(-1) dw, which is assumed to be the quantity of ATP in 100% viable biomass. In the TPAL bioreactor, the ATP level increased with dilution rate in both the immobilized and suspended biomass. The specific ATP concentration in the immobilized biomass increased from approximately 0.051 mg ATP g(-1) dw at dilution rates between 0.111 and 0.200 h(-1) to approximately 0.119 mg ATP g(-1) dw at dilution rates between 0.300 and 0.500 h(-1). This indicates that the immobilized biomass contained a viable cell fraction of around 5%. Based on these results, kinetic data for freely suspended cells should not be applied to the modeling of immobilized cell systems on the assumption that immobilized biomass is 100% viable. (c) 1993 John Wiley & Sons, Inc.     

棉花蕾花铃生物量、氮累积特征及临界氮浓度稀释模型

在大田栽培条件下,于河南安阳（黄河流域黄淮棉区）和江苏南京（长江流域下游棉区）设置了棉花氮素水平试验,对不同氮素水平条件下棉花蕾花铃的生物量、氮素累积及氮浓度的动态变化进行分析,并依据Justes的临界氮浓度稀释模型确定方法,研究棉花蕾花铃临界氮浓度稀释模型。结果表明：棉花蕾花铃的生物量增长和氮吸收累积均受氮素水平的影响,其动态变化符合S型曲线,氮累积的快速起始时间较生物量早1～5d;氮浓度过高或过低均不利于产量形成,蕾花铃等器官存在氮奢侈消费现象;氮浓度随施氮量的增加而升高、随生育进程的推移而降低,其生物量累积量与氮浓度间符合幂函数关系,两试点蕾花铃氮稀释曲线模型形式相同,但模型参数a不同,不同生态区存在独立的临界氮稀释曲线模型。由于临界稀释模型具有明确的生物学意义,可以作为定量诊断蕾花铃氮营养动态变化的指标之一。     

Controlled biomass formation and kinetics of toluene degradation in a bioscrubber and in a reactor with a periodically moved trickle-bed

The kinetics of degradation of toluene from a model waste gas and of biomass formation were examined in a bioscrubber operated under different nutrient limitations with a mixed culture. The applicability of the kinetics of continuous cultivation of the mixed culture was examined for a special trickle-bed reactor with a periodically moved filter bed. The efficiency of toluene elimination of the bioscrubber was 50 to 57% and depended on the toluene mass transfer as evident from a constant productivity of 0.026 g dry cell weight/L . h over the dilution rate. Under potassium limitation the biomass productivity was reduced by 60% to 0.011 g dry cell weight/L . h at a dilution rate of 0.013/h. Conversely, at low dilution rates the specific toluene degradation rates increased. Excess biomass in a trickle-bed reactor causes reduction of interfacial area and mass transfer, and increase in pressure drop. To avoid these disadvantages, the trickle-bed was moved periodically and biomass was removed with outflowing medium. The concentration of steady state biomass fixed on polyamide beads decreased hyperbolically with the dilution rate. Also, the efficiency of toluene degradation decreased from 72 to 56% with increasing dilution rate while the productivity increased. Potassium limitation generally caused a reduction in biomass, productivity, and yield while the specific degradation increased with dilution rate. This allowed the application of the principles of the chemostat to the trickle-bed reactor described here, for toluene degradation from waste gases. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 686-692, 1997.     

Modeling the growth and proteinase A production in continuous cultures of recombinant Saccharomyces cerevisiae

Overexpression of the homologous protein proteinase A (PrA) in Saccharomyces cerevisiae has been achieved by inserting the PrA gene (PEP4) with its own promoter on a 2mu multicopy plasmid. With this system the specific PrA production rate was found to be described well by a linear function of the oxidative glucose metabolism, the reductive glucose metabolism, and the oxidative ethanol metabolism, with a significant lower yield resulting from the reductive glucose metabolism compared with the oxidative glucose metabolism. To describe the experimental data, a simple mathematical model has been set up. The model is based on an assumption of a limited respiratory capacity as suggested by Sonnleitner and K?ppeli but extended to describe production of an extracellular protein. The model predicts correctly the critical dilution rate to be between 0.15 and 0.16 h(-1), the decrease in the biomass yield above the critical dilution rate, and the production of proteinase A at different dilution rates. Both the experimental data and model simulations suggest that the optimum operating conditions for protein production is just at the critical dilution rate. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 447-454, 1997.     

Continuous ethanol production from Jerusalem artichoke tubers. I. Use of free cells of Kluyveromyces marxianus

The Continuous fermentation of Jerusalem artichoke juice to ethanol by free cells of Kluyveromyces marxianus UCD (FST) 55-82 has been studied in a continuous-stirred-tank bioreactor at 35 degrees C and pH 4.6. A maximum yield of 90% of the theoretical was obtained at a dilution rate of 0.05 h(-1). About 95% of the sugars were utilized at dilution rates lower than 0.15 h(-1). Volumetric ethanol productivity and volumetric biomass productivity reached maximum values of 7 g ETOH/L/h and 0.6 g dry wt/L/h, respectively, at a dilution rate of 0.2 h(-1). The maintenance energy coefficient for K. marxianus culture was found to be 0.46 g sugar/g biomass/h/ Oscillatory behavior was following a change in dilution rate from a previous steady state and from batch to continuous culture. Values of specific ethanol production rate and specific sugar uptake were found to increase almost linearly with the increase of the dilution rate. The maximum specific ethanol production rate and maximum specific sugar uptake rate were found to be 2.6 g ethanol/g/ cell/h and 7.9 sugars/g cell/h, respectively. Washout occurred at a dilution rate of 0.41 h(-1).     

Activities of plasma membrane-bound enzymes isolated from roots of spruce (Picea abies) grown in the presence of aluminium

In batch cultures of Petunia hybrida cv. Rosy Morn Fertile. one respiratory peak is usually observed shortly after subculturing. However, two types of peak respiration could be distinguished, one connected with the dilution process and one with sugar addition at low biomass concentrations. The dilution peak was observed when cells were diluted in medium without sugar, in the presence or absence of mannitol. The sugar peak occurred only after previous dilution of the cells and not when sugar is added at high biomass concentrations Apparently the existence of a dilute suspension is a prerequisite for the induction of the peak. The presence of sugar is not a prerequisite for the increased respiratory activity but it is necessary lor growth: however, growth is possible without the increase in respiration, as was shown by the addition of sugar to a culture with a high biomass concentration. The peak caused by dilution either in the presence or absence of sugar showed no significant differences in height. The height of the peak caused by sugar addition to a previously diluted cell suspension was correlated with the sugar concentration. The respiratory peak disappeared long before the end of the growth period; this decline of the respiratory rates was not connected to sugar or oxygen limitation. In a continuous culture of Petunia hybrida growing at low biomass concentration, the respiration was always at the high level as observed during the peak of batch culture. Growing at lower biomass concentrations might be more expensive for plant cell suspensions.     

Utilization of mass–energy balance regularities in the analysis of continuous-culture data

Material and energy balances for continuous-culture processes are described based on the facts that the heat of reaction per electron transferred to oxygen for a wide variety of organic molecules, the number of available electrons per carbon atom in biomass, and the weight fraction carbon in biomass are relatively constant. Energy requirements for growth and maintenance are investigated and related to the biomass energetic yield. The consistency of experimental data is examined using material and energy balances and the regularities identified above. When extracellular products are absent, the consistency of yield models containing separate terms for growth and maintenance may be investigated using organic substrate consumption, biomass production, oxygen consumption (or heat evolution), and carbon dioxide evolution rate data for a series of dilution rates. The consistency of continuous-culture data in the published literature is examined.     

Continuous cultivation of the yeastSaccharomyces cerevisiae at different dilution rates and glucose concentrations in nutrient media

The influence of glucose concentration in nutrient media on the specific growth rate and biomass yield in the course of continuous fermentation ofSaccharomyces cerevisiae was investigated. An increase of glucose content in media decreased the specific growth rate and the biomass yield. Glucose concentration had significant effects on protein and phosphate contents of cells. However, an increased glucose concentration increased the fermentative power ofS. cerevisiae (SJA-method). An increase of the dilution rate decreased the cell concentration in the fermentor. Specific growth rate approached the values of the dilution rate. The best agreement has been obtained at a dilution rate of 0.20/h. This dilution rate proved to be most convenient for the investigated microorganism and cultivation conditions (media composition, pH, aeration intensity and temperature). Biomass yield proved to be decreased by an increase of the dilution rate.     

Theory for growth of plants derived from the nitrogen productivity concept

A theory is developed on the assumption that growth of plants is determined by the current amount of nitrogen in the plants. The nitrogen-growth relation is formalized in the nitrogen productivity concept (amount of biomass produced per amount of nitrogen in the biomass and per unit of time), which is essentially a constant for a given species under fixed environmental conditions. A number of results follow for increases in whole plant biomass: (A) The relative growth rate is a linear function of the internal nitrogen concentration. (B) The maximal relative growth rate uniquely determines the scaling of the time axis. (C) Exponential growth is consistent only with stable internal nitrogen concentration. Dose-response curves expressed in reduced variables (the ratio between a variable and the same variable for a plant growing under optimal conditions) are universal, so that all species and all environmental conditions yield the same curve. This is confirmed by experimental data. The shape (linear, exponential, etc.) of the nitrogen uptake curve is the only parameter differentiating these universal curves. The Mitscherlich curve or variations of it can be fitted very closely to the derived dose-response curves, except under exponential growth. A conclusion drawn from the analysis is that the results of nutrition experiments cannot be properly interpreted unless the variation with time of the amount of nitrogen in the plant is known. The theory can be extended to more complex situations, for example, time-varying environmental conditions.     

Dynamics of anaerobic growth of Saccharomyces cerevisiae in the chemostat.

A kinetic Monod model has been used to describe the dynamic response of a continuous stirred tank fermentor (CSTF) to changes in dilution rate. A general analytical solution of a linearized model was obtained. Experimental results (Vairo et al. 1977) of continuous anaerobic culture of Saccharomyces cerevisiae have verified the model quantitatively. For step disturbances on the dilution rate the responses of biomass concentration and the outlet substrate concentration were calculated on a digital computer and compared with the experimental data.     

Fluctuations in continuous mammalian cell bioreactors with retention.

Continuous flow bioreactors with cell retention have been increasingly used for the cultivation of mammalian cells. The potential advantages of such bioreactors are high cell concentrations and volumetric productivities. In many reported cases, these systems have shown fluctuations in cell concentrations of various frequency and magnitude. To analyze the dynamics of the fluctuations, a model-based approach is followed. Simulations showed that large fluctuations in biomass resulted in response to fluctuations in the retention ratio when the system is operated at high dilution rate and high cell retention. The dependence of cell concentration fluctuations on variations in dilution rate and retention ratio was established by a cross-correlation statistical analysis on available experimental data. The slower dynamics and the fluctuation propensity of retention systems suggest that continuous culture without retention is more convenient for kinetic studies. In all likelihood, continuous culture with retention can be stabilized by controlling both the retention ratio and the dilution rate.     

Optimization of Phaffia rhodozyma continuous culture through response surface methodology

Response surface methodology was applied to optimize the growth of the yeast Phaffia rhodozyma in continuous fermentation using peat hydrolysates as substrate. A second-order, complete, factorial design of the experiments was used to develop empirical models providing a quantitative interpretation of the relationships between the two variables studied, dilution rate and pH. Maximum biomass concentration in the fermentor was obtained by employing the following predicted optimum fermentation conditions: a dilution rate of 0.017/h and a pH level of 7.19. A verification experiment, conducted at previously optimized conditions for maximum biomass volumetric productivity (a dilution rate of 0.022/h, and a pH level of 6.90), produced values for biomass concentration, residual substrate concentration, biomass yield, and biomass volumetric productivity that were very close to the predicted values, indicating the reliability of the empirical model. The concentration of the pigment astaxanthin produced by the yeast under the optimized growth conditions was found to be 544 mg astaxanthin/kg dry cell biomass.     

In situ pulse respirometric methods for the estimation of kinetic and stoichiometric parameters in aerobic microbial communities

In situ pulse respirometry was applied in an activated sludge bubble column treating synthetic wastewater for the estimation of the (i) maximum specific oxygen consumption rate, (ii) substrate affinity constant, (iii) biomass growth yield, (iv) maintenance coefficient, and (v) specific endogenous respiration rate. Parameters obtained from respirometry were compared to those obtained by the chemostat method, based on substrate and biomass measurements, under several dilution rates. The low sensitivity of substrate measurement methods and the difficulties of sampling heterogeneous biomass suspension are critical issues limiting the applicability of the chemostat method. Additionally, the extensive time consuming nature of this method allows concluding that chemostat method presents several disadvantages in comparison with in situ pulse respirometric techniques. Parameters were obtained from respirograms by fitting ASM1 and ASM3 models, and from experiments performed by injecting pulses of increasing substrate concentration. The injection of pulses of increasing concentration was the most adequate method, with several advantages such as a simpler experimental data interpretation, and results with better confidence.Considering the assessment and comparison of the experimental and calculation methods presented, it is recommended that the estimation of kinetic and stoichiometric parameters in mixed aerobic cultures should preferentially be performed by using in situ respirometric techniques.     

Modeling of ferrous iron oxidation by a Leptospirillum ferrooxidans-dominated chemostat culture

The objective of this study was to evaluate a direct classical bioengineering approach to model data generated from continuous bio-oxidation of Fe(2+) by a Leptospirillum ferrooxidans-dominated culture fed with either 9 g or 18 g Fe(2+) L(-1) under chemostat conditions (dilution rates were between 0.051 and 0.094 h(-1)). The basic Monod and Pirt equations have successfully been integrated in an overall mass balance procedure, which has not been previously presented in this detail for Fe(2+) oxidation. To ensure chemostat conditions, it was found that the range of the dilution rates had to be limited. A too long retention time might cause starvation or non-negligible death rate whereas, a too short retention time may cause a significant alteration in solution chemistry and culture composition. Modeling of the experimental data suggested that the kinetic- and yield parameters changed with the overall solution composition. However, for respective feed solutions only minor changes of ionic strength and chemical speciation can be expected within the studied range of dilution rates, which was confirmed by thermodynamic calculations and conductivity measurements. The presented model also suggests that the apparent Fe(3+) inhibition on specific Fe(2+) utilization rate was a direct consequence of the declining biomass yield on Fe(2+) due to growth uncoupled Fe(2+) oxidation when the dilution rate was decreased. The model suggested that the maintenance activities contributed up to 90% of the maximum specific Fe(2+) utilization rate, which appears close to the critical dilution rate. Biotechnol. Bioeng. 2008;99: 378-389. (c) 2007 Wiley Periodicals, Inc.