Energy requirements for growth and maintenance of Scenedesmus protuberans Fritsch in light-limited continuous cultures

Scenedesmus protuberans Fritsch was grown in light-limited continuous cultures with a light-dark cycle, at temperatures of 20° and 28° C. At 20° irradiances of 12 and 38 W m^–2 were used, at 28° 38 W m^–2.The relationships between growth rate and light uptake rate were of diphasic linear character. With the lower growth rates the relationships were defined with the parameters _e , i.e. the specific maintenance rate constant, and c, the true efficiency of light energy conversion into biomass. The _e -value was dependent on temperature, the c on irradiance.In cultures, incubated in prolonged darkness, decrease rates of biomass were comparable to the derived _e -values.Both diphasic linear relationships between growth rate and light uptake rate and the same order of magnitude of _e -values could be derived from literature data on other green algae.     

Principles of the light-limited chemostat: theory and ecological applications

Light is the energy source that drives nearly all ecosystems on planet Earth. Yet, light limitation is still poorly understood. In this paper, we present an overview of the principles of the light-limited chemostat. The theory for light-limited chemostats differs considerably from the standard theory for substrate-limited chemostats. In particular, photons cannot be mixed by vigorous stirring, so that phototrophic organisms experience the light-limited chemostat as a heterogeneous environment. Similar to substrate-limited chemostats, however, light-limited chemostats do reach a steady state. This allows the study of phototrophic microorganisms under well-controlled light conditions, at a constant specific growth rate, for a prolonged time. The theory of the light-limited chemostat is illustrated with several examples from laboratory experiments, and a variety of ecological applications are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

不同生育期降低光强对烟草生长发育和品质的影响

2004-2005年在烤烟生长发育的不同时期进行遮荫降低光照强度的盆栽试验,研究了不同生育期降低光强对烤烟生长发育和品质的影响.结果表明:遮荫条件下烟株干物质积累下降,叶片组织变薄,色素含量升高,落黄成熟时间延长;转化酶活性降低,但遮荫解除后又开始升高;叶片烤后烟叶含梗率增加,叶片厚度和比叶质量降低,烟碱、总氮、钾和氯含量增加,总糖和还原糖含量降低,中性致香成分含量增加.不同时期遮荫的影响为成熟期＞旺长期＞伸根期＞对照.     

Comparison of the light-limited growth of the nitrogen-fixing cyanobacteria Anabaena and Aphanizomenon

The effect of simultaneous N₂ fixation and light limitation on the growth of two strains of Anabaena sp. Bory de St. Vincent and Aphanizomenon flos-aquae (L.) Ralfs was investigated using continuous cultures. Under severely light-limited conditions, Aphanizomenon showed a broader absorption spectrum (due to the presence of phycoerythrin), a higher maximum efficiency of photosynthesis, a higher steady-state N₂ fixation activity and a higher growth affinity for light than did Anabaena . On the other hand, under light saturation, Anabaena showed a higher maximum rate of O₂ production and a higher maximum specific growth rate than Aphanizomenon . These monoculture results characterize Anabaena and Aphanizomenon , in relative terms, as a 'sun' and a 'shade' species respectively, and are in accordance with field observations. The difference between the two species in their acclimatory response is discussed in terms of a species-specific alteration of the PSI:PSII stoichiometry. Besides the species-specific modulation of the accessory pigments, such an acclimation would provide a biochemical basis for the observed physiological differences. The monoculture results were used to differentiate the niches of the two species and suggested that Aphanizomenon would competitively displace Anabaena under N₂-fixing, light-limited conditions. However, when both species were grown together, Anabaena became dominant and seemed to be the superior competitor for light. In order to explain this finding, the possible effects of release of allelopathic compounds, or dynamic aspects of light supply, are discussed.     

Comparison of specific rates of hybridoma growth and metabolism in batch and continuous cultures

For the mouse hybridoma cell line VO 208, kinetics of growth, consumption of glucose and glutamine, and production of lactate, ammonia and antibodies were compared in batch and continuous cultures. At a given specific growth rate, different metabolic activities were observed: a 40% lower glucose and glutamine consumption rate, but a 70% higher antibody production rate in continuous than in batch culture. Much higher metabolic rates were also measured during the initial lag phase of the batch culture. When representing the variation of the specific antibody production rate as a function of the specific growth rate, there was a positive association between growth and antibody production in the batch culture, but a negative association during the transient phase of the continuous culture. The kinetic differences between cellular metabolism in batch and continuous cultures may be result of modifications in the physiology and metabolism of cells which, in continuous cultures, were extensively exposed to glucose limitations.Institut National Polytechnique de Lorraine, ENSAIA BP 172, 2 avenue de la forêt de Haye, 54505, Vandoeuvre Cedex France     

遮阴对两种泥炭藓植物生长及相互作用的影响

以大泥炭藓和喙叶泥炭藓为材料,研究遮阴对其生长及植物相互作用的影响.结果表明:在单种群中,遮阴处理明显促进了大泥炭藓的高生长,但对喙叶泥炭藓的生长以及大泥炭藓生物量和分枝数未产生影响;在混合群中,喙叶泥炭藓抑制了大泥炭藓生物量和分枝数的增长,而大泥炭藓对喙叶泥炭藓的生长无影响.随遮阴胁迫的增加,邻体对喙叶泥炭藓竞争加剧,当胁迫进一步增强,邻体效应有转变为正相互作用的趋势,但邻体对大泥炭藓的效应始终为竞争,未随胁迫增加而变化.     

Modelling continuous culture of Rhodospirillum rubrum in photobioreactor under light limited conditions

Rhodospirillum rubrum was grown continuously and photoheterotrophically under light limitation using a cylindrical photobioreactor in which the steady state biomass concentration was varied between 0.4 to 4 kg m^–3 at a constant radiant incident flux of 100 W m^–2. Kinetic and stoichiometric models for the growth are proposed. The biomass productivities, acetate consumption rate and the CO₂ production rate can be quantitatively predicted to a high level of accuracy by the proposed model calculations. Nomenclature: C _X, biomass concentration (kg m^–3) D, dilution rate (h^–1) Ea, mean mass absorption coefficient (m² kg^–1) I , total available radiant light energy (W m^–2) K, half saturation constant for light (W m^–2) R _W, boundary radius defining the working illuminated volume (m) r _X, local biomass volumetric rate (kg m^–3 h^–1) <r _X>, mean volumetric growth rate (kg m^–3 h^–1) V _W, illuminated working volume in the PBR (m^–3). Greek letters: , working illuminated fraction (–) _M, maximum quantum yield (–) bar, mean energetic yield (kg J^–1).     

Some observations on protease production in continuous suspension cultures of Bacillus firmus

Invariance of culture conditions in steady state continuous cultures make these a very valuable tool to study the influence of various culture parameters on cell growth and synthesis of primary and secondary metabolites. The result of a parametric study on production of protease in continuous suspension cultures of Bacillus firmus NRS 783 are reported in this article. This strain is a superior producer of an alkaline protease with major application in the detergent industry. The parameters investigated include dilution rate and concentrations of yeast extract, ammonium, and inorganic phosphate in the bioreactor feed, glucose being the principal carbon source in all experiments. The regulatory effects of the key culture parameters on cell growth, synthesis and secretion of protease, and production of acetic acid are investigated. The relations among the specific cell growth rate, specific utilization rates of the principal carbon, nitrogen, and phosphorous sources, and specific production rates of two nonbiomass products, viz., acetic acid and protease, are examined, and the effects of the manipulated culture parameters on these relations, specific protease activity, and yields of cell mass, protease, and acetic acid on the basis of the principal carbon, nitrogen, and phosphorous sources are studied. An increase in dilution rate led to increases in specific utilization rates of the principal carbon, nitrogen, and phosphorous sources and specific production rates of acetic acid and protease and decreases in bulk activities/concentrations of the three products (acetic acid, cell mass, and protease). As a result, the productivities of the three species were maximized at an intermediate dilution rate. Increased supply of yeast extract (a rich source of amino acids, proteins, and vitamins, besides being an additional source of carbon, nitrogen, and phosphorus) promoted cell mass formation but reduced protease production per unit cell mass. Increased supply of nitrogen and phosphorous sources stimulated protease synthesis up to certain threshold levels and repressed the enzyme synthesis beyond the threshold levels. With increased supply of the nitrogen source, the phosphorous source was more efficiently utilized for cell growth and protease synthesis. Stable maintenance of continuous cultures of B. firmus over prolonged period is demonstrated in this study. (c) 1993 John Wiley & Sons, Inc.     

Glucoamylase production in continuous cultures of Aspergillus niger with special emphasis on growth parameters

Maltose-limited continuous culture of Aspergillus niger was carried out with potassium nitrate to investigate growth and glucoamylase formation characteristics. Glucoamylase production was dependent on the specific growth rate. The maximal amount of glucoamylase (units/l and U/g dry weight) was obtained at =0.08h–1, and the maximum specific rate of production (units/g/dry weight per hour) was at =0.2h–1. The maintenance coefficients (ms and mATP) were higher than for some other fungi. Maximal growth yields on substrate, oxygen and ATP (Yxsm, YxO2m and Yxam) were very efficient (high) and the value of Yxam, which cannot exceed the theoretical maximal value, is obtained when a P/O ratio of 1:1 is assumed. This indicates that biomass formation is energetically inexpensive and most of the expended energy has to be invested in the process of glucoamylase excretion.     

Studies on microbial chromate reduction by Pseudomonas Sp. In aerobic continuous suspended growth cultures

Reduction of hexavalent chromium was studied in three bench-scale continuous stirred tank reactors. The inoculum was a culture of Pseudomonas sp., capable of giving 83% to 87% chromate reduction in 72-h batch assays with 60 mg Cr(VI) L(-1) in synthetic medium. The continuous culture studies were conducted for about 100 days using synthetic feed containing different levels of chromate (5 to 124 mg L(-1)) at 28 degrees to 30 degrees C and pH 6.8. The feed rate was varied over the range 0.5 to 1 L d(-1) to obtain hydraulic retention time of 36 to 72 h. Chromate reduction efficiency was 81% to 91% and 100% for influent Cr(VI) concentrations of 15 to 124 and 5 mg L(-1), respectively, with a hydraulic retention time of 72 h. (c) 1994 John Wiley & Sons, Inc.     

Metabolic regulation in bacterial continuous cultures: II

The transient behavior of a continuous culture of Klebsiella pneumoniae with mixed feed of glucose and xylose arising from step-up and step-down in dilution rates and from a feed-switching experiment is presented. he organism gradually switches from simultaneous utilization of the substrates at low growth rates to preferred utilization of the faster substrate (i.e, supporting a higher growth rate) at high dilution rates. The metabolic lags following a step increase in dilution rate and a significant accumulation of the slower substrate during the transient period result from the effects of metabolic regulation. The cybernetic modeling approach that successfully described the foregoing situations with single-substrate feeds is employed to describe mixed substrate behavior. The parameters in the mixed-substrate (glucose and xylose) model are the same as those in the single-substrate models with the singular exception of the rate constant for the xylose growth enzyme synthesis. The reason for this discrepancy is discussed in detail. It appears that the constitutive rate of enzyme synthesis for growth on a given substrate may be related to the past history of the organism in regard to whether or not the organism has been exposed to the particular substrate. Thus, the results further demonstrate the ability of the framework to effectively describe metabolic regulation in batch, fedbatch, and continuous microbial cultures.     

Axenic cultures for microalgal biotechnology: Establishment,assessment, maintenance,and applications

The impact of microalgae (including blue-green algae or cyanobacteria) on human life can be both beneficiary and deleterious. While microalgae can be cultivated and used as feedstocks for the production of bioenergy and high value-added products in nutraceuticals, pharmaceuticals, and aquaculture feeds, some microalgae cause harmful algal blooms (HABs) that cause large-scale mortality in aquatic environments around the world. Thus, with the development of microalgal biotechnology and increasing concern about HABs, research on microscopic algae has increased significantly. However, this growth of academic research and application fields has been hindered by difficulties in obtaining axenic cultures. Therefore, this review provides a brief explanation of diverse establishment techniques, along with their strengths and weaknesses, with the hope of facilitating successful axenic cultures. A compilation of research fields and relevant important findings is also presented to clarify the importance of pure algal cultures. Finally, several controversial and sometimes overlooked issues related to the establishment, maintenance, and utilization of axenic cultures are discussed.     

Induction and long-term maintenance of Thy-1 positive T lymphocytes: Derivation from continuous bone marrow cultures

In the present study we investigated the presence of T-lymphocyte progenitors in the long-term murine bone marrow culture system described by Dexter: mature Thy-1 antigen-bearing T lymphocytes are lost in these cultures after a few days. By culturing nonadherent cells from such cultures in the presence of a supernatant of concanavalin A-stimulated spleen cells, a source of T-cell growth factor, we found that Thy-1 positive blast cells proliferated together with a second population of Thy-1 negative cells. These two populations of cells have been maintained in long-term in vitro cultures by passaging the cells in fresh conditioned medium at regular intervals. Moreover, we have been able to establish pure cultures of the Thy-1-bearing blast cells after separating them from the non-T cells using their adherence property to plastic surfaces. Long-term cultures of T lymphocytes can thus be established from long-term marrow cultures as well as from the spleen, thymus or fresh bone marrow.     

Photoautotrophic nutrient utilization and limitation during semi‐continuous growth of Synechocystis sp. PCC6803

Microbial photosynthesis presents a valuable opportunity to capture abundant light energy to produce renewable bioenergy and biomaterials. To understand the factors that control the productivity of photosynthetic microorganisms, we conducted a series of semi‐continuous experiments using bench‐scale photobioreactor (PBR) systems, the cyanobacterium Synechocystis PCC6803 (PCC6803), and light conditions imitating actual day–night light irradiance (LI). Our results demonstrate that using normal BG‐11 medium resulted in severe phosphate (P_i) limitation for continuous operation. Mitigation of P_i‐limitation, by augmenting the P_i content of BG‐11, allowed higher biomass productivity; however, once P_i‐limitation was alleviated, limitation by inorganic carbon (C_i) or LI occurred. C_i‐limitation was detected by a low total C_i concentration (<5 mg C/L) and high and fluctuating pH. C_i‐limitation was relieved by delivering more CO₂, which led to a stable pH in the range of 7–9 and at least 5 mg/L of C_i in HCO. LI limitation, evidenced by an average LI <14 W/m² for PCC6803, was induced by a high biomass concentration of 1,300 mg/L. Thus, this work provides quantitative tools of stoichiometry and kinetics to evaluate limitation on PBRs. Biotechnol. Bioeng. 2010;106: 553–563. © 2010 Wiley Periodicals, Inc.     

Avoiding rapid growth at high cell densities: A potentially important optimisation criterion for hybridoma cultures

Inhibition caused by rapid changes in the environment has earlier been observed in hybridoma cultures following deliberate step-changes in the culture environment. This paper presents evidence of similar effects occurring during the normal span of continuous cultures fed enriched medium at low dilution rates (0.002–0.005 1/h). The effect of this observation on optimisation is discussed. In continuous culture at a dilution rate of 0.013 1/h, a viable cell density of 4×10⁹ cells/l was achieved by gradually increasing the nutrient concentration in the feed medium. The MAb titre was 200 mg/l representing a 6-fold increase compared to batch culture and a 2-fold increase compared to continuous culture using standard medium.     

Simultaneous production of inulase and lactase in batch and continuous cultures of Kluyveromyces fragilis

Under different induction conditions, the industrial yeast Kluyveromyces fragilis is an excellent producer of the enzymes inulase (β-d-fructofuranoside fructohydrolase, EC 3.2.1.26) and lactase (β-d-galactoside galactohydrolase, EC 3.2.1.23), producing 27 and 1.6 U mg^?1dry cell weight, respectively. In order to improve overall enzyme yields, conditions for the simultaneous production of both enzymes in a one-stage fermentation have been examined. Techniques employed include carbon-limited batch and continuous culture, single and mixed carbon substrates, and the use of a mutant semi-constitutive for inulase production. Synthesis of both enzymes suffered strongly from carbon catabolite repression in batch cultures grown on single and mixed inducing substrates. Only glycerol and dl-malate did not repress either enzyme. The non-metabolizable analogues of lactose, isopropyl-β-d-thiogalactoside and methyl-β-d-thiogalactoside induced lactase in glycerol grown batch cultures, but were ineffective in sucrose grown continuous cultures. They also depressed the normally high levels of inulase in such continuous cultures. The highest simultaneous inulase and lactase activities in the wild-type yeast were obtained in continuous culture on an equal mixture of d-fructose and d-galactose; 25 and 0.78 U mg^?1dry cell weight, respectively. In this fermentation the combined yield per unit carbon substrate of the two enzymes was 141%, compared to a reference value of 100% for the highest yield of each enzyme in separate fermentations. On the same mixture of d-fructose and d-galactose, the mutant produced ～60 and 0.70 U mg^?1dry cell weight, respectively. The combined enzyme yield per unit of carbon substrate was 172%.     

Kinetic study of hybridoma cell growth in continuous culture: II. Behavior of producers and comparison to nonproducers

A hybridoma cell line, AFP-27-P, was cultivated in continuous culture under glucose-limited conditions. The viable cell concentration, dead-cell concentration, and cell volume all varied with the dilution rate. A model previously developed for a nonproducing clone of the same cell line, AFP-27-NP, was extended to describe the behavior of the cells. The relationship between the specific growth rate and glucose concentration is described by a function similar to the Monod model. A threshold glucose concentration and a minimum specific growth rate are incorporated; the model is meaningful only at glucose concentration and a minimum specific growth rate are incorporated; the model is meaningful only at glucose concentrations and specific growth rates above these levels. The relationship between the death rate and the glucose concentration is described by an inverted Monod-type function. Furthermore, the yield coefficient based on glucose is constant in the lower range of specific growth rates and changes to a new constant value in the upper range of specific growth rates. No maintenance term for glucose consumption is used; in the plot of specific glucose consumption rate vs. specific growth rate, the line intercepts the specific growth rate at a value close to the minimum growth rate. The productivity of antibody as a function of the specific growth rate is described by a mixed type model with a noon-growth-associated term and a negative-growth-associated term. The values for the model parameters were determined from regression analysis of the steady state data.