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Continuous Cultivation (continuous + cultivation)
Selected AbstractsContinuous Cultivation of the Diatom Nitzschia laevis for Eicosapentaenoic Acid Production: Physiological Study and Process OptimizationBIOTECHNOLOGY PROGRESS, Issue 1 2002Zhi-You Wen The continuous cultures of the diatom Nitzschia laevis were performed at different dilution rates ( D) and feed glucose concentrations ( S0) to investigate cellular physiological responses and its production potential of eicosapentaenoic acid (EPA). Steady-state cell dry weight, residual glucose concentration, cell growth yield, specific glucose consumption rate, and fatty acid profiles were investigated within the range of D from 0.1 to 1.0 day,1 ( S0 fixed at 20 g/L) and the range of S0 from 5 to 35 g/L ( D fixed at 0.3 day,1), respectively. The highest EPA productivity of 73 mg L -1 day -1 was obtained at D = 0.5 day,1 and S0 = 20 g/L. However, when the continuous culture achieved high productivities of EPA at certain dilution rates and feed glucose concentrations, glucose in the feed could not be consumed completely. Accordingly, the continuous culture was evaluated in terms of both EPA productivity ( P) and glucose assimilation efficiency ( E). The parameter ,, defined as the product of P and E, was used as an overall performance index. Since , is a function of the two independent variables Dand S0, we employed a central composite design to optimize D and S0 for the highest , value. Based on the experimental results of the design, a second-order polynomial equation was established to represent the relationship between , and D and S0. The optimal values of D and S0 were subsequently determined as 0.481 day,1 and 15.56 g/L, respectively by the empirical model. The verification experiment confirmed the validity of the model. Under the optimal conditions, , value reached 46.5 mg L -1 day -1, suggesting a considerably high efficiency of the continuous culture of N. laevis in terms of EPA production and glucose utilization. [source] Changes in microbial community composition following treatment of methanogenic granules with chloroformENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 1 2009Bo Hu Abstract Eliminating hydrogen consuming bacteria is a critical step in anaerobic fermentation for biohydrogen production. Treatment of anaerobic granular sludge with chloroform was reported as effective in transforming a methane-producing system into a hydrogen-producing system by eliminating methane production. This study, using 16S rRNA gene sequences, further assessed changes in microbial community composition as a result of chloroform treatment and during continuous cultivation of chloroform-treated granules in a continuous upflow reactor employing immobilized cells. Profiles of terminal restriction fragment length polymorphisms (T-RFLP) of 16S rRNA genes sequences cloned from samples before and after chloroform treatment showed that methanogenic hydrogen consumers and Methanosaeta harundinacea sp. were eliminated. Methanosaeta concilii, however, was not eliminated from the hydrogen-producing system, which might explain, in part, the granulation phenomena in the anaerobic hydrogen fermentation system. The results also showed that Clostridium butyricum dominated the hydrogen-production system. © 2009 American Institute of Chemical Engineers Environ Prog, 2009 [source] Resistance of potato cultivars to Synchytrium endobioticum in field and laboratory tests, risk of secondary infection, and implications for phytosanitary regulationsEPPO BULLETIN, Issue 1 2005R. P. Baayen Laboratory (Spieckermann) tests, pot tests and field tests provided concordant evidence for the partial nature of resistance of potatoes to pathotypes 1 (D1) and 6 (O1) of Synchytrium endobioticum. Susceptible potato cultivars produced large warts (> 16 mm in diameter) in Spieckermann tests and had low field resistance levels (1,6). Field-resistant cultivars (levels 7,9) produced small warts or no warts at all in Spieckermann and field tests. In pot tests, at low inoculum levels (1 sporangium per 25 g soil) susceptible cultivars still developed warts, whereas field-resistant ones did not develop any warts below 25 sporangia per g soil. Above 35 sporangia per g soil, 100% disease incidence was observed in susceptible cultivars but only minimal wart development in field-resistant ones. Tests with continuous cultivation of potato cultivars in infected soil during three consecutive years showed that field-resistant cultivars will not support build-up of inoculum in soil. It is concluded that field-resistant cultivars do not create a risk of secondary infection, the criterion given for resistance in EU Directive 69/464/EC. [source] Loss of phosphorus from soil in semi-arid northern Tanzania as a result of cropping: evidence from sequential extraction and 31P-NMR spectroscopyEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000D. Solomon Summary In semi-arid northern Tanzania, the native woodland is being rapidly cleared and replaced by low input agriculture. This has resulted in pronounced environmental degradation, and in particular loss of phosphorus (P) from the soil. We have used sequential extraction and 31P-NMR to investigate the effects of land use changes, i.e. native woodland, degraded woodland, cultivation for 3 and 15 years and homestead fields where manure was applied, on the amount and structural composition of P in this soil. Clearing and continuous cultivation reduced both organic and inorganic P in the soil. The difference in the amount of organic P from the bulk soil of the fields cultivated for 3 and 15 years was not statistically significant (P <,0.05), suggesting that most of the depletion in organic P occurred during the first 3 years of cultivation. By contrast, in the homesteads, there was much organic and inorganic P in the soil. The 31P-NMR revealed that cultivation resulted in a 53% depletion of orthophosphate diester P, whereas only a 30% and 39% reduction of orthophosphate monoester P was found in the bulk soil after 3 and 15 years of cultivation, respectively. These results concur with the suggestion that diester P constitutes more easily mineralizable forms of organic P in soil than does monoester P. Our 31P-NMR also showed that 70% of the inorganic orthophosphate P was depleted from the coarse and fine sand separates as a result of cultivation. The influence of clearing and subsequent cropping on the amount and forms of P was more pronounced in the coarse and fine sand than in the silt and clay, stressing the importance of particle size and chemical properties such as organic matter and oxides in the availability of P in this soil. Our results show that the current low input agricultural practice is not sustainable, and that practices must be developed to combat the ongoing degradation of the soil. A combined use of available organic materials such as animal manure with the judicious use of inorganic fertilizers can replenish the soil's fertility. [source] Nutrient constraints to tropical agroecosystem productivity in long-term degrading soilsGLOBAL CHANGE BIOLOGY, Issue 12 2008SOLOMON NGOZE Abstract Soil degradation is one of the most serious threats to sustainable crop production in many tropical agroecosystems where extensification rather than intensification of agriculture has occurred. In the highlands of western Kenya, we investigated soil nitrogen (N) and phosphorus (P) constraints to maize productivity across a cultivation chronosequence in which land-use history ranged from recent conversion from primary forest to 100 years in continuous cropping. Nutrient treatments included a range of N and P fertilizer rates applied separately and in combination. Maize productivity without fertilizer was used as a proxy measure for indigenous soil fertility (ISF). Soil pools of mineral nitrogen, strongly bound P and plant-available P decreased by 82%, 31% and 36%, and P adsorption capacity increased by 51% after 100 years of continuous cultivation. For the long rainy season (LR), grain yield without fertilizer declined rapidly as cultivation age increased from 0 to 25 years and then gradually declined to a yield of 1.6 Mg ha,1, which was maintained as time under cultivation increased from 60 to 100 years. LR grain yield in the old conversions was only 24% of the average young conversion grain yield (6.4 Mg ha,1). Application of either N or P alone significantly increased grain yield in both the LR and short rainy (SR) seasons, but only application of 120 kg N ha,1 on the old conversion increased yield by >1 Mg ha,1. In both SR and LR, there was a greater average yield increment response to N and P when applied together (ranging from 1 to 3.8 Mg ha,1 for the LR), with the greatest responses on the old conversions. The benefit,cost ratio (BCR) for applying 120 kg N ha,1 alone was <1 except on the old conversions, while BCRs were>1 for applying 25 kg P ha,1 alone at all levels of conversion for both seasons. Application of both N (120 kg N ha,1) and P (25 kg P ha,1) on the old conversions resulted in the greatest BCRs. This study clearly indicates that maize productivity responses to N and P fertilizer are significantly affected by the age of cultivation and its influence on ISF, but that loss of productivity can be restored rapidly when these limiting nutrients are applied. Management strategies should consider ISF and economic factors to determine optimal N and P input requirements for achieving and sustaining profitable crop production on degraded soils. [source] Optimal mixing to improve the performance of batch and continuous fermentations with recombinant Escherichia coliJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2005Venkata SRK Ganduri Abstract Fermentations with genetically altered bacteria tend to lose plasmids as the fermentation progresses. Methods such as two-stage cultivation, cell recycle and the addition of antibiotics are commonly used to enhance plasmid stability. Here we examine a different method, the regulation of mixing in the bioreactor. In particular, large bioreactors are considered where uniform mixing is difficult to achieve and the probability of plasmid loss varies with the specific growth rate. For both batch and continuous cultivations of Escherichia coli C600 gal K containing the plasmid pBR Eco gap, it is seen through a model that both modes of operation exhibit high plasmid stability and cell growth when the broth is incompletely mixed, and mixing near and away from the point of inoculation are unequal. Thus, the natural incomplete mixing in large bioreactors may be utilized to improve plasmid stability. A practical method to implement this idea is suggested. Copyright © 2005 Society of Chemical Industry [source] | ||||||||||