Maximum Specific Growth Rate (maximum + specific_growth_rate)

Distribution by Scientific Domains

Selected Abstracts

A dietary energy level of 14.6 MJ kg,1 and protein-to-energy ratio of 20.2 g MJ,1 results in best growth performance and nutrient accretion in silver barb Puntius gonionotus fingerlings

Abstract Five iso-nitrogenous (300 g protein kg,1 diet) and iso-lipidic (80 g kg,1 diet) semi-purified experimental diets with variable energy levels of 10.5 (D-1), 12.5 (D-2), 14.6 (D-3), 16.7 (D-4) and 18.8 (D-5) MJ kg,1 diets were fed to Puntius gonionotus fingerlings (average weight 1.79 0.02 g) in triplicate groups (15 healthy fishes per replicate) for a period of 90 days to assess the optimum dietary energy level and protein-to-energy ratio (P/E). Fifteen flow-through cement tanks of 100 L capacity with a flow rate of 0.5 L min,1 were used for rearing the fish. Maximum specific growth rate, protein efficiency ratio, protein productive value, RNA : DNA ratio, whole body protein content, digestive enzyme activity and minimum feed conversion ratio was found in fish-fed diet D-3 with 14.6 MJ kg,1 energy level. There were no improvements in all these parameters with the further rise in dietary energy level. Hence, it may be concluded that the optimum dietary gross energy level for maximum growth and nutrient utilization of silver barb is 14.6 MJ kg,1 diet with a resultant P/E ratio of 20.2 g protein MJ,1 diet, when the dietary protein and lipid are maintained at optimum requirement levels of 300 and 80 g kg,1 diet, respectively, for this species. [source]

Quantitative dietary threonine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

Ming-Yan Huai
Abstract An 8-week feeding trial was conducted to determine the threonine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50,1.50 g L,1). Diets 1,6 were formulated to contain 360 g kg,1 crude protein with fish meal, wheat gluten and pre-coated crystalline amino acids with six graded levels of l -threonine (9.9,19.0 g kg,1 dry diet). Diet 7, which was served as a reference, contained only intact proteins (fish meal and wheat gluten). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.480.01 g), each four times daily. Shrimps fed the reference diet had similar growth performance and feed utilization efficiency compared with shrimps fed the diets containing 13.3 g kg,1 or higher threonine. Maximum specific growth rate (SGR) and protein efficiency ratio were obtained at 14.6 g kg,1 dietary threonine, and increasing threonine beyond this level did not result in a better performance. Body compositions, triacyglycerol and total protein concentrations in haemolymph were significantly affected by the threonine level; however, the threonine contents in muscle, aspartate aminotransferase and alanine aminotransferase activities in haemolymph were not influenced by the dietary threonine levels. Broken-line regression analysis on SGR indicated that optimal dietary threonine requirement for L. vannamei was 13.6 g kg,1 dry diet (37.8 g kg,1 dietary protein). [source]

Generation of the improved recombinant xylose-utilizing Saccharomyces cerevisiae TMB 3400 by random mutagenesis and physiological comparison with Pichia stipitis CBS 6054

C.Fredrik Wahlbom
Abstract The recombinant xylose-utilizing Saccharomyces cerevisiae TMB 3399 was constructed by chromosomal integration of the genes encoding d -xylose reductase (XR), xylitol dehydrogenase (XDH), and xylulokinase (XK). S. cerevisiae TMB 3399 was subjected to chemical mutagenesis with ethyl methanesulfonate and, after enrichment, 33 mutants were selected for improved growth on d -xylose and carbon dioxide formation in Durham tubes. The best-performing mutant was called S. cerevisiae TMB 3400. The novel, recombinant S. cerevisiae strains were compared with Pichia stipitis CBS 6054 through cultivation under aerobic, oxygen-limited, and anaerobic conditions in a defined mineral medium using only d -xylose as carbon and energy source. The mutation led to a more than five-fold increase in maximum specific growth rate, from 0.0255 h,1 for S. cerevisiae TMB 3399 to 0.14 h,1 for S. cerevisiae TMB 3400, whereas P. stipitis grew at a maximum specific growth rate of 0.44 h,1. All yeast strains formed ethanol only under oxygen-limited and anaerobic conditions. The ethanol yields and maximum specific ethanol productivities during oxygen limitation were 0.21, 0.25, and 0.30 g ethanol g xylose,1 and 0.001, 0.10, and 0.16 g ethanol g biomass,1 h,1 for S. cerevisiae TMB 3399, TMB 3400, and P. stipitis CBS 6054, respectively. The xylitol yield under oxygen-limited and anaerobic conditions was two-fold higher for S. cerevisiae TMB 3399 than for TMB 3400, but the glycerol yield was higher for TMB 3400. The specific activity, in U mg protein,1, was higher for XDH than for XR in both S. cerevisiae TMB 3399 and TMB 3400, while P. stipitis CBS 6054 showed the opposite relation. S. cerevisiae TMB 3400 displayed higher specific XR, XDH and XK activities than TMB 3399. Hence, we have demonstrated that a combination of metabolic engineering and random mutagenesis was successful to generate a superior, xylose-utilizing S. cerevisiae, and uncovered distinctive physiological properties of the mutant. [source]

Modelling the growth of Weissella cibaria as a function of fermentation conditions

A. Ricciardi
Abstract Aims:, To investigate the effect of pH, water activity (aw) and temperature on the growth of Weissella cibaria DBPZ1006, a lactic acid bacterium isolated from sourdoughs. Methods and Results:, The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (40,80), aw (0935,0994) and temperature (10,45C) in a rich medium. The growth curve parameters (lag time, growth rate and asymptote) were estimated using the dynamic model of Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int J Food Microbiol23, 277,294). The effect of pH, aw and temperature on maximum specific growth rate (,max) were estimated by fitting a cardinal model. ,max under optimal conditions (pH = 66, aw = 0994, T = 363C) was estimated to be 093 h,1. Minimum and maximum estimated pH and temperature for growth were 36 and 815, and 90C and 478C, respectively, while minimum aw was 0918 (equivalent to 122% w/v NaCl). Conclusions:,Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread. Significance and Impact of the Study:, This is the first study reporting the modelling of the growth of W. cibaria, a species that is increasingly being used as a starter in sourdough and vegetable fermentations. [source]

Fermentation of enzymatic hydrolysates from olive stones by Pachysolen tannophilus

Manuel Cuevas
Abstract BACKGROUND: Olive stones were pretreated with liquid hot water (LHW or autohydrolysis) at maximum temperatures between 175 and 225 C (severity factors, logR0, between 2.73 and 4.39) to be subjected (both liquid and solid components) afterwards to enzymatic hydrolysis with cellulases from Trichoderma viride. Ethanol fermentation of hydrolysates was performed with the non-traditional yeast Pachysolen tannophilus ATCC 32691. RESULTS: After the enzymatic step, yields of hemicellulose solubilization reached 100%, while the cellulose was only partially hydrolysed (23%, logR0 = 4.39). The maximum yields in total reducing sugars and acetic acid, at the upper end of the severity range, was close to 0.25 and 0.04 g g,1 dry stone, respectively. During the fermentation stage, the increase in R0 reduced the maximum specific growth rate, biomass productivity, and overall biomass yield. The overall yields of ethanol and xylitol ranged, respectively, from 0.18 to 0.25 g g,1 and from 0.01 to 0.13 g g,1. CONCLUSIONS: The results demonstrate the possibility of producing ethanol from olive stones, making use of the cellulose and hemicellulose fraction of the waste. It was confirmed that the overall yield in xylitol strongly depended on severity factor, while the overall yield in ethanol remained practically constant for all the pretreatment conditions tested. Copyright 2008 Society of Chemical Industry [source]

Biodegradation kinetics of benzene, methyl tert -butyl ether, and toluene as a substrate under various substrate concentrations

Chi-Wen Lin
Abstract Owing to the complexity of conventional methods and shortcomings in determining kinetic parameters, a convenient approach using the nonlinear regression analysis of Monod or Haldane type nonlinear equations is presented. This method has been proven to provide accurate estimates of kinetic parameters. The major work in this study consisted of the testing of aromatic compound-degrading cultures in batch experiments for the biodegradation of benzene, methyl tert -butyl ether (MTBE), and toluene. Additionally, batch growth data of three pure cultures (i.e., Pseudomonas aeruginosa YAMT421, Ralstonia sp. YABE411 and Pseudomonas sp. YATO411) isolated from an industrial petrochemical wastewater treatment plant under aerobic conditions were assessed with the nonlinear regression technique and with a trial-and-error procedure to determine the kinetic parameters. The growth rates of MTBE-, benzene-, and toluene-degrading cultures on MTBE, benzene, and toluene were significant. Monod's model was a good fit for MTBE, benzene and toluene at low substrate concentrations. In contrast, Haldane's equation fitted well in substrate inhibition concentration. Monod and Haldane's expressions were found to describe the results of these experiments well, with fitting values higher than 98%. The kinetic parameters, including a maximum specific growth rate (m), a half-saturation constant (Ks), and an inhibition constant (Ki), were given. Copyright 2007 Society of Chemical Industry [source]

The fermentation of mixtures of D -glucose and D -xylose by Candida shehatae, Pichia stipitis or Pachysolen tannophilus to produce ethanol

Sebastin Snchez
Abstract The fermentation of mixtures of D -glucose and D -xylose by three non-traditional yeasts: Candida shehatae (ATCC 34887), Pachysolen tannophilus (ATCC 32691) and Pichia stipitis (ATCC 58376) have been studied to determine the optimal strain and initial culture conditions for the efficient production of ethanol. The comparison was made on the basis of maximum specific growth rate (m), biomass productivity, the specific rates of total substrate consumption (qs) and ethanol production (qE) and the overall yields of ethanol and xylitol. All the experiments were performed in stirred-tank batch reactors at a temperature of 30,C. The initial pH of the culture medium was 4.5. The highest values of m (above 0.5,h,1) were obtained with P stipitis in cultures containing high concentrations of D -xylose. All three yeasts consumed the two monosaccharides in sequence, beginning with D -glucose. The values of qs diminished during the course of each experiment with all of the yeasts. The highest values of the specific rates of total substrate consumption and ethanol production were obtained with C shehatae (for t,=,10,h, qs and qE were above 5,g,g,1,h,1 and 2,g,g,1,h,1, respectively), although the highest overall ethanol yields were fairly similar with all three yeasts, at around 0.4,g,g,1. 2002 Society of Chemical Industry [source]

Sensitivity analysis in oxidation ditch modelling: the effect of variations in stoichiometric, kinetic and operating parameters on the performance indices

A Abusam
Abstract This paper demonstrates the application of the factorial sensitivity analysis methodology in studying the influence of variations in stoichiometric, kinetic and operating parameters on the performance indices of an oxidation ditch simulation model (benchmark). Factorial sensitivity analysis investigates the sensitivities in a region rather than in a point. Hence, it has the advantage of giving more information about parameter interactions (non-linearity). Short-term results obtained have shown the following. The index AE is not significantly affected by variations in the value of parameters of the activated sludge model (ASM) No 1. The index TSP is greatly influence by heterotrophic yield (YH), heterotrophic decay (bH) and specific hydrolysis (kh) and the index EQ is dominated by YH, Monod coefficient (KS), bH, kh, anoxic condition correction factors (,g, ,h), hydrolysis half-saturation coefficient (KX), autotrophs maximum specific growth rate (A) and ammonia half-saturation coefficient (KNH). Furthermore, the index EQ has been shown to be very sensitive to parameter interactions, at certain regions. 2001 Society of Chemical Industry [source]


T. Alwyn
Marine phytoplankton and macroalgae acquire important resources, such as inorganic nitrogen, from the surrounding seawater by uptake across their entire surface area. Rates of ammonium and nitrate uptake per unit surface area were remarkably similar for both marine phytoplankton and macroalgae at low external concentrations. At an external concentration of 1 ,M, the mean rate of nitrogen uptake was 102 nmolcm,2h,1 (n=36). There was a strong negative relationship between log surface area:volume (SA:V) quotient and log nitrogen content per cm2 of surface (slope=,0.77), but a positive relationship between log SA:V and log maximum specific growth rate (,max; slope=0.46). There was a strong negative relationship between log SA:V and log measured rate of ammonium assimilation per cm2 of surface, but the slope (,0.49) was steeper than that required to sustain ,max (,0.31). Calculated rates of ammonium assimilation required to sustain growth rates measured in natural populations were similar for both marine phytoplankton and macroalgae with an overall mean of 6.21.4 nmolcm,2h,1 (n=15). These values were similar to maximum rates of ammonium assimilation in phytoplankton with high SA:V, but the values for algae with low SA:V were substantially less than the maximum rate of ammonium assimilation. This suggests that the growth rates of both marine phytoplankton and macroalgae in nature are often constrained by rates of uptake and assimilation of nutrients per cm2 surface area. [source]

Process optimization of the integrated synthesis and secretion of ectoine and hydroxyectoine under hyper/hypo-osmotic stress

C. Fallet
Abstract The synthesis and secretion of the industrial relevant compatible solutes ectoine and hydroxyectoine using the halophile bacterium Chromohalobacter salexigens were studied and optimized. For this purpose, a cascade of two continuously operated bioreactors was used. In the first bioreactor, cells were grown under constant hyperosmotic conditions and thermal stress driving the cells to accumulate large amounts of ectoines. To enhance the overall productivity, high cell densities up to 61,g,L,1 were achieved using a cross-flow ultrafiltration connected to the first bioreactor. In the coupled second bioreactor the concentrated cell broth was subjected to an osmotic and thermal down-shock by addition of fresh distilled water. Under these conditions, the cells are forced to secrete the accumulated intracellular ectoines into the medium to avoid bursting. The cultivation conditions in the first bioreactor were optimized with respect to growth temperature and medium salinity to reach the highest synthesis (productivity); the second bioreactor was optimized using a multi-objective approach to attain maximal ectoine secretion with simultaneous minimization of cell death and product dilution caused by the osmotic and thermal down-shock. Depending on the cultivation conditions, intracellular ectoine and hydroxyectoine contents up to 540 and 400,mg per g cell dry weight, respectively, were attained. With a maximum specific growth rate of 0.3,h,1 in defined medium, productivities of approximately 2.1,g,L,1,h,1 secreted ectoines in continuous operation were reached. Biotechnol. Bioeng. 2010;107: 124,133. 2010 Wiley Periodicals, Inc. [source]

Strategies to enhance cell growth and achieve high-level oil production of a Chlorella vulgaris isolate

Chun-Yen Chen
Abstract The autotrophic growth of an oil-rich indigenous microalgal isolate, identified as Chlorella vulgaris CC, was promoted by using engineering strategies to obtain the microalgal oil for biodiesel synthesis. Illumination with a light/dark cycle of 14/10 (i.e., 14 h light-on and 10 h light-off) resulted in a high overall oil production rate (voil) of 9.78 mg/L/day and a high electricity conversion efficiency (Ec) of 23.7 mg cell/kw h. When using a NaHCO3 concentration of 1,500 mg/L as carbon source, the voil and Ec were maximal at 100 mg/L/day and 128 mg/kw h, respectively. A Monod type model was used to describe the microalgal growth kinetics with an estimated maximum specific growth rate (,max) of 0.605 day,1 and a half saturation coefficient (Ks) of 124.9 mg/L. An optimal nitrogen source (KNO3) concentration of 625 mg/L could further enhance the microalgal biomass and oil production, leading to a nearly 6.19 fold increase in voil value. 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source]

Modeling and Optimization of Photosynthetic Hydrogen Gas Production by Green Alga Chlamydomonas reinhardtii in Sulfur-Deprived Circumstance

Ji Hye Jo
Biological hydrogen production by the green alga Chlamydomonas reinhardtii under sulfur-deprived conditions has attracted great interest due to the fundamental and practical importance of the process. The photosynthetic hydrogen production rate is dependent on various factors such as strain type, nutrient composition, temperature, pH, and light intensity. In this study, physicochemical factors affecting biological hydrogen production by C. reinhardtii were evaluated with response surface methodology (RSM). First, the maximum specific growth rate of the alga associated with simultaneous changes of ammonium, phosphate, and sulfate concentrations in the culture medium were investigated. The optimum conditions were determined as NH4+ 8.00 mM, PO43, 1.11 mM, and SO42, 0.79 mM in Tris-acetate-phosphate (TAP) medium. The maximum specific growth rate with the optimum nutrient concentrations was 0.0373 h,1. Then, the hydrogen production rate of C. reinhardtii under sulfur-deprivation conditions was investigated by simultaneously changing two nutrient concentrations and pH in the medium. The maximum hydrogen production was 2.152 mL of H2 for a 10-mL culture of alga with density of 6 106 cells mL,1 for 96 h under conditions of NH4+ 9.20 mM, PO43, 2.09 mM, and pH 7.00. The obtained hydrogen production rate was approximately 1.55 times higher than that with the typical TAP medium under sulfur deficiency. [source]

Kinetic Modeling of the Autotrophic Growth of Pavlova lutheri: Study of the Combined Influence of Light and Temperature

Ana P. Carvalho
The optimization and control of biochemical processes require the previous establishment of mathematical models that can describe the effect of process variables on their actual kinetics. Environmental temperature is a modulating factor to which the algal cells respond continuously by adjusting their rates of cellular reactions, their nutritional requirements, and, consequently, their biomass composition. Light intensity is an exhaustible resource, indispensable to autotrophic organisms. The effects of light intensity and temperature on growth of the microalga Pavlova lutheri, which have hardly been considered to date in a simultaneous fashion, were experimentally assessed using a factorial experimental design; in this way, the effects of each variable independently and their interactions could be quantified, using maximum biomass (Xmax) or maximum specific growth rate (,max) as objective functions. The preliminary results produced indicated that light intensity plays a more important role on ,max than temperature; in the case of Xmax, both temperature and, to a lesser extent, light intensity do apparently play a role. The highest values of Xmax were associated with low temperatures and high light intensities; a similar behavior could be observed for ,max concerning light intensity, although the dependency on temperature did not seem to be as important. A more complex mechanistic model was then postulated, incorporating light and temperature as input variables, which was successfully fitted to the experimental data generated during batch cultivation of P. lutheri. [source]

Modelling the combined effect of temperature, pH and aw on the growth rate of Monascus ruber, a heat-resistant fungus isolated from green table olives

E.Z. Panagou
Abstract Aims: Growth modes predicting the effect of pH (35,50), NaCl (2,10%), i.e. aw (0937,0970) and temperature (20,40C) on the colony growth rate of Monascus ruber, a fungus isolated from thermally-processed olives of the Conservolea variety, were developed on a solid culture medium. Methods and Results: Fungal growth was measured as colony diameter on a daily basis. The primary predictive model of Baranyi was used to fit the growth data and estimate the maximum specific growth rates. Combined secondary predictive models were developed and comparatively evaluated based on polynomial, Davey, gamma concept and Rosso equations. The data-set was fitted successfully in all models. However, models with biological interpretable parameters (gamma concept and Rosso equation) were highly rated compared with the polynomial equation and Davey model and gave realistic cardinal pHs, temperatures and aw. Conclusions: The combined effect of temperature, pH and aw on growth responses of M. ruber could be satisfactorily predicted under the current experimental conditions, and the models examined could serve as tools for this purpose. Significance and Impact of the Study: The results can be successfully employed by the industry to predict the extent of fungal growth on table olives. [source]

Dynamic Predictive Model for Growth of Salmonella Enteritidis in Egg Yolk

V. Gumudavelli
ABSTRACT:,Salmonella Enteritidis (SE) contamination of poultry eggs is a major human health concern worldwide. The risk of SE from shell eggs can be significantly reduced through rapid cooling of eggs after they are laid and their storage under safe temperature conditions. Predictive models for the growth of SE in egg yolk under varying ambient temperature conditions (dynamic) were developed. The growth of SE in egg yolk under several isothermal conditions (10, 15, 20, 25, 30, 35, 37, 39, 41, and 43 C) was determined. The Baranyi model, a primary model, was fitted with growth data for each temperature and corresponding maximum specific growth rates were estimated. Root mean squared error (RMSE) values were less than 0.44 log10 CFU/g and pseudo- R2 values were greater than 0.98 for the primary model fitting. For developing the secondary model, the estimated maximum specific growth rates were then modeled as a function of temperature using the modified Ratkowsky's equation. The RMSE and pseudo- R2 were 0.05/h and 0.99, respectively. A dynamic model was developed by integrating the primary and secondary models and solving it numerically using the 4th-order Runge,Kutta method to predict the growth of SE in egg yolk under varying temperature conditions. The integrated dynamic model was then validated with 4 temperature profiles (varying) such as linear heating, exponential heating, exponential cooling, and sinusoidal temperatures. The predicted values agreed well with the observed growth data with RMSE values less than 0.29 log10 CFU/g. The developed dynamic model can predict the growth SE in egg yolk under varying temperature profiles. [source]