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Mixed Microbial Cultures (mixed + microbial_culture)
Selected AbstractsInfluence of heavy metals on microbial growth kinetics including lag time: Mathematical modeling and experimental verification,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2009S. Sevinç, engör Abstract Heavy metals can significantly affect the kinetics of substrate biodegradation and microbial growth, including lag times and specific growth rates. A model to describe microbial metabolic lag as a function of the history of substrate concentration has been previously described by Wood et al. (Water Resour Res 31:553,563) and Ginn (Water Resour Res 35:1395,1408). In the present study, this model is extended by including the effect of heavy metals on metabolic lag by developing an inhibitor-dependent functional to account for the metabolic state of the microorganisms. The concentration of the inhibiting metal is explicitly incorporated into the functional. The validity of the model is tested against experimental data on the effects of zinc on Pseudomonas species isolated from Lake Coeur d'Alene sediments, Idaho, USA, as well as the effects of nickel or cobalt on a mixed microbial culture collected from the aeration tank of a wastewater treatment plant in Athens, Greece. The simulations demonstrate the ability to incorporate the effect of metals on metabolism through lag, yield coefficient, and specific growth rates. The model includes growth limitation due to insufficient transfer of oxygen into the growth medium. [source] Experimental and neural model analysis of styrene removal from polluted air in a biofilterJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2009Eldon R. Rene Abstract BACKGROUND: Biofilters are efficient systems for treating malodorous emissions. The mechanism involved during pollutant transfer and subsequent biotransformation within a biofilm is a complex process. The use of artificial neural networks to model the performance of biofilters using easily measurable state variables appears to be an effective alternative to conventional phenomenological modelling. RESULTS: An artificial neural network model was used to predict the extent of styrene removal in a perlite-biofilter inoculated with a mixed microbial culture. After a 43 day biofilter acclimation period, styrene removal experiments were carried out by subjecting the bioreactor to different flow rates (0.15,0.9 m3 h,1) and concentrations (0.5,17.2 g m,3), that correspond to inlet loading rates up to 1390 g m,3 h,1. During the different phases of continuous biofilter operation, greater than 92% styrene removal was achievable for loading rates up to 250 g m,3 h,1. A back propagation neural network algorithm was applied to model and predict the removal efficiency (%) of this process using inlet concentration (g m,3) and unit flow (h,1) as input variables. The data points were divided into training (115 × 3) and testing set (42 × 3). The most reliable condition for the network was selected by a trial and error approach and by estimating the determination coefficient (R2) value (0.98) achieved during prediction of the testing set. CONCLUSION: The results showed that a simple neural network based model with a topology of 2,4,1 was able to efficiently predict the styrene removal performance in the biofilter. Through sensitivity analysis, the most influential input parameter affecting styrene removal was ascertained to be the flow rate. Copyright © 2009 Society of Chemical Industry [source] Factors controlling the carbon isotope fractionation of tetra- and trichloroethene during reductive dechlorination by Sulfurospirillum ssp. and Desulfitobacterium sp. strain PCE-SFEMS MICROBIOLOGY ECOLOGY, Issue 1 2007Danuta Cichocka Abstract Carbon stable isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE) was investigated during reductive dechlorination. Growing cells of Sulfurospirillum multivorans, Sulfurospirillum halorespirans, or Desulfitobacterium sp. strain PCE-S, the respective crude extracts and the abiotic reaction with cyanocobalamin (vitamin B12) were used. Fractionation of TCE (,C=1.0132,1.0187) by S. multivorans was more than one order of magnitude higher than values previously observed for tetrachloroethene (PCE) (,C=1.00042,1.0017). Similar differences in fractionation were observed during reductive dehalogenation by the close relative S. halorespirans with ,C=1.0046,1.032 and ,C=1.0187,1.0229 for PCE and TCE respectively. TCE carbon isotope fractionation (,C=1.0150) by the purified PCE-reductive dehalogenase from S. multivorans was more than one order of magnitude higher than fractionation of PCE (,C=1.0017). Carbon isotope fractionation of TCE by Desulfitobacterium sp. strain PCE-S (,C=1.0109,1.0122) as well as during the abiotic reaction with cyanocobalamin (,C=1.0154) was in a similar range to previously reported values for fractionation by mixed microbial cultures. In contrast with previous results with PCE, no effects due to rate limitations, uptake or transport of the substrate to the reactive site could be observed during TCE dechlorination. Our results show that prior to a mechanistic interpretation of stable isotope fractionation factors it has to be carefully verified how other factors such as uptake or transport affect the isotope fractionation during degradation experiments with microbial cultures. [source] Application of pure and mixed probiotic lactic acid bacteria and yeast cultures for oat fermentationJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 12 2005Associate Professor Dr Angel Angelov Abstract Fermentation of a prebiotic containing oat substrate with probiotic lactic acid bacteria and yeast strains is an intriguing approach for the development of new synbiotic functional products. This approach was applied in the present work by using pure and mixed microbial cultures to ferment a heat-treated oat mash. Results show that the strains studied were appropriate for oat fermentation and the process could be completed for 6,10 h depending on the strain. The viable cell counts achieved within this time were above the required levels of 106,107 cfu ml,1 for probiotic products. Both single lactic acid bacteria strains and mixed cultures of the same strains with yeast were found suitable for oat fermentation. However, the pure LAB cultures attributed better flavour and shelf life of the oat drinks. The content of the prebiotic oat component beta-glucan remained within 0.30,0.36% during fermentation and storage of the drinks obtained with each of the strains used. Thus, these products would contribute diet with the valuable functional properties of beta-glucan. Also, the viability of pure and mixed cultures in the oat products was good: levels of cell counts remained above the required numbers for probiotic products throughout the estimated shelf-life period. Copyright © 2005 Society of Chemical Industry [source] Influence of feeding strategies of mixed microbial cultures on the chemical composition and microstructure of copolyesters P(3HB-co-3HV) analyzed by NMR and statistical analysisMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2009G. Ivanova Abstract NMR spectroscopy was applied for quantitative and qualitative characterization of the chemical composition and microstructure of a series of poly(3-hydroxybutyrate- co -3-hydoxyvalerate) copolymers, P(3HB- co -3HV), synthesized by mixed microbial cultures at several different feeding strategies. The monomer sequence distribution of the bacterially synthesized P(3HB- co -3HV) was defined by analysis of their high-resolution 1D 13C NMR and 2D 1H/13C HSQC and 1H/13C HMBC NMR spectra. The results were verified by employment of statistical methods and suggest a block copolymer microstructure of the P(3HB- co -3HV) copolymers studied. Definitive distinction between block copolymers or a mixture of random copolymers could not be achieved. NMR spectral analysis indicates that the chemical composition and microstructure of the copolymers can be tuned by choosing a correct feeding strategy. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effect of the applied organic load rate on biodegradable polymer production by mixed microbial cultures in a sequencing batch reactorBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2006Davide Dionisi Abstract This article studies the operation of a new process for the production of biopolymers (polyhydroxyalkanoates, PHAs) at different applied organic load rates (OLRs). The process is based on the aerobic enrichment of activated sludge to obtain mixed cultures able to store PHAs at high rates and yields. A mixture of acetic, lactic, and propionic acids at different concentrations (in the range 8.5,31.25 gCOD/L) was fed every 2 h in a sequencing batch reactor (SBR). The resulting applied OLR was in the range 8.5,31.25 gCOD/L/day. Even though, as expected, the increase in the OLR caused an increase in biomass concentration (up to about 8.7 g COD/L), it also caused a relevant decrease of maximal polymer production rate. This decrease in polymer production rate was related to the different extent of "feast and famine" conditions, as function of the applied OLR and of the start-up conditions. As a consequence the best performance of the process was obtained at an intermediate OLR (20 gCOD/L/day) where both biomass productivity and PHA storage were high enough. However, at this high OLR the process was unstable and sudden decrease of performance was also observed. The sludge characterized by the highest PHA storage response was investigated by 16S rDNA clone library. The clone library contained sequences mostly from PHA producers (e.g., Alcaligenes and Comamonas genera); however many genera and among them, one of the dominant (Thauera), were never described before in relation to PHA storage response. © 2005 Wiley Periodicals, Inc. [source] On-line adaptive metabolic flux analysis: Application to PHB production by mixed microbial culturesBIOTECHNOLOGY PROGRESS, Issue 2 2009João Dias Abstract In this work, an algorithm for on-line adaptive metabolic flux analysis (MFA) is proposed and applied to polyhydroxybutyrate (PHB) production by mixed microbial cultures (MMC). In this process, population dynamics constitutes an important source of perturbation to MFA calculations because some stoichiometric and energetic parameters of the underlying metabolic network are continuously changing over time. The proposed algorithm is based on the application of the observer-based estimator (OBE) to the central MFA equation, whereby the role of the OBE is to force the accumulation of intracellular metabolites to converge to zero by adjusting the values of unknown network parameters. The algorithm was implemented in a reactor equipped with on-line analyses of dissolved oxygen and carbon dioxide through respirometric and titrimetric measurements. The oxygen and carbon dioxide fluxes were measured directly, whereas acetate, PHB, and sludge production fluxes were estimated indirectly using a projection of latent structures model calibrated a priori with off-line measurements. The algorithm was implemented in a way that the network parameters associated with biosynthesis were adjusted on-line. The algorithm proofed to converge exponentially with the steady state error always below 1 mmol/L. The estimated fluxes passed the consistency index test for experimental error variances as low as 1%. The comparison of measured and estimated respiratory coefficient and of the theoretical and estimated yield of sludge on acetate further confirmed the metabolic consistency of the parameters that were estimated on-line. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] | |||||||||||||