Limiting Substrate Concentration Research Articles

Potential application of room temperature synthesized MIL-100(Fe) in enhancing methane production in microbial electrolysis Cells-Anaerobic digestion treating Protein-Rich wastewater

Microbial electrolysis cell-anaerobic digestion (MEC-AD) is an emerging technology for methane production. However, low substrate degradation efficiency remains a challenge when processing protein substrates. This study developed a MIL-100(Fe) carbon cloth anode to enhance methane production and substrate degradation in MEC-AD. The effects of MIL-100(Fe) prepared under hydrothermal (H-MIL-100(Fe)) and room temperature conditions (R-MIL-100(Fe)) were compared. Results indicated that H-MIL-100(Fe) and R-MIL-100(Fe) increased cumulative methane production by 16.01% and 14.99%, respectively compared to normal cloth, each influencing methane production through distinct mechanisms. Electrochemical characterization showed that H-MIL-100(Fe) enhanced the electrochemical performance more significantly due to the enrichment of Geotalea, with the oxidation current improved by 7.39-fold (R-MIL-100(Fe) increased it by only 2.95-fold) to promote growth of Methanobacterium. Metagenomic analysis revealed that R-MIL-100(Fe) tended to metabolize amino acids into methane rather than support cellular life activities, indicating its practicality under limited substrate concentration. In summary, R-MIL-100(Fe) shows greater potential for application due to its mild synthesis conditions and advantages in treating complex substrates.

Characterisation of Pseudomonas mosselii H6 for aerobic denitrification: stoichiometry and reaction kinetics

The application of aerobic denitrifying bacteria in biological nitrogen removal has been of great interest. However, the mechanism of nitrogen conversion by aerobic denitrifying bacteria is unclear due to the lack of stoichiometry and kinetic studies. Therefore, this study aimed to investigate the stoichiometry and kinetics of aerobic denitrification using Pseudomonas mosselii H6 as a model strain. The results showed that the stoichiometric equations of strain H6 under different nitrogen source conditions were obtained by nitrogen balance analysis; the concentrations of different limiting substrates were set and combined with the multi-substrate Monod kinetic equation to fit the half-saturation constants of COD, ammonia, nitrate and nitrite nitrogen for strain H6, which were 230.1008, 25.3435, 4.1009 and 23.4601 mg/L, respectively; based on the model of “two-step denitrification”, the numerical simulation of the growth and aerobic denitrification of strain H6 under different limiting substrate concentrations was carried out by using AQUASIM software to test the validity of stoichiometric coefficients and kinetic constants and perfect fitting results were obtained. These parameters will help to simulate the growth and denitrification performance of aerobic denitrifying bacteria and provide an experimental basis for further quantitatively elucidating the mechanism of action in the aerobic denitrification process.

Novel biodegradable two-dimensional vanadene augmented photoelectro-fenton process for cancer catalytic therapy

Fenton reaction-based chemodynamic therapy is hardly a self-sufficient cancer treatment, due to its stringent reaction conditions, limited substrate concentration, and negative feedback from the tumor microenvironment. Herein, we synthesized a novel two-dimensional (2D) vanadium-based nanosheets (Vanadene, V NSs) with polyvalent surfaces (VIV/VV), a very narrow band gap of 0.8 eV, and high biodegradability by a liquid-phase exfoliation strategy. The polyvalent surface endowed its multiple capabilities to modulate TME through GSH consumption and O2 production via VV and to catalyze a Fenton-like reaction to produce ·OH under a mild condition via VIV. In addition, efficient energy conversions including near-infrared (NIR)-thermal conversion (photothermal therapy, PTT) and NIR-electron conversion (photodynamic therapy, PDT) were ensured by the narrow band gap, in which NIR-thermal conversion enhanced the Fenton-like reaction activity through accelerating ionization while NIR-electron conversion catalyzed the conversion of O2 to ·O2− for further breaking redox homeostasis. Moreover, V NSs-based nanocatalyst can be slowly degraded into non-toxic species, enabling it to be innocuously eliminated from the body after completing tumor eradication by single drug injection and single NIR irradiation. Therefore, this study provides new insights into a universal nanoplatform for NIR-enhanced combination cancer therapy, highlighting the utility of 2D V NSs in the field of biomedicine.

GROWTH MODELS IN MICROBIAL ECOSYSTEMS - RESOURCE OR DENSITY DEPENDENCE?

This paper aims at discussing the two main modeling schemes that are used to describe dynamically the growth of microbial ecosystems, that are resource and density-dependent growth functions, respectively. Monod has been the first to hypothesize that this growth is, before all, an increasing saturated function of the main limiting substrate concentration. Contois assumed that the growth is not only a function of the substrate but also of the biomass density-itself, and thus the name « density-dependent ». In re examining their respective experiments (species used, conditions of experiments, mode of reactor functioning, measurement techniques), we try to understand the engines for a density-dependent phenomenon to appear. In particular, we refer to recent experiments where it was shown that density-dependent appeared as soon as the biomass structures into flocs or in the presence of filamentous bacteria even at relatively low concentrations. Based on this historical review of data, it is shown that density-dependent kinetics is not systematically a question of biomass density but rather related to its structure within the medium and to the mobility of microbial cells.

Acetate limitation selects Geobacter from mixed inoculum and reduces polysaccharide in electroactive biofilm

Bioelectrochemical systems (BESs) are widely investigated as a promising technology to recover bioenergy or synthesize value-added products from wastewaters. The performance of BES depends on the activity of electroactive biofilm (EAB). As the core of BES, it is still unclear how the EAB is formed from mixed inoculum, and how exoelectrogens compete with non-exoelectrogens. Here we confirmed that microbial community composition and the morphology of EAB on the electrode including the thickness and porosity of the biofilm are critical for the performance of BES, and these properties can be simply controlled by the substrate concentration during EAB formation. The EAB formed with 0.1 g/L of acetate (EAB-0.1) exhibited a 90% higher current density than that formed with 1.0 g/L acetate (EAB-1.0). EAB-0.1 had a 50% higher electroactivity per biomass and a 20% thinner thickness than EAB-1.0, which was partly due to the 54% decrease of insulative polysaccharide in biofilm. Limited acetate also imposed a selective pressure to enrich Geobacter up to 88% compared to 72% when acetate was abundant. Our findings demonstrate that a highly active EAB can be formed by limiting substrate concentration, providing a broader understanding of the EAB formation process, the ecology of interspecies competitions and potential applications for bioenergy recovery and trace toxicant detection in the future.

Achieving partial denitrification-anammox in biofilter for advanced wastewater treatment

Recently, partial denitrification (PDN) - anaerobic ammonium oxidation (anammox) process has been widely studied in activated sludge for nitrate wastewater treatment. However, achieving PDN-Anammox in biofilter for domestic wastewater treatment was never reported. In this study, two lab-scale PDN biofilter and Anammox biofilter were built up to treat simulated domestic wastewater. The results showed that stable nitrogen removal performance was kept with averaged effluent nitrogen of 10.2 mg/L. Stable nitrite accumulation performance was achieved with low abundance of nitrite reductase gene, while influent composition influenced nitrogen transformation pathway in PDN biofilter. When treating domestic wastewater, nitrification and partial denitrification led to the higher nitrite accumulation ratio of 75.4%. The percentage contribution of anammox biofilter was 74.6% for nitrogen removal, and Candidatus Brocadia was dominant genus. After long-term operation, limited substrate concentration caused interspecific competition among various anammox bacteria, leading to an increasing proportion of Candidatus Brocadia fulgida. PDN-Anammox biofilter is a feasible process to advanced wastewater treatment, which could save aeration consumption and carbon source addition, and reduce sludge production.

Biogas Production from Poultry Wastewater using Anaerobic Digester

Experimental work was carried out for the production of Biogas from poultry waste water. The Poultry waste was collected from farm near Nagercoil at Kanyakumari District. Batch anaerobic digester was designed for 20L capacity. The experiment was carried out for 36 days to monitor the performance. Various parameters like pH, TS, COD have checked for every 24hours. The Production of biogas was measured by water displacement method. The methane content was analyzed by gas chromatography test. Based on the experimental data, kinetics studies have done for various models like Line Weaver-Burk method, Eadie-Hofstee method, Hanes-Woolf method. The Eadie-Hofstee Method has provided better prediction than other method. These results thus indicate that, Eadie-Hofstee Method is best to identify the growth rate, substrate concentration and Limiting Substrate Concentration of the system. The sludge of the poultry wastewater and digester were characterized by SEM analysis. The imaging was done to determine the morphological structure of the sludge and to view the bacterial growth on the surface of the sludge.

Biodegradation of phenol by Isochrysis galbana screened from eight species of marine microalgae: growth kinetic models, enzyme analysis and biodegradation pathway

Isochrysis galbana MACC/H59 was screened from eight strains of marine microalgae to investigate its capability for phenol biodegradation. Batch incubation experiments were performed for 25 to 200 mg L−1 initial phenol concentrations. Five growth inhibitory kinetic models were used to fit the experimental data. The specific activities of phenol hydroxylase and catechol dioxygenase in I. galbana are measured. The results showed that phenol, at concentrations of less than 100 mg L−1, could be completely degraded in 4 days. The growth kinetics of I. galbana under different phenol concentrations were best fitted with a Yano model among five kinetics models tested. The values of substrate inhibition constant (117.59 mg L−1), limiting substrate concentration (183.90 mg L−1) and optimal substrate concentration (81.46 mg L−1) for phenol biodegradation of I. galbana were also obtained with the Yano model. The phenol biodegradation in I. galbana was mainly catalysed by intracellular enzymes. The ortho-pathway is significantly predominant over the meta-pathway in phenol metabolism in I. galbana. High concentrations of phenol significantly inhibited the activity of phenol hydroxylase, but had no obvious effect on catechol dioxygenase. Isochrysis galbana may be a suitable marine microalgal species for use in environmental restoration operations after accidental spills of phenol at sea.

Modeling the heterogeneous catalytic activity of a single nanoparticle using a first passage time distribution formalism

Metal nanoparticles are heterogeneous catalysts and have a multitude of non-equivalent, catalytic sites on the nanoparticle surface. The product dissociation step in such reaction schemes can follow multiple pathways. Proposed here for the first time is a completely analytical theoretical framework, based on the first passage time distribution, that incorporates the effect of heterogeneity in nanoparticle catalysis explicitly by considering multiple, non-equivalent catalytic sites on the nanoparticle surface. Our results show that in nanoparticle catalysis, the effect of dynamic disorder is manifested even at limiting substrate concentrations in contrast to an enzyme that has only one well-defined active site.

Identifying the Correct Biotransformation Model from Polychlorinated Biphenyl and Dioxin Dechlorination Batch Studies.

We performed Monte Carlo simulations of batch transformations of hydrophobic compounds using typical numbers of data points, extent of reaction, and measurement error, to identify the most appropriate biotransformation model to describe such data under different conditions. Highly hydrophobic compounds such as polychlorinated biphenyls (PCBs) and dioxins present special challenges for parameterization due to low environmental concentrations and slow biotransformation rates, which result in high sample variability, few samples, and limited substrate concentration range. Four models of varying complexity (zero-order, first-order, Monod, and Best) were fit to simulated data. Various combinations of initial concentration (S0), half saturation concentration (KS), maximum substrate utilization rate (qmax), measurement error, number of data points per batch run, and extent of biotransformation were simulated. One thousand Monte-Carlo runs were performed for each parameter combination, and AICc (Akaike's information criterion corrected for small numbers of data points) was used to determine the most appropriate model. Neither the Best model nor the zero-order model ever produced the lowest AICc for a majority of simulations under any combination of test conditions. With 10% measurement error, the first-order model always outperformed the others. In the case of 1% measurement error with 10 evenly-spaced data points, the Monod model was the better choice when S0>KS and the system was not mass transfer limited [Formula: see text] otherwise, the first-order model was indicated. S0 is constrained by the compound's aqueous solubility; therefore, for highly hydrophobic compounds such as PCBs or polychlorinated dibenzo-p-dioxins and dibenzofurans, a first-order model is likely to fit batch biotransformation data as well or better than a more complicated model.

Alternative substrate kinetics of Escherichia coli ribonuclease P: Determination of relative rate constants by internal competition

A single enzyme, RNase P, processes the 5′ ends of ptRNAs in cells and organelles that carry out tRNA biosynthesis. This substrate population includes over 80 different competing ptRNAs in Escherichia coli. While the reaction kinetics and molecular recognition of a few individual model substrates of bacterial RNase P have been well described, the competitive substrate kinetics of the enzyme are unexplored. To understand how different ptRNA substrates compete for processing by RNase P, we compared the steady state reaction kinetics of two ptRNAs that differ at sequences that are contacted by the enzyme. For both ptRNAs, substrate cleavage is fast relative to dissociation. As a consequence, V/K, the rate constant for the reaction at limiting substrate concentrations, reflects the substrate association step for both ptRNAs. Reactions containing two or more ptRNAs follow simple competitive alternative substrate kinetics in which the relative rates of processing are determined by ptRNA concentration and their V/K. The relative V/K values for eight different ptRNAs, that were selected to represent a range of structure variation, were determined by internal competition in reactions in which all eight substrates are present simultaneously. The results suggest that rates of ptRNA processing by RNase P are tuned for uniform specificity and consequently optimal coupling to precursor biosynthesis.

Alternative Substrate Kinetics of Escherichia coli Ribonuclease P: DETERMINATION OF RELATIVE RATE CONSTANTS BY INTERNAL COMPETITION

A single enzyme, ribonuclease P (RNase P), processes the 5' ends of tRNA precursors (ptRNA) in cells and organelles that carry out tRNA biosynthesis. This substrate population includes over 80 different competing ptRNAs in Escherichia coli. Although the reaction kinetics and molecular recognition of a few individual model substrates of bacterial RNase P have been well described, the competitive substrate kinetics of the enzyme are comparatively unexplored. To understand the factors that determine how different ptRNA substrates compete for processing by E. coli RNase P, we compared the steady state reaction kinetics of two ptRNAs that differ at sequences that are contacted by the enzyme. For both ptRNAs, substrate cleavage is fast relative to dissociation. As a consequence, V/K, the rate constant for the reaction at limiting substrate concentrations, reflects the substrate association step for both ptRNAs. Reactions containing two or more ptRNAs follow simple competitive alternative substrate kinetics in which the relative rates of processing are determined by ptRNA concentration and their V/K. The relative V/K values for eight different ptRNAs, which were selected to represent the range of structure variation at sites contacted by RNase P, were determined by internal competition in reactions in which all eight substrates were present simultaneously. The results reveal a relatively narrow range of V/K values, suggesting that rates of ptRNA processing by RNase P are tuned for uniform specificity and consequently optimal coupling to precursor biosynthesis.

Investigation of Shelf Life of Potency and Activity of the Lactobacilli Produced Bacteriocins Through Their Exposure to Various Physicochemical Stress Factors.

Three Lactobacilli strains, Lactobacillus casei NCIMB 11970, Lactobacillus plantarum NCIMB 8014, Lactobacillus lactis NCIMB 8586 have been used for the production of bacteriocins. Though, their production phase, their biochemical nature, their mode of activity even their genetic structure have been widely investigated, there are hardly any studies investigating their potency and activity in depth of time, in other words their shelf life under several physicochemical conditions that may occur during their production in large scale. As such, the effect of several factors influencing the activity and the potency of bacteriocins when produced in large scale was examined as due to bacteriocins peptide nature degradation or denaturation might occur, under extreme physicochemical conditions. During scale-up process, differences between the output data may occur, such as concerning biomass, metabolic by-products and limiting substrate concentrations. These may affect negatively the activity and the potency of the bacteriocins. For investigating these effects and minimizing them, numerous studies were conducted, which were related to the exact phase of the production of these substances, the effect of dilution and temperature changes. These studies could be used in order to minimize the scaling-up effect when decided to produce these peptides in large scale.

On the Reducible Character of Haldane-Radić Enzyme Kinetics to Conventional and Logistic Michaelis-Menten Models

The conceptual and practical issues regarding the reduction of the Haldane-Radić enzymic mechanism, specific for cholinesterase kinetics, to the consecrated or logistically modified Michaelis-Menten kinetics, specific for some mutant enzymes, are here clarified as due to the limited initial substrate concentration, through detailed initial rate and progress curve analysis, even when other classical conditions for such equivalence are not entirely fulfilled.

Feedback stabilization for a chemostat with delayed output

We apply basic tools of control theory to a chemostat model that describes the growth of one species of microorganisms that consume a limiting substrate. Under the assumption that available measurements of the model have fixed delay t>0, we design a family of feedback control laws with the objective of stabilizing the limiting substrate concentration in a fixed level. Effectiveness of this control problem is equivalent to global attractivity of a family of differential delay equations. We obtain sufficient conditions (upper bound for delay t>0 and properties of the feedback control) ensuring global attractivity and local stability. Illustrative examples are included.

Model and Kinetic Parameters Identification for Therapeutical Product Obtained According to the GMP Guidelines

The technological solutions were elaborated to achieve the design of the production flow with respect of the Good Manufacturing Practice (GMP) guidelines. To be in line with the GMP rules a fed-batch operation mode is be designed based on the batch modelling results. As the production rate of the microbial immunomodulator is associated with the biomass growth rate, it was required to study the bacterium growth kinetics in batch process. After the selection of the kinetic model based on several batches experimental data by using the analysis criteria - modelling error and estimation rule convergence, the limiting substrate concentration to be maintained during fed-batch cells exponential growth was determined as 115 - 125 mg/L. The batch bioprocess was performed in a Bioengineering AG bioreactor with a software based control of the main variables.

Analytic Solution to Steady-State Radial Diffusion of a Substrate with First-Order Reaction Kinetics in the Tissue of a Krogh's Cylinder

It is often useful to calculate the concentration profile for a substrate undergoing reaction in the tissue surrounding a capillary. In this paper, we consider a model geometry consisting of a long straight cylinder of tissue surrounding a capillary. Substrate diffuses radially out of the capillary through the tissue, with consumption of substrate in the tissue directly proportional to substrate concentration (i.e., first-order reaction kinetics). The model is extended to include the case where a cylinder of necrotic tissue surrounds a metabolically active inner tissue cylinder. A simple analytic solution is derived, and concentration profiles are generated for various combinations of parameters. Compared to the case where substrate consumption is independent of concentration, this model predicts much more rapid depletion of substrate near the capillary interface. This can have significant implications for the calculation of the hypoxic fraction (e.g., tissue with pO(2)<0.5-5 mmHg) when tumor oxygenation is modeled. The model also permits calculation of the limiting substrate concentration for cell viability when the reaction rate constant is known and vice versa.

Steady-state Kinetic Mechanism of PDK1

PDK1 catalyzes phosphorylation of Thr in the conserved activation loop region of a number of its downstream AGC kinase family members. In addition to the consensus sequence at the site of phosphorylation, a number of PDK1 substrates contain a PIF sequence (PDK1-interacting fragment), which binds and activates the kinase domain of PDK1 (PDK1(deltaPH)). To gain further insight to PIF-dependent catalysis, steady-state kinetic and inhibition studies were performed for His6-PDK1(deltaPH)-catalyzed phosphorylation of PDK1-Tide (Tide), which contains an extended "PIF" sequence C-terminal to the consensus sequence for PDK1 phosphorylation. In two-substrate kinetics, a large degree of negative binding synergism was observed to occur on formation of the active ternary complex (alphaKd(ATP) = 40 microM and alphaKd(Tide) = 80 microM) from individual transitory binary complexes (Kd(ATP) = 0.6 microM and Kd(Tide) = 1 microM). On varying ATP concentrations, the ADP product and the (T/E)-PDK1-Tide product analog (p'Tide) behaved as competitive and noncompetitive inhibitors, respectively; on varying Tide concentrations, ADP and p'Tide behaved as noncompetitive and competitive inhibitors, respectively. Also, negative binding synergism was associated with formation of dead-end inhibited ternary complexes. Time progress curves in pre-steady-state studies under "saturating" or kcat conditions showed (i) no burst or lag phenomena, (ii) no change in reaction velocity when adenosine 5'-O-(thiotriphosphate) was used as a phosphate donor, and (iii) no change in reaction velocity on increasing relative microviscosity (0 < or = eta/eta0 < or = 3). Taken together, PDK1-catalyzed trans-phosphorylation of PDK1-Tide approximates a Rapid Equilibrium Random Bi Bi system, where motions in the central ternary complex are largely rate-determining.

Intrinsic kinetics of continuous growth and ethanol production of a flocculating fusant yeast strain SPSC01

The intrinsic kinetics of continuous yeast cell growth and ethanol production for a self-flocculating fusant yeast strain SPSC01 was investigated by means of mechanically dispersing the flocs and correspondingly established floc size distribution on-line monitoring technique using the focused beam reflectance measurement system, through which the floc intra-particle mass transfer limitation was effectively eliminated, but its ethanol formation metabolism was not affected. Modified kinetic models were developed, which can be used to predict the continuous kinetic behaviors of SPSC01, especially when low dilution rates are applied and limiting substrate concentrations are undetectable and almost all kinetic models developed previously are failed in predicting corresponding kinetic behaviors. Both substrate and product inhibitions reported for freely suspended yeast cell ethanol production were also observed for SPSC01 when high gravity media were fed and relatively high levels of residual sugar and ethanol presented. Model parameters were evaluated through numerical calculation method and validated by experimental data mu = 0.584C(s)/0.155 + C(s) + C(2)(s)/160.7(1 -P/125)(3.68) + 0.004 for growth, nu = 1.998C(s)/0.427 + C(s) + C(2)(s)/366.7(1- P/125)(1.72) + 0.060 for ethanol production These intrinsic kinetic models can be further used to develop the observed kinetic models that quantitatively correlate the impact of the self-flocculating yeast cell size distributions on their apparent rates for yeast cell growth, substrate uptake and ethanol production and optimize the ethanol production process.

Impacts of yeast floc size distributions on their observed rates for substrate uptake and product formation

The focused beam reflectance measurement (FBRM) probe was directly inserted into a small fermentor with a working volume of 650 mL and the on-line monitoring technique for the size distribution of SPSC01, a self-flocculating yeast strain, was established. It was found that the floc size distribution could be characterized by its mode, M, which was further correlated by a power function with the stirring speed, r. Therefore, the designated floc size distributions were obtained through controlling the stirring speed. The batch fermentation times were significantly extended when the same levels of ethanol and biomass concentrations were reached, but the floc size distributions characterized by M increased from 100 to 600 μm. These experimental results indicated that the intra-particle mass transfer limitation existed for such a self-flocculating yeast ethanol fermentation system and the kinetics ought to be categorized into two different levels: intrinsic and observed. The impacts of the floc size distributions on the observed rates for glucose uptake and ethanol production were quantitatively investigated by manipulating the stirring speed so that the designated floc size distributions were achieved. The effectiveness factors, η S and η P for glucose uptake and ethanol production, respectively, were further evaluated. It was found that both the floc size distribution and the level of limiting substrate concentration affected η S and η P.