Monod Constant Research Articles

A simple thermodynamic approach for derivation of a general Monod equation for microbial growth

The Monod equation has been widely applied to describe microbial growth, but it has no any mechanistic basis. Based on the thermodynamics of microbial growth process, a general model for microbial growth was developed. The constants involved in the present model were defined with clear physical meanings. The model derived can be reduced to the Monod equation, Grau equation and Hill or Moser equation. Compared to the Michaelis–Menten constant with the equilibrium thermodynamic characteristics, it was shown that the Monod constant ( K s) has non-equilibrium thermodynamic characteristics.

Phenolic removal in olive oil mill wastewater using loofah-immobilized Phanerochaete chrysosporium

Olive oil mill wastewater (OMW) has a high organic load, and this is a serious concern of the olive industry. Conventional biological wastewater treatments, despite their simplicity and suitable performance are ineffective for OMW treatment since phenolics possess antimicrobial activity. In order to carry out a proper treatment of OMW, use of a microorganism able to degrade the phenolics is thus necessary. In this study the ability of Phanerochaete chrysosporium to degrade the phenolic compounds of OMW and to decrease the chemical oxygen demand (COD) using cells immobilized on loofah was examined. The basal mineral salt solution along with glucose, ammonium sulfate and yeast extract was used to dilute the OMW appropriately. The fungus did not grow on the concentrated OMW. The extent of removal in this bio-treatment, of total phenols (TP) and the COD were 90 and 50%, respectively, while the color and aromaticity decreased by 60 and 95%, respectively. The kinetic behavior of the loofah-immobilized fungus was found to follow the Monod equation. The maximum growth rate μmax was 0.045 h−1 while the Monod constant based on the consumed TP and COD were (mg/l) 370 and 6900, respectively.

Determination of Growth and Glycerol Production Kinetics of a Wine Yeast Strain Saccharomyces cerevisiae Kalecik 1 in Different Substrate Media

Glycerol has been known as an important by-product of wine fermentations improving the sensory quality of wine. This study was carried out with an endogenic wine yeast strain Saccharomyces cerevisiae Kalecik 1. The kinetics of growth and glycerol biosynthesis were analysed at various initial concentrations of glucose, fructose, and sucrose in a batch system. Depending on the determined values of Monod constants, glucose (K s = 28.09 g/l) was found as the most suitable substrate for the yeast growth. Initial glucose, fructose and sucrose concentrations necessary for maximum specific yeast growth rate were determined as 175 g, 100 l, and 200 g/l, respectively. The yeast produced glycerol at very high concentrations in fructose medium. Fructose was determined as the most suitable substrate for glycerol production while the strain showed low tendency to use it for growth. S. cerevisiae Kalecik 1 could not produce glycerol below 200 g/l initial sucrose concentration. When natural white grape juice was used as fermentation medium, maximum glycerol concentration and dry weight of the yeast were determined as 9.3 g/l and 11.8 g/l, respectively.

Kinetics of Bifidobacterium longum ATCC 15707 fermentations: effect of the dilution rate and carbon source

The effect of the dilution rate on biomass and product synthesis in fermentations of glucose, fructose and a commercial mixture of fructooligosaccharides (FOS) by Bifidobacterium longum ATCC 15707 was studied. Kinetic parameters (maximum specific growth rate, Monod constant, maintenance, and yield coefficients) in the mathematical model of the fermentation were estimated from experimental data. In the FOS mixture fermentations, approximately 12% of the total reducing sugars (mainly fructose) in the feed were not metabolized by the bacterium. In fermentations of fructose and the FOS mixture, biomass concentration increased as the dilution rate increased and, once maximum values were reached [3.90 (D=0.20 h(-1)) and 2.54 g l(-1) (D=0.15 h(-1)), respectively], decreased rapidly as the culture was washed out. Formic acid was detected at low dilution rates in glucose and fructose fermentations. The main products in fermentations of the three carbon sources were lactic and acetic acids. Average values of the molar ratio between acetic and lactic acids of 1.18, 1.21 and 0.83 mol mol(-1) were obtained in glucose, fructose and FOS mixture fermentations, respectively. In batch fermentations carried out without pH control this molar ratio was lower than 1.5 only when fructose was used as the carbon source.

Photobiological Hydrogen Production from Synthesis Gas: Carbon Sources, KL a and Kinetics Evaluation

AbstractPhoto‐evolution of hydrogen from synthesis gas using Rhodospirillum rubrum was studied in batch fermentation. Culture of R. rubrum was initially grown on malate, also with various initial concentrations of acetate and synthesis gas. The synthesis gas was a mixture of H2, CO and CO2. It was found that the doubling time of bacterium on 2.5 g/l of malate, and 2.5 g/l and 6 g/l of acetate were 8.4, 31.8, and 68.6 h, respectively. The growth of R. rubrum was not significant at high concentration of acetate. The cell density of microbe was 0.3 g/l on 2.5 g/l malate for incubation period of 5 days. The cell concentrations of 1.4 and 0.41 g/l were obtained in 2.5 and 6 g/l of acetate, respectively for duration of 5 days. Inhibition of substrate was clearly observed on cell yield and hydrogen production with high concentration of acetate. Maximum hydrogen production (1.8 mmol/l) was obtained when R. rubrum was grown on 2.5 g/l of acetate. Effect of agitation rate was carried out and it was found that more hydrogen production (1.8 mmol) was achieved at 250 rpm. Mass transfer and kinetic studies were performed on 2.5 g/l of acetate. Maximum specific growth rate (m̈m) and Monod constant (KH) were obtained at 9.8 h−1 and 0.14 atm, respectively. No substrate inhibition occurred at CO concentration of 0.56 atm.

Effects of different substrates on growth and glycerol production kinetics of a wine yeast strain Saccharomyces cerevisiae Narince 3

Glycerol, is important industrial product that can be produced using osmophilic yeasts. A study was carried out to determine the effects of glucose, fructose, and sucrose on growth and glycerol production kinetics of a wine yeast strain Saccharomyces cerevisiae Narince 3 in a batch system. Depending on the determined values of Monod constants, sucrose ( K s=44.53 g/l) was the most suitable substrate for yeast growth. Initial glucose, fructose and sucrose concentrations necessary for maximum specific yeast growth rate were 125, 175, and 200 g/l, respectively. The glycerol production rate was highest in fructose medium and reached a maximum level in the medium of 350 g/l of initial fructose concentration. In glucose medium, optimal glycerol production was observed at 300 g/l initial glucose concentration and at 400 g/l initial sucrose concentration in medium containing sucrose. In grape juice medium, maximum glycerol concentration and dry weight were 14.1 and 8.0 g/l, respectively.

A Thermodynamic Interpretation of the Monod Equation

The Monod equation for microbial growth is purely empirical, and the theoretical basis of this model stays unclear. Similar to any chemical reactions, overall microbial growth process is dependent upon the changes in free energy. This study showed that the Monod equation could be interpreted in a thermodynamic sense very well. It was probably for the first time demonstrated that the Monod constant ( K(s)) was inversely related to the equilibrium constant of the overall microbial growth process.

Kinetics and mass-transfer phenomena in anaerobic granular sludge.

The kinetic properties of acetate-degrading methanogenic granular sludge of different mean diameters were assessed at different up-flow velocities (V(up)). Using this approach, the influence of internal and external mass transfer could be estimated. First, the apparent Monod constant (K(S)) for each data set was calculated by means of a curve-fitting procedure. The experimental results revealed that variations in the V(up) did not affect the apparent K(S)-value, indicating that external mass-transport resistance normally can be neglected. With regard to the granule size, a clear increase in K(S) was found at increasing granule diameters. The experimental data were further used to validate a dynamic mathematical biofilm model. The biofilm model was able to describe reaction-diffusion kinetics in anaerobic granules, using a single value for the effective diffusion coefficient in the granules. This suggests that biogas formation did not influence the diffusion-rates in the granular biomass.

Growth kinetics of the filamentous microorganism Sphaerotilus natans in a model system of a food industry wastewater

Bulking by Sphaerotilus natans has been attributed to several factors such as low dissolved oxygen in the aeration basin, wastes with high C:N ratios and phosphorus limitation; however, the occurrence of bulking has been reported in fruit, vegetable, meat and poultry wastewaters in which the ratio C:N is variable. Growth of S. natans was analyzed in a model system of a food industry wastewater (potato processing waste) that was characterized by HPLC determining that citric acid was the most important identified component. The effect of several carbon sources on S. natans growth was also studied; different C:N ratios were tested in a continuous culture system (chemostat). This strain grew in a mineral medium with citric acid as a sole carbon source, in spite of the contradictory results found in literature. Chemostat studies showed that the medium was carbon-limited when C:N ratios <19 mgCOD (mgN-NH 3) −1. Monod kinetic growth coefficients, determined for this strain in chemostat were: maximum specific growth rate, μ max=0.301 h −1; Monod constant, K S=4.6 mgCOD l −1; true biomass growth yield, Y T X/S=0.490 mgVSS (mgCOD) −1; endogenous decay rate, k d=0.011 h −1 and maintenance coefficient, m S=0.022 mgCOD (mgVSS) −1 h −1. The obtained parameters were compared with literature data and the effect of glucose and citric acid as carbon sources was discussed; these parameters are useful in modeling the growth of S. natans in potato processing wastewaters (or in other effluents under carbon-limiting conditions) especially when citrate is the main component and can be used to control filamentous bulking by metabolic or kinetic selection.

Physiology and taxonomy of Thiobacillus strain TJ330, which oxidizes carbon disulphide (CS2)

A bacterium (strain TJ330) capable of using carbon disulphide (CS2) as its sole energy source in an acidic environment was isolated from a peat biofilter used in experiments to remove CS2 and hydrogen sulphide (H2S) from air. Its physiology and taxonomy are described here. The strain oxidized CS2, H2S and elemental sulphur to sulphate chemolithotrophically. The rate of sulphate production was highest at pH 2. The maximum growth rate constant (micromax) using CS2 as a substrate was 3.9 x 10(-2) h(-1) (generation time 18 h) and the Monod constant (Ks) was 0.97-2.6 micromol l(-1) CS2 (74-198 microg l(-1)), corresponding to an equilibrium with 15-40 ppm CS2 in the headspace. The optimum growth temperature using elemental sulphur as a substrate was 28 degrees C. The strain bears morphological and physiological similarities to Thiobacillus thiooxidans, but the latter is incapable of oxidizing CS2. The strain TJ330 (DSM 8985) showed only 44.2 + 11.8% DNA homology with the type strain T. thiooxidans ATCC 19377, while its homology with T. ferrooxidans ATCC 23270 was 17.1 + 3.4%. The strain TJ 330 represents a high-affinity bacterium which can effectively remove low CS2 concentrations in an acid environment. These properties can be utilized in biotechnological purification applications.

Modelling the interactions between Lactobacillus curvatus and Enterobacter cloacae: I. Individual growth kinetics

Mixed cultures of Lactobacillus curvatus and Enterobacter cloacae were chosen as a model system to quantitatively study microbial interactions involved in food spoilage and food preservation. In this paper models were developed to predict the individual behaviour of L. curvatus and E. cloacae in pure suspension cultures as a function of the glucose and lactate concentration and the pH. In a second paper these models will be used to predict the moment of interaction in mixed suspension cultures and the cell concentrations at this moment. The effect of pH on the maximum specific growth rate could be described by a parabolic equation for L. curvatus and E. cloacae. E. cloacae is clearly more sensitive to a pH decrease than L. curvatus, as may be concluded from the theoretical minimum pH for growth of 5.6 for E. cloacae and 4.3 for L. curvatus. For both organisms no effect of glucose on the maximum specific growth rate could be detected and Monod kinetics with a low Monod constant was assumed. For L. curvatus the effect of lactate on the maximum specific growth rate at different initial pH values could be described by a linear relationship. For E. cloacae a slight effect of lactate on the maximum specific growth rate could only be detected at pH 7. However, this effect was negligible compared to the effect of the pH. For both organisms the lag time was modelled by the inverse of the specific growth rate. It can be concluded that, with regard to interactions between L. curvatus and E. cloacae, the pH is likely to be the most important factor in the case where L. curvatus is the dominant organism. Substrate limitation is likely to become important in the case where E. cloacae is the dominant organism or for media with a high buffer capacity.

Mathematical model for the biodegradation of VOCs in trickle bed biofilters

The objective of this work is to develop a fundamental mathematical model that describes the biodegradation of volatile organic compounds (VOCs) in gas phase trickle-bed biofilters, and to estimate the unknown model parameters. The mathematical model considers a three-phase system (biofilm, water, and gas phase), non-uniform bacterial population, and one limiting substrate. Two pilot-scale trickle-bed biofilters were operated to remove the VOC diethyl ether from a waste gas stream. Experimental results from this system were used to estimate the unknown parameters of the steady-state model: the maximum rate of substrate utilization μmXf/Y, the Monod constant, Ks, and the ether biofilm/water diffusivity ratio, rd. While the value of μmXf/Y was uniquely determined, the values of Ks and rd were highly correlated. High values of the Monod constant and the ether diffusivity in the biofilm gave similar predictions to those corresponding to low values of both parameters. Batch studies were used to estimate the value of Ks without mass transfer limitations showing that Ks &amp;lt; 1 mg/L=2.6 mg COD/L. Using this information and biofilter operating data the true values of Ks and rd were determined.

Mathematical model for the biodegradation of VOCs in trickle bed biofilterss

The objective of this work is to develop a fundamental mathematcal model that describes the biodegradation of volatile organic compounds (VOCs) in gas phase trickle-bed biofilters, and to estimate the unknown model parameters. The mathematical model considers a three-phase system (biofilm, water, and gas phase), non-uniform bacterial population, and one limuting substrate. Two pilot-scale trickle-bed biofilters were operated to remove the VOC diethyl ether from a waste gas stream. Experimental results from this system were used to estmate the unknown parameters of the steady-state model: the maximum rate of substrate utilization µmXf / Y, If. the Monod constant, Ks and the ether biofilm/water dlffusivity ratio. rd While the value of µmXf / Y was uniquely determined, the values of Ks, and rd, were highly correlated. High values of the Monod constant and the ether diffusivity in the biofilm gave similar predictions to those corresponding to low values of both parameters. Batch studies were used to estimate the value of Ks, without mass transfer limitations showing that Ks, < 1 mg/L=2.6 mg CODIL. Using this information and biofilter operating data the true values of Ks, and rd were determined.

Simultaneous utilization of glucose and D-xylose by Candida shehatae in a chemostat

The kinetics of biomass formation, D-xylose utilization, and mixed substrate utilization were determined in a chemostat using the yeast Candida shehatae. The maximum growth rate of C. shehatae grown aerobically on D-xylose was 0.42 h−1 and the Monod constant, Ks, was 0.06 g L−1. The biomass yield, Y{X/S}, ranged from 0.40 to 0.50 g g−1 over a dilution rate range of 0.2–0.3 h−1, when C. shehatae was grown on pure D-xylose. Mixtures of D-xylose and glucose (∼1 : 1) were simultaneously utilized over a dilution rate from 0.15 to 0.35 h−1 at pH 3.5 and 4.5, but pH 3.5 reduced μmax and reduced the dilution rate range over which D-xylose was utilized in the presence of glucose. At pH 4.5, μmax was not reduced with the mixed sugar feed and the overall or lumped Ks value was not significantly increased (0.058 g L−1vs 0.06 g L−1), when compared to a pure D-xylose feed. Kinetic data indicate that C. shehatae is an excellent candidate for chemostat production of value added products from renewable carbon sources, since simultaneous mixed substrate utilization was observed over a wide range of growth rates on a 1 : 1 mixture of glucose and D-xylose.

Growth kinetics ofPseudomonas putida G7 on naphthalene and occurrence of naphthalene toxicity during nutrient deprivation

The objectives of this work were (1) to demonstrate how the chemostat approach could be modified to allow determination of kinetic parameters for a sparingly soluble, volatile substrate such as naphthalene and (2) to examine the influence of the interactions of various nutrients on possible growth-inhibitory effects of naphthalene. Pseudomonas putida G7 was used as a model naphthalene-degrading microorganism. Naphthalene was found to be toxic to P. putida G7 in the absence of a nitrogen source or oxygen. The death rate of cells grown on minimal medium plus naphthalene and then exposed to naphthalene under anoxic conditions was higher than that observed under oxic conditions in the absence of a nitrogen source. The presence of necessary nutrients for the biodegradation of PAH compounds is indicated to be important for the survival of microorganisms that are capable of PAH degradation. The amounts of ammonia and oxygen necessary for naphthalene biodegradation and for suppression of naphthalene toxicity were calculated from growth yield coefficients. A chemostat culture of P. putida G7 using naphthalene as a carbon and energy source was accomplished by using a feed augmented with a methanol solution of naphthalene so as to provide sufficient growth to allow accurate evaluation of kinetic parameters. When naphthalene was the growth-limiting substrate, the degradation of naphthalene followed Monod kinetics. Maximum specific growth rate (micrometer) and Monod constant (Ks) were 0.627 +/- 0.007 h-1 and 0.234 +/- 0.0185 mg/L, respectively. The evaluation of biodegradation parameters will allow a mathematical model to be applied to predict the long-term behavior of PAH compounds in soil when combined with PAH transport parameters.

Mathematical model forPhaffia rhodozyma growth using peat hydrolysates as substrate

The potential of peat hydrolysates for the production of astaxanthin from Phaffia rhodozyma yeast biomass in continuous fermentation was studied. Chemostat fermentations of the yeast were performed using peat hydrolysates as substrate. Kinetic parameters were calculated for the growth of the yeast and the biomass productivity was determined using mathematical models. A low maximum specific growth rate (μ max = 0.08 h -1 ) and a high Monod constant (K s = 26.2 x 10 3 ) were obtained for this substrate. The low maintenance energy requirement found, 0020 g (gh) -1 , confirms the aerobic metabolism of the yeast with this substrate. Under selected conditions, a biomass productivity of 0.108 g (1h) -1 and an astaxanthin productivity of 0.046 mg (1h) -1 were obtained. The biomass produced had a high protein and astaxanthin content (490 ± 8 g kg -1 and 0.43 ± 0.07 g kg -1 , respectively), indicating that it can be used as a feed additive.

A Model Describing Pesticide Bioavailability and Biodegradation in Soil

AbstractA model is proposed for describing pesticide‐substrate bioavailability and rates of biodegradation in soil. The model accounts for sorption to soil surfaces, diffusion into the internal matrix of soil organic matter or aggregates, and microbial growth. Rates of sorption and diffusion are approximated by first‐order kinetics while microbial growth is approximated by Monod kinetics. Model verification was performed using 2,4‐D (2,4‐dichlorophenoxyacetic acid) degradation data from high and low organic matter soils inoculated with pure cultures of 2,4‐D degrading bacteria. Estimates of sorption, diffusion, and Monod constants were obtained sequentially by fitting the defining differential equations to the data using nonlinear regression techniques. Independent estimates of initial biomass (X0) and growth yield (Y) were required, although X0 could be approximated from the number of colony‐forming units assuming a bacterial weight of 0.1 pg cell−1. The model could account for the partitioning of 2,4‐D between soluble and sorbed phases and provided estimates of the Monod constants, µmax and KS, which were generally consistent with values previously determined in pure culture. In conjunction with pest toxicology data, the model may be useful in predicting the time between application and loss of efficacy (i.e., window of efficacy) for biodegradable pesticides.

Modeling of Degradation of Solutions Containing Nitrogen and Carbon Compounds in Aerated Submerged Fixed-Film (ASFF) Bioreactors

The biodegradation reaction rates of waste-water solutions containing nitrogen and carbon compounds were studied in an aerated submerged fixed film (ASFF) reactor with four compartments. A solution containing sucrose (carbon source) and ammonium chloride (nitrogen source) was considered in this study. The kinetic models considered in the analysis were the variable order model and the Monod model. Measurements and analysis were performed as a function of organic and hydraulic loading for the reactor. Analysis of the kinetic data was carried out in the first compartment and in the combined section of the reactor which included the second, third, and fourth compartments. The reaction order for carbon removal in the first compartment was found to vary over a range of 1–2 and drops to a range of 0.7–1.2 in the combined section. Lower reaction orders were obtained for nitrogen removal which varied from 0.6–1 in the first compartment and the combined section. Upon application of the Monod model for the two reactions, similar trends to those of the variable order model were obtained for carbon and nitrogen removal in both sections of the reactor. The calculated Monod constants for carbon removal were one to two orders of magnitudes larger than those for nitrogen removal. Measured removal rates of carbon in the first compartment were two orders of magnitudes higher than the nitrogen removal rates in the same compartment. However, the removal rates of both components are comparable in the combined section, especially at high feed flow rates. This behaviour was consistent with literature data on simultaneous removal of carbon and nitrogen compounds, where high concentrations of carbon resulted in severe reduction in the removal rates of nitrogen compounds.

Modelling of ethanol production by Saccharomyces cerevisiae from a glucose and maltose mixture

A model for ethanol production from a glucose-maltose mixture has been proposed, which includes a term representing the glucose repression effect on maltose consumption. The model parameters were estimated from batch experimental data. Results of sensitivity analysis on the Monod constants for glucose and maltose, and the repression constant, showed that ±10% changes in these three parameters caused no significant effect on data fitting.

The Monod equation and mass transfer

An alternative interpretation of the growth rate-substrate concentration dependence is presented. This is based on the assumption that the main factors affecting growth rate are transfer of substrate from the medium and the maximum growth velocity, which is that observed when no substrate limitations occur. This approach allows the approximate prediction of one of the two kinetic constants required, and may be of great use, especially for continuous cultures. It is the first attempt to provide a phenomenological explanation for the large variations observed in the values of the Monod constant, K(s), reported in the literature. (c) 1995 John Wiley & Sons, Inc.