Microbial Growth Kinetics Research Articles

The rotorfermentor. II. Application to ethanol fermentation

The kinetics of microbial growth and product formation are described as applied to the high cell concentration scheme of the rotorfermentor. A bench scale pilot plant was designed and built in order to demonstrate the operational feasibility of the rotorfermentor. The fermentation of glucose to ethanol by Saccharomyces cerevisiae ATCC 4126 was used. When the rotorfermentor was used with a glucose feed concentration of 104 g/liter almost 100% glucose utilization was obtained and the ethanol productivity rate was 27.3 g ethanol/liter hr which was found to be about 10 times greater than the ethanol productivity obtained from an ordinary continuous stirred tank (CST) fermentor. The ethanol experimental results obtained from the rotorfermentor and an ordinary CST fermentor were used as a basis to assess the economic feasibility of the rotorfermentor. The economics of an industrial scale ordinary CST fermentor with and without cell recycle is compared with a rotorfermentor unit for the same ethanol production throughput. For the process conditions considered in this case, calculations showed that the rotorfermentor may replace both a CST fermentor and cell centrifuge resulting in lower capital equipment costs and lower power consumption requirements.

Kinetics of algal transient phosphate uptake and the cell quota concept 1

Dissolved inorganic orthophosphate (P1) uptake rates (v) were determined as a function of total cell phosphorus content (Q) in P1 perturbed axenic batch cultures of Selenastrum capricornutum and Nostoc sp. The results showed an inverse relationship between v and Q for both organisms. These findings are used to relate the cell quota concept of nutrient limited, steady state microbial growth kinetics to nutrient uptake kinetics observed in perturbed batch cultures.

Bacterial growth kinetics in the completely mixed activated sludge treatment of fellmongery effluent

Fellmongery effluent was successfully treated (± 85% OA reduction) in a laboratory scale completely mixed activated sludge (CMAS) reactor with sludge recycle and controlled wasting. Varying the sludge age was found to have a significant effect on effluent quality. A mathematical model useful in the design and operation of effluent treatment plants was used to describe microbial growth in the treatment process. In the development of the model it is shown how a clear distinction must be made between the volatile suspended solids and the active volatile suspended solids for the model to accurately describe microbial growth kinetics.

Influence sur la cinetique biochimique de la concentration en carbone organique a l'entree d'un reacteur developpant une polyculture microbienne en melange parfait

Experiments were run in order to determine microbial growth kinetics of a mixed culture in a continuous stirred tank reactor using a multicomponent substrate. Analysis of the results indicated that effluent concentration does not depend only on the dilution rate but also on the concentration of substrate in the influent. A kinetic equation has been established using total organic carbon as a pollution indicator: k = k o ( S/ S + αS o )

On describing microbial growth kinetics from continuous culture data: Some general considerations, observations, and concepts

Analysis of continuous culture methodology suggests that this potentially powerful tool for kinetic analysis can be improved by minimizing several inherent shortcomings. Medium background substrates - organic carbon, phosphate, and manganese - were shown to dominate kinetic observations at concentrations below chemical detection methods. Reactor wall growth, culture size distribution changes, sample removal-induced steady state perturbations, and limiting substrate leakage from organisms are treated in terms of kinetic measurement errors. Large variations in maximal growth rates and substrate uptake rates found are attributed to experimental protocol-induced transient states. Relationships are presented for correcting limiting substrate concentrations for lability during sampling, contamination with unreacted medium, and background substrate effects. Analytical procedures are discussed for improved measurement of limiting substrate kinetics involving enzymes, isotopes, and material balance manipulation. Relaxation methods as applied to continuous culture are introduced as a means for isolating separate rate constants describing net substrate transport and for evaluating cellular metabolite leakage. Low velocity growth, multiple substrate metabolism, and endogenous metabolism are discussed along with measurements showing that 1-month generation times for aquatic microorganisms can be quite normal and that the kinetics are compatible withμg/liter limiting substrate concentrations. The concept of regarding growth kinetics as the sum of several net accumulation processes is suggested.

Slime Holdup, Influent BOD, and Mass Transfer in Trickling Filters

The performance of a trickling filter is described in terms of the kinetics of microbial growth, the slime holdup, the properties of the packing material, and the mass transfer characteristics of the liquid flow. Diffusional limitations in both the slime and the liquid phases, and the nonlinear dependence of the substrate uptake rate on both substrate concentration and slime thickness, have been taken into account. The appropriate analytical asymptotic expressions have been derived and the conditions under which they can be used have been identified quantitatively. The relationship between the present analysis and a number of empirical and “fundamental” models of trickling filter performance is explored.

Kinetics of substrate inhibition of exponential yeast growth

AbstractThis work concerns mathematical modeling of the rate of microbial growth on inhibitory levels of nutrients as affected by pH, concentration of the nutrients, temperature, cultivation method, and method of data analysis. Candida utilis (ATCC 9226) was grown with sodium acetate as growth‐limiting carbon and energy source in mineral salts medium in shake flask and continuous cultures to study inhibition by excess acetate. Differential shake flask cultures were grown at low yeast concentrations at temperatures (T) of 25 and 30°C, pH's between 5.5 and 7.0, and acetate concentrations (S) between 0.25 and 3.0% (w/v). Growth data were exponential with correlation coefficients greater than 0.995 in 49 of 56 experiments; the lowest correlation coefficient was 0.986. Specific growth rates (μ) determined by graphical methods showed only fair correlation with those determined by regression analysis. Both sets of specific growth rate data were grouped at constant T and pH and fitted to the three parameter equation, The improvement in use of the fitted equation instead of the mean value was significant with greater than 70% confidence in all (14 groups) and 90% confidence in only half of the data groups; the correlation does not improve with the increasing acetate inhibition at lower pH. Both defects in the model and insufficient data at each pH are responsible. A modified six parameters with hydrogen ion concentration(H+) as follows: Specific growth rates calculated with the six parameter equation matched observed values in all groups of isothermal data better than the means with greater than 99% confidence. The six parameter model adequately represents effects of acetate and hydrogen ion concentrations under constant or slowly changing environmental conditions and balanced growth; although better models probably exist. Thus steady‐stste and transient continuous culture experiments agreed with many published growth yields, but specific growth rates could only be predicted qualitatively from the model fit to the shake flask data. The data and present models could be incorporated into published models for transient growth at low nutrient concentrations to correlate and perhaps predict microbial growth kinetics over a much wider range of growth conditions than now possible.

A two-state microbial growth kinetics model

This study considers the possibility that dispersed bacteria and bacteria aggregated in floc possess different physiological states and that aggregation of dispersed cells to form floc particles is a reversible rate process. A suitable kinetic model of flocculation is proposed, in which the floc phase and dispersed phase bacteria exhibit different growth rates. Transient responses to changes in dilution rate and inlet concentration are investigated. Results are compared with experimental observations. Variation in observed yield factor and hysteresis of specific growth rate are observed.

Kinetics of Microbial Growth in Bulk Parenteral Solutions I. S. Faecalis and B. Subtilis in Dextrose-Saline and Hyperalimentation Solutions

Kinetics of Microbial Growth in Bulk Parenteral Solutions I. S. Faecalis and B. Subtilis in Dextrose-Saline and Hyperalimentation Solutions

Quantum Chemical Approach to Structure‐Activity Relationships of Tetracycline Antibiotics

Bacteriostatic activities for tetracyclines, determined in vitroby microbial growth kinetics, should be related to the perturbation energy, ΔEi, which characterizes the interaction between these antibiotics and their receptor substance. Quantum perturbation molecular orbital theory, combined with multiple‐regression techniques, are applied in gaining estimates of the relative variations in ΔEi for a family of tetracyclines which act in an identical way on a receptor region of unknown structure. The results of this theoretical approach are in good agreement with a number of independent observations relating to the bacteriostatic effects of tetracyclines and are consistent with the hypothesis that bacterial growth inhibition by tetracyclines is a consequence of an inhibition in protein synthesis due to the association of the antibiotic with a ribosomal site. The derived relationships between the bacteriostatic activities and the electronic structure of the tetracycline molecules implicate the oxygens at positions 10, 11, and 12 of the tetracycline nucleus as being intimately involved in leading to the bacteriostatic effects. This relationship also leads to satisfactory estimates for the inhibition rate constants of other tetracyclines, provided that specific effects such as intramolecular hydrogen bonding are taken into account. The effect of substituents on the electronic properties of the C6 and phenoldiketone tetracycline regions is to produce a gradation in the inhibitory properties of this family of antibiotics.

TEMPORAL AND VECTORIAL REACTIONS OF NITROGEN IN SOIL: A REVIEW

Some features of enzyme activities and microbial growth kinetics are reviewed and applied to sequential biochemical reactions in soil. Transformations of some soluble nitrogen compounds are discussed in terms of time of fluid flow downward in soil and a mathematical model is analyzed in such a way as to predict concentration-depth profiles of urea, ammonium, nitrite and nitrate. The intermediate compounds tend to reach maximal amounts in the profile whereas urea declines and nitrate, in the absence of denitrification, accumulates with depth. Although the model is general, it is limited to fallow soils or to laboratory soil columns. Nevertheless, the model suggests that much more needs to be learned about the influence of microenvironments on soil microbes and soil metabolism before any realistic analysis of dynamic profiles can be achieved.

Kinetics of microbial cell growth

AbstractAs a rate equation of microbial cell growth, the Monod equation is widely used. However, this equation cannot fully correspond to real courses of microbial cell growth in many batch cultivations. Especially, predicted values based on this equation do not agree with observed values in many continuous cultivations. In this paper, which introduces new concepts of critical concentration and coefficient of consumption activity, the growth rate equation which corresponds to the whole period including lag period is newly derived and characteristics of microbial cell growth in batch cultivation are clarified. Further, applying the new rate equation to continuous cultivation, a general equation with which to calculate cell concentration is derived and characteristics of microbial cell growth in continuous cultivation are clarified. The calculated values of cell concentration based on the new theory showed quite good agreement with the observed values in both batch and continuous cultivation.

Piston‐flow reactor model for continuous industrial fermentations

AbstractAlthough the piston‐flow (tubular) fermentor would provide operational difficulties, it is of significance for the analysis of mixing imperfections, for the analysis of a large number of stirredtank fermentors operated in series, and for the possibility of more efficient operation than the stirred tank. The basic kinetics of microbial growth are reviewed, noting that the reaction order varies during the course of reaction from autocatalytic first to ordinary first order; the equations describing effluent micro‐organism and limiting substrate concentrations for a stirred‐tank fermentor operated with recycle are reviewed. A rigorous analysis of the piston‐flow fermentor is given, for the first time, by means of a combination of the equations of microbial growth with a mathematical description of the hydraulic regime. A quantitative comparison is made between the two basic reactor types: the type of fermentor used depends on the objective of the process; if the objective is the reduction in effluent concentration of the limiting substrate, the piston‐flow fermentor provides more efficient operation. High recycle and concentration factors are of greater benefit to the piston‐flow unit, which becomes more efficient from the point of view of both objectives.

Kinetics of microbial growth and substrate consumption

A theoretical treatment of the heterogeneous reactions between microorganisms and substrate has been developed, taking into account the self-multiplying nature of enzyme systems. This treatment has been confirmed by experiments on batch cultures of baker's and alcohol yeasts and Escherichia coli. Substrate consumption is related to the quantity of microorganisms x and of substrate s as − ds dt = − ∂s ∂x · dx dt − ∂s ∂p · dp dt = κ.S = κ m.S · x s 1 K + x s where ϰ m and ϰ are the substrate consumption rate constant and the specific substrate consumption rate respectively, K a constant and p the primary product. When substrate is converted into cell material at rate y, the formula for microbial growth is dx dt = −y ds dt = μ · x = μ m · x · s x K + s x where μ m and μ are the growth rate constant and the specific growth rate respectively. When y = 0 or μ m = 0, substrate is catalytically consumed, forming enzyme whose quantity is proportional to the population density. The results here presented generalize the results of several previous workers.