A kinetic model for microbial growth on liquid hydrocarbons

A kinetic model is presented to explain microbial growth using liquid n-alkanes as substrate. The model is based on the assumption that growth occurs on the soluble alkane and that the metabolite produced by the growing cells helps the dissolution of liquid alkanes in the aqueous medium. Growth curves based on that model fit well with growth data for batch and continuous culture reported by various authors. The model also explains the differences between the relative length of exponential and linear phases of growth reported earlier.     

A generalized kinetic model for the study of microbial growth

The following general equation is proposed to represent the kinetics of microbial growth documentclass{article}pagestyle{empty}begin{document}$$phi (dR/dt) + psi R + X = 0$$end{document}, where phi and psi depend on several parameters of the fermenting system. The values of phi and psi were calculated based on results obtained in a batch lactic acid fermentation, a batch cultivation of yeast on diesel oil, and a continuous cultivation of yeast on sugarcane molasses.     

Mechanistic model for microbial growth on hydrocarbons

Based on available information describing the transport and consumption of insoluble alkanes, a mechanistic model is proposed for microbial growth on hydrocarbons. The model describes the atypical growth kinetics observed, and has implications in the design of large scale equipment for single cell protein (SCP) manufacture from hydrocarbons. The model presents a framework for comparison of the previously published experimental kinetic data.     

A mathematical model for microbial growth under limitation by conservative substrates

A mathematical model is suggested for growth of microorganisms under limitation by “conservative” substrates such as inorganic ions or vitamins that are not broken down after uptake into the cells, but that wholely or partly remain available for production of biomass. The specific growth rate is expressed here as a function of the intracellular “concentration” of the limiting substrate, defined as the amount of substrate within the cells per unit of cell dry weight. In the model, the intracellular substrate is divided into two parts. One part is a “structural” substrate not available for further growth. The other part is an “excess” or “functional” substrate that is used for biomass production and is assumed to be converted into structural substrate proportionally to growth. The rate of growth is believed to be controlled by the intracellular concentration of excess substrate.     

Application of a noninhibitory growth model to predict the transient response in a chemostat

A method of adapting a kinetic model based on steady-state chemostat data to predict the transient performance of a chemostat culture is presented. The proposal provides for a time delay which can be considered equivalent to a period of reduced activity of the organism subsequent to the introduction of a step change in operating conditions. The adapted kinetic model gives substantially better performance in predicting the transient response of an experimental system than the unmodified kinetic model.     

A predictive model for combined temperature and water activity on microbial growth during the growth phase

An empirical and generalized model is presented, based on a modified Arrhenius equation, for predicting the combined effect of temperature and water activity on the growth rate of bacteria. When it was applied to seven separate sets of wide ranging published results, spanning some 50 years and including a spore-former and a silage micro-organism, predictions explained between 92.9 and 99.0% of the variation in the results with an overall mean of 96.6%. Advantages over existing models are that it is relatively easy to fit to data using least squares regression and requires only five coefficients. These, together with its simplicity and demonstrated wide application, will facilitate its practical use.     

A predictive model for combined temperature and water activity on microbial growth during the growth phase

An empirical and generalized model is presented, based on a modified Arrhenius equation, for predicting the combined effect of temperature and water activity on the growth rate of bacteria. When it was applied to seven separate sets of wide ranging published results, spanning some 50 years and including a spore-former and a silage micro-organism, predictions explained between 92.9 and 99.0% of the variation in the results with an overall mean of 96.6%. Advantages over existing models are that it is relatively easy to fit to data using least squares regression and requires only five coefficients. These, together with its simplicity and demonstrated wide application, will facilitate its practical use.     

A novel membrane bioreactor for microbial growth

A novel membrane bioreactor, previously assessed for its gas transfer characteristics, was used in various size and membrane configurations for the growth of the strictly aerobic bacterium Pseudomonas aeruginosa. The bioreactor was found to readily support growth, and the initial growth rates showed the previously demonstrated enhanced effect in gas O₂ mass transfer of the dimpled membrane bioreactor over flat membrane bioreactors. The production of a secondary metabolite by a Pseudomonas sp. following growth was demonstrated, as was the biotransformation of a nitrile by Nocardia rhodochrous with the removal of the biotransformation products across a membrane. The potential of the bioreactor, in terms of other applications in the field of biotechnology, is disscussed. Correspondence to: A. M. Nicholson     

Hypothetical model for monitoring microbial growth by using capacitance measurements--a minireview.

Microbiological impedance devices are used routinely by food and manufacturing industries, and public health agencies to measure microbial growth and metabolism. In this paper a hypothetical model explaining the effects of microbial growth and metabolism on capacitance at electrode-medium interfaces, that can be supported by fundamental theories and principles of electrochemistry, is presented. This model provides a framework to interpret changes in capacitance during microbial growth and metabolism and can be used to generate and test hypotheses on factors (i.e., temperature, microbial cell density, microbial growth and medium conductivity) contributing to increases or decreases in capacitance.     

A discrete, size-structured model of microbial growth and competition in the chemostat

A nonlinear matrix model of a size-structured microbial population growing on a scarce nutrient in a chemostat, derived by Gage et al. [6], is modified to include two competing populations. It is shown that competitive exclusion results. The winner is the population able to grow at the lower nutrient concentration.Research partially supported by NSF Grant DMS 9300974     

A model of microbial growth in a plug flow reactor with wall attachment

A mathematical model of microbial growth for limiting nutrient in a plug flow reactor which accounts for the colonization of the reactor wall surface by the microbes is formulated and studied analytically and numerically. It can be viewed as a model of the large intestine or of the fouling of a commercial bio-reactor or pipe flow. Two steady state regimes are identified, namely, the complete washout of the microbes from the reactor and the successful colonization of both the wall and bulk fluid by the microbes. Only one steady state is stable for any particular set of parameter values. Sharp and explicit conditions are given for the stability of each, and for the long term persistence of the bacteria in the reactor.     

A mechanism of microbial cell growth

Presently empirical expressions, especially the Monod equation, are used to quantitatively relate microbial growth rate to limiting substrate concentration in the solution. In this paper microbial growth is postulated to occur by a mechanism involving a mass transfer or assimilation process. The assimilation process is assumed to be substrate mass transfer limited and hence proportional to the limiting substrate concentration. The ingestion is assumed independent of limiting substrate concentration and only dependent upon internal reaction rates. The quantitative relationship between limiting substrate and microbial growth rate resulting from this mechanism is developed. Under certain limiting conditions this expression is shown to reduce to the Monod equation and under other conditions it reduces to the Lotka-Volterra relationship. This mechanism is applied to batch and continuous cultures and the results obtained are compared quantitatively with experiment.     

A thermodynamic theory of microbial growth

Our ability to model the growth of microbes only relies on empirical laws, fundamentally restricting our understanding and predictive capacity in many environmental systems. In particular, the link between energy balances and growth dynamics is still not understood. Here we demonstrate a microbial growth equation relying on an explicit theoretical ground sustained by Boltzmann statistics, thus establishing a relationship between microbial growth rate and available energy. The validity of our equation was then questioned by analyzing the microbial isotopic fractionation phenomenon, which can be viewed as a kinetic consequence of the differences in energy contents of isotopic isomers used for growth. We illustrate how the associated theoretical predictions are actually consistent with recent experimental evidences. Our work links microbial population dynamics to the thermodynamic driving forces of the ecosystem, which opens the door to many biotechnological and ecological developments.     

A microprocessor-controlled photometer for monitoring microbial growth in multi-welled plates

Multi-welled microtitre plates provide a convenient means of handling 'large block' multifactorial experiments with microbial cultures. An inexpensive instrument, termed a 'Biophotometer', has been designed to monitor microbial growth in each well, by transmitted light measurements. Optional microcomputer control is employed to facilitate scanning of plates and data handling. A unique method for agitating cultures is incorporated into the system. Typical results are presented to illustrate the versatility of this system.     

A microprocessor-controlled photometer for monitoring microbial growth in multi-welled plates

Multi-welled microtitre plates provide a convenient means of handling 'large block' multifactorial experiments with microbial cultures. An inexpensive instrument, termed a 'Biophotometer', has been designed to monitor microbial growth in each well, by transmitted light measurements. Optional microcomputer control is employed to facilitate scanning of plates and data handling. A unique method for agitating cultures is incorporated into the system. Typical results are presented to illustrate the versatility of this system.