Microbial kinetics

For those pesticides which are utilized as microbial growth substrates, sigmoidal rates of biodegradation are frequentiy observed (see Fig. 2). Sigmoidal data are more difficult to summarize than exponential (first-order) data because of their inherent nonlinearity. Sigmoidal rates of pesticide metabohsm can be described using microbial growth kinetics (Monod) however, four kinetics constants are required. Consequentiy, it is more difficult to predict the persistence of these pesticides in the environment. 

It is necessary to estabUsh a criterion for microbial death when considering a sterilization process. With respect to the individual cell, the irreversible cessation of all vital functions such as growth, reproduction, and in the case of vimses, inabiUty to attach and infect, is a most suitable criterion. On a practical level, it is necessary to estabUsh test criteria that permit a conclusion without having to observe individual microbial cells. The failure to reproduce in a suitable medium after incubation at optimum conditions for some acceptable time period is traditionally accepted as satisfactory proof of microbial death and, consequentiy, stetihty. The appHcation of such a testing method is, for practical purposes, however, not considered possible. The cultured article caimot be retrieved for subsequent use and the size of many items totally precludes practical culturing techniques. In order to design acceptable test procedures, the kinetics and thermodynamics of the sterilization process must be understood. 

Monod kinetics Kinetics of microbial cell growth as a function of substrate concentration proposed by Jacques Monod and widely used to understand growth-substrate relationships. 

Several of the problems associated with whole cell bioprocesses are related to the highly effective metabolic control of microbial cells. Because cells are so well regulated, substrate or product inhibition often limits the concentration of desired product that can be achieved. This problem is often difficult to solve because of a poor understanding of the kinetic characteristics of the metabolic pathway leading to the desired product. 

Non-stirred, aerated vessels are used in the process for traditional products such as wine, beer and cheese production. Most of the newly found bioprocesses require microbial growth in an aerated and agitated system. The percentage distribution of aerated and stirred vessels for bioreactor applications is shown in Table 6.1. The performances of various bioreactor systems are compared in Table 6.2. Since these processes are kinetically controlled, transport phenomena are of minor importance. 

The cells activities have been described based on a multi-species biofilm model, and the microbial kinetics by a mathematical model. Using this model predicts that the biomass on the external surface of the biofilm has higher activity than the biomass near the solid support surface, and that condition may occur, after the biofilm has reached a critical dept or formed... 

A Langmuir-Hanes plot based on the Monod rate equation is presented in Figure 8.7. The Monod kinetic model can be used for microbial cell biocatalyst and is described as follows ... 

Methyl-l,10-undecadiene, ADMET polymerization of, 442 Michaelis-Menten enzymatic kinetics, 84 Microbial hydrolysis, 43 Microcellular elastomers, 204-205 Microphase-separated block copolymers, 6-7... 

Application of an aldolase to the synthesis of the tricyclic microbial elicitor (-)-syringolide (Figure 10.34) is another excellent example that enzyme-catalyzed aldolizations can be used to generate sufficient quantities of enantiopure material in multistep syntheses of complex natural and unnatural products [159]. Remarkably, the aldolase reaction established absolute and relative configuration of the only chiral centers that needed to be externally induced in the adduct (95) from achiral precursor (94) during the subsequent cyclization events, all others seemed to follow by kinetic preference. 

Microbial kinetics can be quite complex. Multiple steady states are always possible, and oscillatory behavior is common, particularly when there are two or more microbial species in competition. The term chemostat can be quite misleading for a system that oscillates in the absence of a control system. 

Hwang H-M, RE Hodson, DL Lewis (1989) Microbial degradation kinetics of toxic organic chemicals over a wide range of concentrations in natural aquatic systems. Environ Toxicol Chem 8 65-74. 

Klecka GM, WJ Maier (1988) Kinetics of microbial growth on mixtures of pentachlorophenol and chlorinated aromatic compounds. Biotechnol Bioeng 31 328-335. 

Paris DF, JE Rogers (1986) Kinetic concepts for measuring microbial rate constants effects of nutrients on rate constants. Appl Environ Microbiol 51 221-225. 

The application of substrates isotopically labeled in specific positions makes it possible to follow the fate of individual atoms during the microbial degradation of xenobiotics. Under optimal conditions, both the kinetics of the degradation, and the formation of metabolites may be followed— ideally when samples of the labeled metabolites are available. Many of the classical studies on the microbial metabolism of carbohydrates, carboxylic acids, and amino acids used radioactive... 

Tas DO, IN Thomson, FE Loffler, SG Pavlostathis (2006) Kinetics of the microbial reductive dechlorination of pentachloroaniline. Environ Sci Technol 40 4467-4472. 

Rossetti S, LL Blackall, M Majone, P Hugenholtz, JJ Plumb, V Tandoi (2003) Kinetic and phylogenetic characterization of an anaerobic dechlorinating microbial community. Microbiology (UK) 149 459-469. 

Microbial Biotransformation. Microbial population growth and substrate utilization can be described via Monod s (35) analogy with Michaelis-Menten enzyme kinetics (36). The growth of a microbial population in an unlimiting environment is described by dN/dt = u N, where u is called the "specific growth rate and N is microbial biomass or population size. The Monod equation modifies this by recognizing that consumption of resources in a finite environment must at some point curtail the rate of increase (dN/dt) of the population ... 

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