Microbes Model

We take two cases in which mineral surfaces catalyze oxidation or reduction, and one in which a consortium of microbes, modeled as if it were a simple enzyme, promotes a redox reaction. In Chapter 33, we treat the question of modeling the interaction of microbial populations with geochemical systems in a more general way. 

The typical bioreactor is a two-phase stirred tank. It is a three-phase stirred tank if the cells are counted as a separate phase, but they are usually lumped with the aqueous phase that contains the microbes, dissolved nutrients, and soluble products. The gas phase supplies oxygen and removes by-product CO2. The most common operating mode is batch with respect to biomass, batch or fed-batch with respect to nutrients, and fed-batch with respect to oxygen. Reactor aeration is discussed in Chapter 11. This present section concentrates on reaction models for the liquid phase. 

Therefore if the carbon substrate is present at sufficiently high concentration anywhere in the rhizosphere (i.e., p p, ax), the microbial biomass will increase exponentially. Most models have considered the microbes to be immobile and so Eq. (33) can be solved independently for each position in the rhizosphere provided the substrate concentration is known. This, in turn, is simulated by treating substrate-carbon as the diffusing solute in Eq. (32). The substrate consumption by microorganisms is considered as a sink term in the diffusion equation, Eq. (8). 

Miki T, Ushio M, Fukui S, Kondoh M. Functional diversity of microbial decomposers facilitates plant coexistence in a plant-microbe-soil feedback model. Proceedings of the National Academy of Sciences of the United States of America, 2010.107 pp. 14251-14256. doi 10.1073/pnas.0914281107. 

Nazaries L, Murrell JC, Millard P, Baggs L, Singh BK. Methane, microbes and models Fundamental understanding of the soil methane cycle for future predictions. Environ. Microbiol. 2013 15 2395-2417. 

K. Heincke, B. Demuth, H. J. Joerdening, and K. Buchholz, Kinetics of the dextransucrase acceptor reaction with maltose Experimental results and modeling, Enzyme Microb. Technol., 24 (1999) 523-534. 

It is in principle possible for a free enzyme to promote reaction in a geochemical system, but enzyme kinetics are invoked in geochemical modeling most commonly to describe the effect of microbial metabolism. Microbes are sometimes described from a geochemical perspective as self-replicating enzymes. This is of course a considerable simplification of reality, as we will discuss in the following chapter (Chapter 18), since even the simplest metabolic pathway involves a series of enzymes. 

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Microbiologists have developed ways to model microbial growth and, using assumptions related to the expected behavior of organisms under different environmental conditions, these models are then coupled with dose-response models with the result that risks (responses) can be estimated, given a certain degree of knowledge about initial microbe counts and the environmental conditions (related... 

Figure 4.15 indicates the range of rates of O2 consumption in different soils. Oxygen is consumed in oxidation of inorganic reductants, such as Fe(II), as well as in oxidation of organic matter by microbes. Bouldin (1968) and Howeler and Bouldin (1971) compared measured rates of O2 movement into anaerobic soil cores with the predictions of various models, and obtained the best fits with a model allowing for both microbial respiration and abiotic oxidation of mobile and immobile reductants abiotic oxidation accounted for about half the O2 consumed. The kinetics of the abiotic reactions are complicated. They often depend on the adsorption of the reductant on solid surfaces as, for example, in... 

Next, we tried model degradation by using esterase from microbes. As shown in Fig. 12, the major products under this condition were butylmonosuccinate and butyldisuccinate. This shows that the degradation in early stage is carried out by extracellular enzymes like esterase. 

The first weakness was that the Chemical Co-evolution Model was least convincing when applied to the most diverse, most ancient NP producers—the microbes. As explained above, many microbiologists simply did not find the model convincing when applied to microbes because very little real evidence for the model came from studies of microbes. The main evidence arising from studies of microbes was that some... 

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