Microorganism growth rate

Typical response times are of the order 15-30 minutes (i), days (ii), and several days (iii). The net microorganism growth rate is a key design parameter and its reciprocal is termed sludge age or mean cell residence time. An adequate control has to take into consideration, that the growth rate is time-varying (5). 

TABLE 7-13 Relationship of Maximum Microorganism Growth Rate Under Various, Practically Defined Redox Conditions... 

It is well known that ATP is a major physiological parameter in cells, so that firefly luciferase is used for BL detection of bacterial contaminations, activity estimations of erythrocytes after blood conservation and antibiotic effects. BL measurements of microorganism growth rates is applied to assess antibiotic substrates, where the level of inhibition is most important. Information about the appropriate antibiotic treatment of open infections is received within 2-3 hours [28]. 

Mechanism of Action. The mechanisms by which antibiotic adrninistration at subtherapeutic levels enhance growth rate and efficiency of gain in growing animals have not been clarified. Possible modes of action include disease control, nutrient sparing, and metaboHc effects. There is extensive evidence that the principal benefit from subtherapeutic use of antibiotics results from the control of harmfiil microorganisms. 

Sobecky PA, MA Schell, MA Moran, RE Hodson (1992) Adaptation of model genetically engineered microorganisms to lake water growth rate enhancements and plasmid loss. Appl Environ Microbiol 58 3630-3637. 

The importance of including soil-based parameters in rhizosphere simulations has been emphasized (56). Scott et al. u.sed a time-dependent exudation boundary condition and a layer model to predict how introduced bacteria would colonize the root environment from a seed-based inoculum. They explicitly included pore size distribution and matric potential as determinants of microbial growth rate and diffusion potential. Their simulations showed that the total number of bacteria in the rhizosphere and their vertical colonization were sensitive to the matric potential of the soil. Soil structure and pore size distribution was also predicted to be a key determinant of the competitive success of a genetically modified microorganism introduced into soil (57). The Scott (56) model also demonstrated that the diffusive movement of root exudates was an important factor in determining microbial abundance. Results from models that ignore the spatial nature of the rhizosphere and treat exudate concentration as a spatially averaged parameter (14) should therefore be treated with some caution. 

Table I. Comparison of soil samples with regard to total number of microorganisms isolated and the percentage of total causing severe toxicity (growth rating < 2 or germination < 75% of controls) to cucumber (Cucu), barnyard grass (Bygr), and cress...

When microorganisms use an organic compound as a sole carbon source, their specific growth rate is a function of chemical concentration and can be described by the Monod kinetic equation. This equation includes a number of empirical constants that depend on the characteristics of the microbes, pH, temperature, and nutrients.54 Depending on the relationship between substrate concentration and rate of bacterial growth, the Monod equation can be reduced to forms in which the rate of degradation is zero order with substrate concentration and first order with cell concentration, or second order with concentration and cell concentration.144... 

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