Rates of Microbial Growth

The poor correlation between bacterial growth rate and droplet size is due partly to the limitations of the light microscope method used (Dolby, 1965). Other influencing factors are nutrient level, salt and pH of the droplet 

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Density indicator strips are used to monitor the rate of microbial growth. These strips are attached to the culture vessel. As the microbes multiply, the solution becomes cloudy, obscuring some of the shaded strips. The degree of visibility of the shaded strips indicates the density of the microbes. In this activity, you will observe the bioremediation effectiveness of the fungus Penicillium and the bacteria Pseudomonas on a sample of oil. 

A typical bacterial growth according to the Monod prediction is depicted in Figure 13.6. As the concentration of substrate increases, the rate of microbial growth... 

Water activity has a profound effect on the rate of many chemical reactions in foods and on the rate of microbial growth (Labuza 1980). This information is summarized in Table 1-9. Enzyme activity is virtually nonexistent in the monolayer water (aw between 0 and 0.2). Not surprisingly, growth of microorganisms at this level of aw is also virtually zero. Molds and yeasts start to grow at aw between 0.7 and 0.8, the upper limit of capillary water. Bacterial growth takes place when aw reaches 0.8, the limit of loosely... 

Figure 11. Rate of microbial growth during combined Alcalase and microbial dehalogenation treatment ofPAE resin.

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. 

The relationship of microbial growth and chemical removal (Eqs. 17-64 and 17-65) implies that when the chemical is present at low levels ([z] K,M), its instantaneous rate of degradation (i.e., at a particular time t, and microbial abundance, [B],) is linearly proportional to its concentration and the concentration of the microorganisms reacting with it ... 

Concentration. A major characteristic of microbial growth and enzymatic conversion processes is low concentrations. The rates of these processes are inhibited by even moderate concentrations of most low molecular weight organic substances, even 1 g/L often being harmful. Nutrients also must be limited, for instance, the following in g/L ... 

Two possible explanations can be readily put forward as to why this form of equation should be suitable for describing the dependence of microbial growth rate on feed concentration. The first of these is that the equation has the same form as the theoretically based Michaelis-Menten equation used to describe enzyme kinetics. The chemical reactions occurring inside a microbial cell are generally mediated by enzymes, and it would be reasonable to suppose that one of these reactions is for some reason slower than the others. As a result the growth kinetics of the micro-organism would be expected to reflect the kinetics of this enzyme reaction, probably modified in some way, but in essence having the form of the Michaelis-Menten equation. 

Contois, D. E. J. Gen. Microbiol. 21 (1959) 40. Kinetics of microbial growth. Relationship between population density and specific growth rate of continuous culture. 

Understanding the growth kinetics of microbial, animal, or plant cells is important for the design and operation of fermentation systems employing them. Cell kinetics deals with the rate of cell growth and how it is affected by various chemical and physical conditions. 

The microbial reaction is given by S —> P. This is catalyzed by X, which also grows. The rate of production growth rx of the microorganism X is given by... 

Price PB, Sowers T (2004) Temperature dependence of metabolic rates for microbial growth, maintenance, and survival. Proc Natl Acad Sci 101 4631-4636... 

The strict separation of microbial growth and biotransformation offers some advantages. Thus, each step can be optimized individually, and a negative influence of the substrate or its product excluded. Furthermore, the hydroxylation rate in water-suspended mycelia sometimes... 

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