Microbial kinetics importance

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. 

Applying the foregoing thermodynamic and kinetic information to manganese behavior in natural water systems is considerably limited because the manganese system exemplifies the difficulties discussed earlier. On the thermodynamic side, the kinds of oxide phases in natural waters may not correspond to those for which equilibrium data are available. Also, cation exchange reactions are probably important (21). On the kinetic side, the role of catalysis by various mineral surfaces in suspension or in sediments is not really known. Of considerable importance may be microbial catalysis of the oxidation or reduction processes, as described by Ehrlich (7). With respect to the real systems, relatively... 

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. 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

Kinetic experiments with synthetic iron oxyhydroxides have shown that the initial microbial reduction rate increases with increasing initial ferric iron concentration up to a given maximum reduction rate (Bonneville et al. 2004). This observation was explained by a saturation of active membrane sites with Fe(III) centers. The respective reaction was best described with a Michaelis-Menten rate expression with the maximum reduction rate per cell positively correlating with the solubility of the iron oxyhydroxides (Bonneville et al. 2004). Kinetic studies involving iron are not only inherently important to describe reaction pathways and to derive rate constants, which can be used in models. Kinetic studies also increasingly focus on iron isotopic fractionation to better understand the iron isotopic composition of ancient sediments, which may assist in the reconstruction of paleo-environments. Importantly, iron isotope fractionation occurs in abiotic and biotic processes the degree of isotopic fractionation depends on individual reaction rates and the environmental conditions, e.g. whether reactions take place within an open or closed system (Johnson et al. 2004). 

Dissolved arsenic concentrations can be limited either by the solubility of minerals containing arsenic as a constituent element (or in solid solution) or by sorption of arsenic onto various mineral phases. For both the precipitation-dissolution of arsenic-containing minerals and sorption-desorption of arsenic onto solid phases, equilibrium calculations can indicate the level of control over dissolved arsenic concentrations that can be exerted by these processes. However, neither of these types of reactions is necessarily at equilibrium in natural waters. The kinetics of these reactions can be very sensitive to a variety of environmental parameters and to the level of microbial activity. In particular, a pronounced effect of the prevailing redox conditions is expected because potentially important sorbents (e.g., Fe(III) oxyhydroxides) are unstable under reducing conditions and because of the differing solubilities of As(V) and As(III) solids. 

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