Maintenance coefficient

The interesting features are (1) X goes to zero and S reaches as D approaches [1 (2) S is not a function of when D is less than (3) the maintenance coefficient is very important at low dilution rate but has httle effect afterwards and (4) is never so high that [L can be reached, thus washout always occurs before [L and is a function of S. ... 

Maintenance energy requirements can be defined in terms of rate of substrate consumption per unit of biomass for maintenance this is known as the maintenance coefficient (m). 

Use the data to determine the maintenance coefficient (m) and the maximum growth yield Y. ... 

Here, Ms is the maintenance coefficient for substrate S. Typical units of Ms are grams of substrate per gram of dry cell mass per hour. Table 12.1 gives maintenance coefficients for various organisms and substrates. The maintenance... 

TABLE 12.1 Maintenance Coefficients for Various Organisms and Substrates... 

Turning to the substrate balance, yeast cells contain about 50% carbon. The cell mass is measured as total dry weight, not just carbon. This gives Yx/s = 2 when S is measured as the carbon equivalent of glucose. A reasonable value for Yxis is 1 so that half the carbon goes into biomass and half meets the associated energy requirements. The maintenance coefficient in carbon-equivalent units is 0.008 h . Using these parameter estimates, the three simultaneous ODEs for 5" > 0, become... 

Ms Maintenance coefficient, mass of substrate per dry cell mass per time 12.15... 

Barber and Lynch (9) used this equation to recalculate data from previous studies on microbial growth in soil, using a constant maintenance coefficient (///). They found no case where energy input exceeded the requirement for maintenance, and suggested, therefore, that apart from zones immediately around recently incorporated plant and animal residues, appreciable and continuous activity in soils can be expected only in the rhizosphere. 

The constant kd is referred to as the endogenous respiration coefficient or the specific maintenance rate. Pirt(45) points out that kd is proportional to m, the maintenance coefficient defined in equation 5.51 ... 

A limitation of the methods described so far is that they have assumed a constant overall yield coefficient and do not allow the endogenous respiration coefficient kd (or alternatively the maintenance coefficient, m) to be evaluated. Equation 5.54 shows that the overall yield, as measured when monitoring a batch reactor, is affected by the growth rate and has the greatest impact when the growth rate is low. Consequently, it is desirable to be able to estimate the values of kd or m, so that the yield coefficient reflects the true growth yield. An equivalent method would be one where the specific rates of formation of biomass and consumption of substrate were determined independently, again without the assumption of a constant overall yield-coefficient. 

Abbott, B. J. and Clamen, A. Biotechnoi. Bioeng. 15 (1973) 117. The relationship of substrate, growth rate, and maintenance coefficient to single cell protein production. 

The maintenance coefficient can explain the non-growth associated substrate consumption for energy production, an energy that supports transmembrane ions gradient, motility, among other functions. 

For Equations 62 and 63, the maintenance coefficient appears limited by substrate through a Monod-type formulation. 

Figure 2. Theoretical estimates of C required to meet maintenance energy demands (solid circles) by different sized microbial populations calculated using a maintenance coefficient of 0.0126 /tg C//tg biomass-C/hr derived from Anderson and Domsch (18). Cumulative C requirements are compared to the cumulative C supplied during first-order decomposition of a pesticide having a 20-day half-life applied at 1 /tg C/g soil. Limited growth would be possible when carbon supply exceeded the maintenance requirement.

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