Metabolic quotients

In practice, carbon limited chemostat cultures are used to estimate the P/O quotient These conditions are used because they favour the most efficient conversion of the carbon substrate into cellular material, ie the highest efficiency of energy conservation. The steady state respiration rate (qo,) is measured as a function of dilution rate (specific growth rate) and Yq can be obtained from the reciprocal of the slope of the plot. qo, is also known as the metabolic quotient for oxygen or the specific rate of oxygen consumption. 

Fig. 1. Effects of long-term land use on organic C, extractable C, microbial biomass C, microbial quotient, basal respiration and the metabolic quotient of soils (0-10 cm). Bars are S.E. (From Haynes, unpublished, 2005). 

From the measurements of microbial biomass C and basal respiration the metabolic quotient (qC02) can be calculated. This is a measure of microbial... 

It has been suggested (Insam and Haselwandter 1989 Anderson and Domsch 1990) that the metabolic quotient can be used as an index of ecosystem development. As an ecosystem reaches maturity, selection pressure towards efficient use of available resources results in a larger microbial biomass with a lower metabolic quotient. Nonetheless, Wardle and Ghani (1995) concluded that qC02 can be insensitive to disturbance and ecosystem development, fails to distinguish between effects of disturbance and stress and does not decline predictably in response to ecosystem development wherever stress increases along successional gradients. 

Certainly, calculation of the metabolic quotient can reveal trends very different from those of basal respiration. As shown in Fig. 1, for the 7 land uses, trends in basal respiration were broadly similar to those for microbial biomass C and organic C. However, when the metabolic quotient was calculated, trends with land use were very different. Values were greater under sugarcane, maize and to a lesser extent annual ryegrass, than the other treatments. This suggests that the microbial community under these arable land uses is under more stress and/or has a different composition to that under the others. The most likely microbial stress under these land uses is likely to be a shortage of available substrate C. 

Metabolic quotient Variable often in the range of 2-40pg C02-C mg-1 biomass day-1 Basal respiration per unit of microbial biomass C. Provides a useful measure of the efficiency with which microbes are using substrate C. Often used as an index of the degree of microbial stress. 

Anderson TH, Domsch KH (1993) The metabolic quotient for C02 (qC02) as a specific activity parameter to assess the effects of environmental conditions, such as pH, on the microbial biomass of the soil. Soil Biol Biochem 25 393-395... 

Wagai R, Sollins P (2002) Biodegradation and regeneration of water-soluble carbon in a forest soil leaching column study. Biol Fertil Soils 35 18-26 Wardle DA, Ghani A (1995) A critique of the microbial metabolic quotient (qC02) as a bioindicator of disturbance and ecosystem development. Soil Biol Biochem 27 1601-1610... 

The best way to characterize cell metabolic patterns is in terms of consumption rates and production rates per viable cell (collectively termed metabolic quotients). This allows much easier comparison between different cell types or culture conditions than do plots of changes in the levels of nutrients or products over time. It also shows directly how metabolic patterns change with time during batch growth... 

Note that will be negative for nutrients that are consumed by the cells and positive for products. In order to obtain positive values for all of the metabolic quotients, it is customary to speak in terms of the specific substrate (nutrient) consumption rate and the specific product formation rate p ... 

For semi-batch systems the metabolic quotients are as in Equation 4.2.33 ... 

Metabolic quotients are easily determined in continuous culture. At steady state, the derivative terms in Equation 4.2.31 may be set equal to zero, thereby allowing... 

Figure 42.7 Metabolic quotients for the glucose step change experiment described in Figure 4.2.5. (a) Specific glucose consumption rate (mmol glucose consumed viable celL da>r ) as a function of culture time, (b) Specific lactate production rate (mmol lactate produced viable celH day" ) as a function of culture time. Adapted from Miller et al (1989) by permission of Biotechnology and Bioengineering.

Estimation of cell density using metabolic quotients... 

Actinomycetes Microbial biomass Metabolic quotient Substrate-induced respiration Microbial biomass Soil organic carbon Dehydrogenase activity... 

The metabolic quotient, or specific respiration rate (qCO-, is the ratio of the basal respiration rate (as CO2-C) per unit MBC, and provides an indication of efficiency of microbial in utilization of available substrates (Anderson and Domsch, 1993). Low C02 in detritus of the impacted site suggests poor efficiency of microbes in utilization of available substrates (DeBusk and Reddy, 1998 Wright and Reddy, 2001b). Minimal differences in qC02 were observed for 0-10 cm soil of impacted and reference sites. Consumption of electron acceptors such as oxygen, nitrate, and sulfate during... 

Qojj Qaoewtej tC. metabolic quotients expressed in /il-metabolite/mg. dry weight/hr. 

Metabolic quotients expressed in microliters me-tabolite/mg dry weight/hour Increment of free energy Standard free energy change Standard free energy change at pH 7... 

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