Microbial biomass, measuring, substrate

Historically, measurement of the microbial biomass has been a tedious, time-consuming occupation involving staining and direct counting or use of culture media and enumeration of individual microbial communities. However, in the last 20 years, a suite of methods have been developed for more rapid assessment of the microbial biomass. These include the substrate-induced respiration method (Anderson and Domsch 1978), the chloroform fumigation-incubation method (Jenkinson and... 

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. 

Although the investigations of both Raunkjaer et al. (1995) and Almeida (1999) showed that removal of COD — measured as a dissolved fraction — took place in aerobic sewers, a total COD removal was more difficult to identify. From a process point of view, it is clear that total COD is a parameter with fundamental limitations, because it does not reflect the transformation of dissolved organic fractions of substrates into particulate biomass. The dissolved organic fractions (i.e., VFAs and part of the carbohydrates and proteins) are, from an analytical point of view and under aerobic conditions, considered to be useful indicators of microbial activity and substrate removal in a sewer. The kinetics of the removal or transformations of these components can, however, not clearly be expressed. Removal of dissolved carbohydrates can be empirically described in terms of 1 -order kinetics, but a conceptual formulation of a theory of the microbial activity in a sewer in this way is not possible. The conclusion is that theoretical limitations and methodological problems are major obstacles for characterization of microbial processes in sewers based on bulk parameters like COD, even when these parameters are determined as specific chemical or physical fractions. 

Following excess glucose addition to soil, there is a rapid increase in the rate of evolution of C02-C. Over the first 2 hours, the increase in C02-C is proportional to the size of the initial microbial biomass. After this time the relationship weakens as new microbial cells proliferate (Anderson and Domsch 1978). This method, usually termed substrate induced respiration, provides a rapid means of measuring the microbial biomass. Lin and Brookes (1999a) also showed that it was strongly correlated with ATP and biomass C measured by microscopy. The SIR method, in combination with the use of an antibiotic (streptomycin) and a fungicide (cyclohexamide) can also provide... 

As one component of the decade-long VERTEX program, an oceanic time-series station (33°N, 139°W) was occupied for an 18-month period from October 1986 to May 1988. During this observation period, the site was visited on 7 occasions ( 90-day interval) for approximately 1 week per expedition to retrieve and redeploy a free-drifting sediment trap array, to collect water samples and to conduct experiments relevant to C- and N-cycle processes (Harrison et al., 1992 Knauer et al., 1990). The uptake and assimilation of NOa and NH4 substrates were measured during incubation experiments that were designed to assess, and correct for, isotope dilution of the added tracers. Photoautotrophic N assimilation was measured using the into protein method, described later in this section. Measurements were also made of the concentrations of NOs , NH4, DON, PON, total microbial biomass, autotrophic biomass, heterotrophic biomass, primary productivity and the export of particulate matter (Harrison et al, 1992). In many ways this was, at that time, the most comprehensive study of the marine N-cycle ever conducted in the North Pacific trades biome. 

Biomass is a fundamental parameter in the characterization of microbial growth. Direct measurement of biomass is not possible in SSF because microbial biomass cannot be separated from the substrate. But absolute amount of biomass is important for the calculation of growth rates and yields. Since direct measurement of biomass is difficult, a global stoichiometric equation of microbial growth can be considered. 

Knight BP, McGrath SP, Chaudri AM (1997) Biomass carbon measurements and substrate utilization patterns of microbial populations from soils amended with cadmium, copper, or zinc. Appl Environ Microbiol 63 39 43... 

The OUR is an activity-related quantitative measure of the aerobic biomass influence on the relationship between the electron donor (organic substrate) and the electron acceptor (dissolved oxygen, DO). It is a measure of the flow of electrons through the entire process system under aerobic conditions (Figure 2.2). The OUR versus time relationship of wastewater samples from sewers becomes a backbone for analysis of the microbial system. This relationship is crucial for characterization of the suspended wastewater phase in terms of COD components and corresponding kinetic and stoichiometric parameters of in-sewer processes. 

Without appropriate cleanup measures, BTEX often persist in subsurface environments, endangering groundwater resources and public health. Bioremediation, in conjunction with free product recovery, is one of the most cost-effective approaches to clean up BTEX-contaminated sites [326]. However, while all BTEX compounds are biodegradable, there are several factors that can limit the success of BTEX bioremediation, such as pollutant concentration, active biomass concentration, temperature, pH, presence of other substrates or toxicants, availability of nutrients and electron acceptors, mass transfer limitations, and microbial adaptation. These factors have been recognized in various attempts to optimize clean-up operations. Yet, limited attention has been given to the exploitation of favorable substrate interactions to enhance in situ BTEX biodegradation. 

Heat flux calorimeters are bioreactors equipped with special temperature control tools. They provide a sensitivity which is approximately two orders of magnitude better than that of microcalorimeters, e.g. [33,258]. The evaluation and description of microbial heat release is based on a heat balance heat yields and the heat of combustion of biological components are central parameters for quantification [70]. Measurements obtained so far have been used to investigate growth, biomass yield, maintenance energy, the role of the reduction degree of substrates, oxygen uptake [414] and product formation [272]. 

State, types of functional groups), redox potential, pH, nutrient and carbon availability, contaminant bioavailability and concentration, electron acceptors, temperature, salinity, and microbial consortia and biomass (D Angelo, 2002). Reaction rates can vary over several orders of magnitude depending on these environmental factors. Studies have documented the effects of several of these factors on rates of mineralization of contaminants in wetland substrates. Redox potential, a measure of the electron availability and an indirect measure of the oxygen status, has been used to show certain compounds degrade favorably under aerobic conditions (e.g., naphthalene), others under anaerobic conditions (e.g., DDT), and still others under moderately anaerobic conditions (e.g., polychlorobi-phenyls [PCBs]). 

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