Nutrients Organic compounds

Soil type and structure also influence the dynamics of rhizosphere microbial populations. Whether nutrients are available for bacteria in the rhizosphere often depends on the sites in the soil where nutrients are present. Organic compounds tightly bound to the soil matrix are often less available for bacteria (226), and those present in smaller pore spaces can be physically protected against mineralization. However, disturbance of the soil often cau.ses these nutrients to become more available to soil microbes (227). 

Figure 1 Diagrammatic representation of the nondimensional profiles of mineral nutrients and organic compounds in the. soil surrounding a root. Note that the width of the rhizosphere (arbitrary units) differs for different solutes.

The primary metabolism of an organic compound uses a substrate as a source of carbon and energy. For the microorganism, this substrate serves as an electron donor, which results in the growth of the microbial cell. The application of co-metabolism for bioremediation of a xenobiotic is necessary because the compound cannot serve as a source of carbon and energy due to the nature of the molecular structure, which does not induce the required catabolic enzymes. Co-metabolism has been defined as the metabolism of a compound that does not serve as a source of carbon and energy or as an essential nutrient, and can be achieved only in the presence of a primary (enzyme-inducing) substrate. 

Conversion of an organic compound to another organic compound without the microorganism using the compound as a nutrient. Resulting compounds may be as toxic (DDT to DDE or DDD) or less toxic (xylenes to toluic acid). 

When microorganisms use an organic compound as a sole carbon source, their specific growth rate is a function of chemical concentration and can be described by the Monod kinetic equation. This equation includes a number of empirical constants that depend on the characteristics of the microbes, pH, temperature, and nutrients.54 Depending on the relationship between substrate concentration and rate of bacterial growth, the Monod equation can be reduced to forms in which the rate of degradation is zero order with substrate concentration and first order with cell concentration, or second order with concentration and cell concentration.144... 

The subject of this chapter will be the most important mechanisms by which microorganisms mobilise substrates. We will thereby focus on the mobilisation of nonliving food molecules, and will not deal with living food organisms. Besides organic compounds, we will also treat the biological mechanisms to acquire iron as the least bioavailable inorganic nutrient in many environments. 

There is only one simple anion commonly found in soil, and that is chloride (Cl ). Chloride is an essential nutrient for plants but is typically present in sufficiently high concentrations that deficiencies are never observed. If other halogens are present, they will also be present as simple anions. Most soils do contain small amounts of bromide as the second most common simple anion. In some cases, significant levels of fluoride and iodide may be present, although this is rare. These anions are generally soluble in water and tend to exist as the simple anion. However, they can combine with other components and exist as other species. For instance, halogens are present in organic compounds such as solvents, insecticides, and herbicides, which can be soil contaminants. There are also other nonionic species of these elements that may be present [20],... 

The experimental determination of COD for most organic compounds agrees well with the theoretically predicted value (TOD) but the BOD is almost always lower. This is to be expected, because complete oxidation does not take place in the aquatic environment. The COD BOD ratio can therefore be regarded as a measure of aquatic biodegradability. The closer this value is to 1 the greater the aquatic biodegradability of the compound. In industrial nutrient discharges it is usually the case that the effluent contains a mixture of nutrients of uncertain composition. It is therefore not possible to... 

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