Environmental Engineering Reference
In-Depth Information
chemical reactions, and consequently they have been extensively studied. They can
catalyze numerous reactions and result in both decomposition and intermediate
compounds being present. Extracellular enzymes, which decompose proteins, fats,
hydrocarbons, and cellulose, should be expected to occur in any soil that has these
components in it. Some common examples of enzymes found in soil and their source are
given in Table 9.6.
Enzymes are often associated with the mineral fraction in soil. The association of
enzymes with clay minerals in particular has been extensively investigated. Often such
associations are more active catalytically than are the enzymes alone, thus even when the
enzymes do not occur freely in the soil solution they may still be present and active [24].
Some inorganic and even some organic components in soil may catalyze the same
reactions as enzymes, however. Peroxide decomposition and hydrolysis can be promoted
by inorganic ions, exchange sites, and organic molecules at normal soil temperatures
[24], thus the observation of a reaction occurring in soil may not always be clearly related
to enzymes alone.
Other compounds may also be exuded into the environment by organisms. Some may
be simple organic waste products and others complex molecules that the organism cannot
use. These may include intermediate decomposition products from the breakdown of
pesticides and insecticides.
Microbial, plant, and animal cells in or added to the soil both exude material and break
open, releasing their contents. Any intercellular component may thus be found in soil at
any time. Many of these compounds are easily decomposed by other organisms and so do
not last long in the soil environment. Some compounds may become associated with clay
particles and become a little more resistant to further decay. In the decomposition process
many intermediates are found and may be part of a mix of compounds found in a soil
analysis.
Cellular components that are not easily decomposed will also be present. These may
include both organic compounds and inorganic compounds. Microorganisms can reduce
sulfate, nitrate, selenium, and
TABLE 9.6 Some Common Extracellular Enzymes and Their Common Source
Enzyme
Source
Proteases, cellulases, and pectic and
proteolytic enzymes
Numerous bacteria and fungi
Cellulase
Fungi
Lipases
Fungi and other microorganisms
Phosphatase
Bacillus, Fusarium, Saccharomyces, and many other
soil bacteria and fungi
Source: Taken from Ref. 24.
other elements to their elemental form, and these may thus be present in soil from this
 
Search WWH ::




Custom Search