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Fumio Matsumura
therefore, is not to give an encyclopedic coverage of the subject areas, but rather
to give the basic concept of the general mechanisms of pesticidal degradation
in the environment. Examples are usually cited to clarify the point of interest.
Also, the contributions of plants and animals in the overall metabolic changes
of pesticide residues in the environment are not considered, since they are covered
by other contributors. However, some nonenzymatic reactions which often contribute to the overall degradation of pesticides in the environment are described.
3.2. CHARACTERISTICS OF MICROBIAL METABOLISM
It was originally assumed by many pesticide scientists that the patterns of
microbial metabolism were in general very similar to the ones already found in
animals, particularly the mammalian species, since studies on microbial metabolism of pesticides were lagging far behind the comparable studies in mammalian
species. However, as knowledge on microbial degradation has advanced, it has
become apparent that in many cases the patterns of degradation in these two
different groups of organisms are often very different.
First of all, the purpose of all metabolic reactions on xenobiotics in higher
animals is to eventually convert them into polar and therefore excretable forms.
Second, in higher animals the processes of primary metabolism of xenobiotics
are centralized in a few specialized organs. In the case of the liver, its metabolic
pattern is largely determined by the activity of an oxidative detoxification system,
generally termed mixed-function oxidase.
On the contrary, the predominant metabolic activities in the microbial world
are meant for production of energy. In this respect, it is not even possible to
define xenobiotics here, since most organic materials can serve as the source of
energy to at least some microorganisms. Here only a few groups of chemicals
may be regarded as foreign to microorganisms. Among insecticidal compounds,
the halogen-containing chemicals, particularly halogenated aromatics, must be
regarded as foreign (or unusable) material to microorganisms.
Another characteristic or microbial metabolism is the adaptability of microorganisms to changing environments through mutation and induction, particularly toward chemicals that are initially toxic to them. The case of penicillin
resistance in bacteria through induction of penicillinase is well known.
The metabolic activities of microorganisms encompass many different types
of biological processes not found in any other organisms. They include fermentation, some types of anaerobic metabolism, chemolithotrophic metabolism, and
metabolism through exoenzymes.
In general, microbial contributions to metabolic alteration of insecticides
may be classified in several categories as shown in Table 3.1.
Fumio Matsumura
therefore, is not to give an encyclopedic coverage of the subject areas, but rather
to give the basic concept of the general mechanisms of pesticidal degradation
in the environment. Examples are usually cited to clarify the point of interest.
Also, the contributions of plants and animals in the overall metabolic changes
of pesticide residues in the environment are not considered, since they are covered
by other contributors. However, some nonenzymatic reactions which often contribute to the overall degradation of pesticides in the environment are described.
3.2. CHARACTERISTICS OF MICROBIAL METABOLISM
It was originally assumed by many pesticide scientists that the patterns of
microbial metabolism were in general very similar to the ones already found in
animals, particularly the mammalian species, since studies on microbial metabolism of pesticides were lagging far behind the comparable studies in mammalian
species. However, as knowledge on microbial degradation has advanced, it has
become apparent that in many cases the patterns of degradation in these two
different groups of organisms are often very different.
First of all, the purpose of all metabolic reactions on xenobiotics in higher
animals is to eventually convert them into polar and therefore excretable forms.
Second, in higher animals the processes of primary metabolism of xenobiotics
are centralized in a few specialized organs. In the case of the liver, its metabolic
pattern is largely determined by the activity of an oxidative detoxification system,
generally termed mixed-function oxidase.
On the contrary, the predominant metabolic activities in the microbial world
are meant for production of energy. In this respect, it is not even possible to
define xenobiotics here, since most organic materials can serve as the source of
energy to at least some microorganisms. Here only a few groups of chemicals
may be regarded as foreign to microorganisms. Among insecticidal compounds,
the halogen-containing chemicals, particularly halogenated aromatics, must be
regarded as foreign (or unusable) material to microorganisms.
Another characteristic or microbial metabolism is the adaptability of microorganisms to changing environments through mutation and induction, particularly toward chemicals that are initially toxic to them. The case of penicillin
resistance in bacteria through induction of penicillinase is well known.
The metabolic activities of microorganisms encompass many different types
of biological processes not found in any other organisms. They include fermentation, some types of anaerobic metabolism, chemolithotrophic metabolism, and
metabolism through exoenzymes.
In general, microbial contributions to metabolic alteration of insecticides
may be classified in several categories as shown in Table 3.1.