70
Fumio Matsumura
are degraded by either broad-spectrum enzymes such as hydrolases, reductases,
and oxidases or by specific enzymes commonly present in high percentages of
microorganisms. In either case the pesticidal substrates are metabolized as a
result of general microbial activities. In the environment, therefore, those types
of reactions are observed in which microbial activities are stimulated by the
availability of nutrients and moisture, and by the right temperature and pH.
3.2. 1.2. Analog-Induced Metabolism
The term cometabolism has been used in the past to include all a, b, and
c types of metabolism. However, in this chapter I have decided to apply the
term in a more restricted manner to include only the cases where the microorganisms are induced by chemicals which structurally resemble the pesticide
molecules. Thus, to avoid confusion, I shall use the term analog-induced metabolism here. In such a case the microorganisms can grow on the given chemical
(analog) but not on the pesticide, despite their capability to at least partially
metabolize the latter. Good examples are those produced by Focht and Alexander
(1970a-c), who obtained DDT-degrading Hydrogenomonas sp. (Pseudomonas
sp.) by using diphenylmethane as a carbon source, and those produced by Ahmed
and Focht (1972) and Furukawa and Matsumura (1975), who selected PCBmetabolizing microorganisms by using biphenyl as a carbon source. The important feature distinguishing this type from other incidental metabolisms is that
these microorganisms are purposely selected by nonpesticidal analogs. The enzyme systems induced do not initially recognize the difference in the substrate
molecules and therefore partially degrade the pesticide molecules. However, in
such cases the microorganisms are incapable of completing the metabolism necessary to receive energy for growth.
3.2. 1.3. Catabolism
In catabolism microorganisms are capable of deriving energy from the
pesticide molecules and therefore can grow on them. I include here cases in
which only a part of the pesticide molecule is utilized for growth from a practical
standpoint. Thus a complete mineralization of the pesticide is not the absolute
requirement so long as growth is observed by using the pesticide as a sole carbon
source.
3.2.2. Criteria for Distinguishing One Type of Metabolism
from Another
It is also important to realize that in the case of types a and b metabolism
microorganisms depend for their survival upon other more accessible carbon
Fumio Matsumura
are degraded by either broad-spectrum enzymes such as hydrolases, reductases,
and oxidases or by specific enzymes commonly present in high percentages of
microorganisms. In either case the pesticidal substrates are metabolized as a
result of general microbial activities. In the environment, therefore, those types
of reactions are observed in which microbial activities are stimulated by the
availability of nutrients and moisture, and by the right temperature and pH.
3.2. 1.2. Analog-Induced Metabolism
The term cometabolism has been used in the past to include all a, b, and
c types of metabolism. However, in this chapter I have decided to apply the
term in a more restricted manner to include only the cases where the microorganisms are induced by chemicals which structurally resemble the pesticide
molecules. Thus, to avoid confusion, I shall use the term analog-induced metabolism here. In such a case the microorganisms can grow on the given chemical
(analog) but not on the pesticide, despite their capability to at least partially
metabolize the latter. Good examples are those produced by Focht and Alexander
(1970a-c), who obtained DDT-degrading Hydrogenomonas sp. (Pseudomonas
sp.) by using diphenylmethane as a carbon source, and those produced by Ahmed
and Focht (1972) and Furukawa and Matsumura (1975), who selected PCBmetabolizing microorganisms by using biphenyl as a carbon source. The important feature distinguishing this type from other incidental metabolisms is that
these microorganisms are purposely selected by nonpesticidal analogs. The enzyme systems induced do not initially recognize the difference in the substrate
molecules and therefore partially degrade the pesticide molecules. However, in
such cases the microorganisms are incapable of completing the metabolism necessary to receive energy for growth.
3.2. 1.3. Catabolism
In catabolism microorganisms are capable of deriving energy from the
pesticide molecules and therefore can grow on them. I include here cases in
which only a part of the pesticide molecule is utilized for growth from a practical
standpoint. Thus a complete mineralization of the pesticide is not the absolute
requirement so long as growth is observed by using the pesticide as a sole carbon
source.
3.2.2. Criteria for Distinguishing One Type of Metabolism
from Another
It is also important to realize that in the case of types a and b metabolism
microorganisms depend for their survival upon other more accessible carbon