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Fumio Matsumura
dition of extra nutrient to increase microbial growth, and yet other circumstances
exist where the addition of the same nutrient can shut off the degradation activities. Generally speaking, the more specific the metabolic route and the more
difficult in developing the metabolizing microbes, the less likely it is that the
addition of nutrients would help degradation activities.
The cases of resistance development would be more prevalent with fungicides: the phenomena could well lead to the failure of crop protection or any
other intended result.
Nonenzymatic Processes. The processes by which microbial activities contribute to the overall alteration of insecticidal molecules by nonenzymatic mechanisms are less well studied than those involving enzymatic reactions. It is known
that some pesticidal chemicals can be photochemically altered in the environment, and microbial products can promote photochemical reactions in two ways.
First, microbial products can act as photosensitizers by absorbing the energy
from light and transmitting it to the insecticidal molecule. We have been able
to show, for instance, that an aqueous extract from heat-sterilized blue-green
algal cultures promoted photochemical degradation of DDT (Esaac and Matsumura, 1979). Another way that microbial products can facilitate such photochemical reactions is to serve as donors or acceptors of electrons and/or reacting
groups of chemicals, for example, hydrogen and OH-, which are often needed
for photochemical reactions.
Recently Esaac and Matsumura (1980) demonstrated that ferridoxin and
fiavoproteins isolated from algae are powerful photosensitizers. These are known
to play important roles in electron transfer systems in algae. Since they are quite
stable molecules, it would not be suprising if they persist long enough in the
environment after the death and lysing of algae cells to become a factor in
pesticide degradation.
The effect of pH is often neglected in the field of pesticide metabolism
despite numerous reports on the pH-dependent reactions of relatively labile molecules, both in soil and in vitro. Large pH changes are often associated with
microbial activities together with changes in nutritional sources, particularly in
aqueous media. Initially degradation of proteins causes alkaline pHs, and with
carbohydrate metabolism the pH becomes acid. While the actual occurrence of
microbial pH effects in nature might be difficult to document, it is certainly easy
to demonstrate the phenomenon in vitro, where during the decay period the pH
of spent culture media often becomes very low. Incubation of labile insecticides
such as tetraethyl pyrophosphate (TEPP) with such spent medium under sterile
conditions would certainly cause breakdown of the insecticides.
Little attention has been paid so far to the importance of the microbial
formation of organic products capable of reacting with pesticides. Such reactants
of microbial origin can be postulated to include amino acids, peptides, alkylating
Fumio Matsumura
dition of extra nutrient to increase microbial growth, and yet other circumstances
exist where the addition of the same nutrient can shut off the degradation activities. Generally speaking, the more specific the metabolic route and the more
difficult in developing the metabolizing microbes, the less likely it is that the
addition of nutrients would help degradation activities.
The cases of resistance development would be more prevalent with fungicides: the phenomena could well lead to the failure of crop protection or any
other intended result.
Nonenzymatic Processes. The processes by which microbial activities contribute to the overall alteration of insecticidal molecules by nonenzymatic mechanisms are less well studied than those involving enzymatic reactions. It is known
that some pesticidal chemicals can be photochemically altered in the environment, and microbial products can promote photochemical reactions in two ways.
First, microbial products can act as photosensitizers by absorbing the energy
from light and transmitting it to the insecticidal molecule. We have been able
to show, for instance, that an aqueous extract from heat-sterilized blue-green
algal cultures promoted photochemical degradation of DDT (Esaac and Matsumura, 1979). Another way that microbial products can facilitate such photochemical reactions is to serve as donors or acceptors of electrons and/or reacting
groups of chemicals, for example, hydrogen and OH-, which are often needed
for photochemical reactions.
Recently Esaac and Matsumura (1980) demonstrated that ferridoxin and
fiavoproteins isolated from algae are powerful photosensitizers. These are known
to play important roles in electron transfer systems in algae. Since they are quite
stable molecules, it would not be suprising if they persist long enough in the
environment after the death and lysing of algae cells to become a factor in
pesticide degradation.
The effect of pH is often neglected in the field of pesticide metabolism
despite numerous reports on the pH-dependent reactions of relatively labile molecules, both in soil and in vitro. Large pH changes are often associated with
microbial activities together with changes in nutritional sources, particularly in
aqueous media. Initially degradation of proteins causes alkaline pHs, and with
carbohydrate metabolism the pH becomes acid. While the actual occurrence of
microbial pH effects in nature might be difficult to document, it is certainly easy
to demonstrate the phenomenon in vitro, where during the decay period the pH
of spent culture media often becomes very low. Incubation of labile insecticides
such as tetraethyl pyrophosphate (TEPP) with such spent medium under sterile
conditions would certainly cause breakdown of the insecticides.
Little attention has been paid so far to the importance of the microbial
formation of organic products capable of reacting with pesticides. Such reactants
of microbial origin can be postulated to include amino acids, peptides, alkylating