be degraded either slowly via successive N-dealkylations
and accumulation of stable metabolites or much more
rapidly via dechlorination and breaking of the side chains
to form cyanuric acid which is then further mineralized. Soil
pH regulates the balance between these two metabolic
pathways (Houot et al. 2000). In some cases the enzymatic
machinery can be operated via microbial consortia, each
member carrying out a few metabolic steps forward. For a
number of chemicals, we could expect the preexistence of a
potential for degradation distributed in different microbial
hosts, immediately efficient, or after structural changes of
recruited enzymes. It has long been realized that the intrinsic
biodegradation of a xenobiotic compound was better
evaluated in environments showing high specific microbial
richness such as soils or sewage sludge. More than an
increased metabolic efficiency of microbial communities
compared to pure strains, it is now established that they
also represent a framework where different microrganisms
harboring gene exchange may contribute to the emergence
of new gene combinations making possible emergence of
novel biochemical capacities. The possibility that extrachromosomal elements can cause dispersion in the soil microflora of characters they code for was suggested as soon as the
early 1970s (Waid 1972). “Horizontal gene transfer” involves
all the mechanisms of transformation, conjugation, and transduction. The evolutionary advantages of gene transfer may be
extended inside the cell by different mechanisms of transposition that affect gene order and may contribute to the emergence of new operons. The dispersion of a newly acquired
metabolic “competence” in a degrading metapopulation has
been regarded as a process of stabilization (Bull 1980). Some
have even seen in such a dispersion process the opportunity
for genes to survive according to the evolutionary theory of
“selfish gene” (Reanney 1976).
16.7.3 Pesticides
Since its settlement and development of agriculture and
livestock, man had to protect his products and crops against
various pests and diseases. To control them, he naturally
turned to chemical substances of natural origin of which he
had previously recognized the biocidal character. Thus,
since antiquity, civilizations around the Mediterranean Sea
have used as insecticides extracts of pyrethrum flower heads
or tobacco leaves. From the fifth century, the Chinese used
preparations of arsenic for the same purpose. The Egyptians
used petroleum oil to control the growth of phytopathogenic
fungi. In 1878 the “Bordeaux mixture,” a solution of copper
sulfate supplemented with lime, was prepared by the
chemist Ulysse Gayon (1845–1929). With the botanist
Alexis Millardet (1838–1902), they developed a means of
protecting vineyards against mildew. It has been widely used
to fight against diseases related to fungal attack.
Many synthetic pesticides appear early in the twentieth
century. This is the case, for example, of dinitro-ortho-cresol
(DNOC), which was synthesized in the late 1920s and
patented in France by Truffaut and Pastac in 1932 for
weeding grain. In 1935, the pesticide phenothiazine was
commercialized by DuPont factory. In 1938, the Swiss
chemist Paul Mu ¨ller (1899–1965) discovered the insecticidal properties of DDT further marketed in 1946. In 1948,
he received the Nobel Prize in Physiology and Medicine.
DDT has been widely used by the Allies during the Second
World War. The discovery just after the Second World War
of the first selective herbicides, the hormone herbicides,
contributed to extensive development of chemical control.
In 1944, Mitchell and Hamner of the USDA mentioned the
possibility of using synthetic growth regulators, including
2,4-D, as selective herbicides. Since that time and during the
last 60 years, industrial countries have developed farming
practices largely based on an extensive use of pesticides
that have contributed to improving the quality and yield
of crops with increasingly detrimental consequences for
the environment. With rare exceptions, surface and deepwater reserves contain residues of pesticides that pose a
potential danger to human health. Fortunately, these residues
mainly pass through the soil with the purifying action of
abundant and active microorganisms that help to reduce their
concentration. Advances in knowledge of the physiological
and biochemical aspects of microbial degradation of
pesticides are needed both to define environmental friendly
molecules and to develop strategies for remediation of
contaminated sites.
16.7.3.1 Pesticides in the Environment:
A Few Figures
The sale and use of synthetic organic molecules that help
fight against pests was regulated by a European Directive
(Directive 91/414/EC), which has established a procedure
for assessing the risk to the consumer, the user, and
the environment. This Directive was recently repealed by
the regulation (EC) N
1107/2009 adopted with the new
Directive 2009/128/EC “establishing a framework for Community action to achieve the sustainable use of pesticides.”
The need to register all of the molecules within the new EU
law has contributed to a significant reduction of authorized
pesticides. For instance, in 2013, a total of 1,297 active
substances were listed in the EU Pesticide database. Only
428 are approved in Europe and 317 in France, the largest
market of pesticides in Europe (http://e-phy.agriculture.
gouv.fr/). Since 1999, the use of pesticides has decreased
from 89,100 tons of synthetic products to 48.800 tons in
2011 (www.uipp.org/). However, this trend should be
taken with caution. Indeed, the ban on old molecules applied
at high doses and the placing on the market of new active
products applied at very low doses have probably
16 Applied Microbial Ecology and Bioremediation
685
and accumulation of stable metabolites or much more
rapidly via dechlorination and breaking of the side chains
to form cyanuric acid which is then further mineralized. Soil
pH regulates the balance between these two metabolic
pathways (Houot et al. 2000). In some cases the enzymatic
machinery can be operated via microbial consortia, each
member carrying out a few metabolic steps forward. For a
number of chemicals, we could expect the preexistence of a
potential for degradation distributed in different microbial
hosts, immediately efficient, or after structural changes of
recruited enzymes. It has long been realized that the intrinsic
biodegradation of a xenobiotic compound was better
evaluated in environments showing high specific microbial
richness such as soils or sewage sludge. More than an
increased metabolic efficiency of microbial communities
compared to pure strains, it is now established that they
also represent a framework where different microrganisms
harboring gene exchange may contribute to the emergence
of new gene combinations making possible emergence of
novel biochemical capacities. The possibility that extrachromosomal elements can cause dispersion in the soil microflora of characters they code for was suggested as soon as the
early 1970s (Waid 1972). “Horizontal gene transfer” involves
all the mechanisms of transformation, conjugation, and transduction. The evolutionary advantages of gene transfer may be
extended inside the cell by different mechanisms of transposition that affect gene order and may contribute to the emergence of new operons. The dispersion of a newly acquired
metabolic “competence” in a degrading metapopulation has
been regarded as a process of stabilization (Bull 1980). Some
have even seen in such a dispersion process the opportunity
for genes to survive according to the evolutionary theory of
“selfish gene” (Reanney 1976).
16.7.3 Pesticides
Since its settlement and development of agriculture and
livestock, man had to protect his products and crops against
various pests and diseases. To control them, he naturally
turned to chemical substances of natural origin of which he
had previously recognized the biocidal character. Thus,
since antiquity, civilizations around the Mediterranean Sea
have used as insecticides extracts of pyrethrum flower heads
or tobacco leaves. From the fifth century, the Chinese used
preparations of arsenic for the same purpose. The Egyptians
used petroleum oil to control the growth of phytopathogenic
fungi. In 1878 the “Bordeaux mixture,” a solution of copper
sulfate supplemented with lime, was prepared by the
chemist Ulysse Gayon (1845–1929). With the botanist
Alexis Millardet (1838–1902), they developed a means of
protecting vineyards against mildew. It has been widely used
to fight against diseases related to fungal attack.
Many synthetic pesticides appear early in the twentieth
century. This is the case, for example, of dinitro-ortho-cresol
(DNOC), which was synthesized in the late 1920s and
patented in France by Truffaut and Pastac in 1932 for
weeding grain. In 1935, the pesticide phenothiazine was
commercialized by DuPont factory. In 1938, the Swiss
chemist Paul Mu ¨ller (1899–1965) discovered the insecticidal properties of DDT further marketed in 1946. In 1948,
he received the Nobel Prize in Physiology and Medicine.
DDT has been widely used by the Allies during the Second
World War. The discovery just after the Second World War
of the first selective herbicides, the hormone herbicides,
contributed to extensive development of chemical control.
In 1944, Mitchell and Hamner of the USDA mentioned the
possibility of using synthetic growth regulators, including
2,4-D, as selective herbicides. Since that time and during the
last 60 years, industrial countries have developed farming
practices largely based on an extensive use of pesticides
that have contributed to improving the quality and yield
of crops with increasingly detrimental consequences for
the environment. With rare exceptions, surface and deepwater reserves contain residues of pesticides that pose a
potential danger to human health. Fortunately, these residues
mainly pass through the soil with the purifying action of
abundant and active microorganisms that help to reduce their
concentration. Advances in knowledge of the physiological
and biochemical aspects of microbial degradation of
pesticides are needed both to define environmental friendly
molecules and to develop strategies for remediation of
contaminated sites.
16.7.3.1 Pesticides in the Environment:
A Few Figures
The sale and use of synthetic organic molecules that help
fight against pests was regulated by a European Directive
(Directive 91/414/EC), which has established a procedure
for assessing the risk to the consumer, the user, and
the environment. This Directive was recently repealed by
the regulation (EC) N
1107/2009 adopted with the new
Directive 2009/128/EC “establishing a framework for Community action to achieve the sustainable use of pesticides.”
The need to register all of the molecules within the new EU
law has contributed to a significant reduction of authorized
pesticides. For instance, in 2013, a total of 1,297 active
substances were listed in the EU Pesticide database. Only
428 are approved in Europe and 317 in France, the largest
market of pesticides in Europe (http://e-phy.agriculture.
gouv.fr/). Since 1999, the use of pesticides has decreased
from 89,100 tons of synthetic products to 48.800 tons in
2011 (www.uipp.org/). However, this trend should be
taken with caution. Indeed, the ban on old molecules applied
at high doses and the placing on the market of new active
products applied at very low doses have probably
16 Applied Microbial Ecology and Bioremediation
685