Microbial Remediation of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 139

A polypore fungus, Ganoderma australe , was found to have the potential to degrade lin-
dane. The optimum lindane biodegradation (3.11 mg biodegradation of lindane per gram
of biomass) was observed in liquid-agitated sterile cultures with a nitrogen content of
1.28 g/L, lindane concentration of 7.0 ppm, temperature of 18.0°C, and cultivation time of
5 days (Dritsa et al. 2009).
Organophosphorus pesticides are widely used for protection of agricultural yields.
However, these pesticides pose various threats to organisms, including humans, and
hamper soil microbial activity. Aspergillus oryzae strain ARIFCC 1054 was found to pos-
sess phosphatase activity and capable of degrading organophosphorus pesticides such as
monocrotophos (Bhalerao and Puranik 2009). Wood-rotting fungi were also used for the
degradation of a wide spectrum of recalcitrant organopollutants. Transformation of diel-
drin to 9-hydroxydieldrin was found by a wood-rotting fungus, Phlebia brevispora strain
YK543. The P. brevispora strain YK543 degraded 39.1 ± 8.8% of dieldrin during 30 days of
incubation (Kamei et al. 2010).
5.5.1 Hybridization
Studies have demonstrated the ability to genetically augment the metabolic capabilities of
naturally occurring fungi. Genetically engineered strains were capable of ex situ environ-
mental remediation of a variety of widely used neurotoxic organophosphate pesticides. A
hybrid genetic system formed by the combination of a bacterial structural gene in a fungal
expression system has been developed and productively introduced into the common soil
fungus, Gliocladium virens . The hybrid gene was formed by combining the constitutive
promoter and translational signals from a fungal gpd gene (encoding glyceraldehyde-3-
phosphate-dehydrogenase) with the structural region of the bacterial opd gene (organo-
phosphate-degrading gene). Organophosphate hydrolase (OPH, encoded by the opd gene)
activity was detected in several of the genetic transformants, and the levels of expres-
sion were greatly enhanced (>20 fold) as compared to transformants with nonhomolo-
gous fungal genetic sequences (Xu et al. 1996). Because of its structure, atrazine is not
easily degraded. Its partial degradation is possible by fungus, but its total mineralization
is not possible by a single microorganism (Levanon 1993). In fact, it is necessary to have
two or more different kinds of microorganisms capable of the degradation of atrazine
(Radosevich et al. 1995) to achieve total mineralization, although some reports point out
that, in some cases, even the presence of various microorganisms is not enough to attain
this (Korpraditskul et al. 1993).
5.6 Cyanobacteria
Cyanobacteria are photoautotrophic, and some can fix atmospheric nitrogen. Therefore,
their use for bioremediation of surface waters would circumvent the need to supply bio-
degradative heterotrophs with organic nutrients (Kuritz and Wolk 1995). Cyanobacteria
can derive energy from sunlight and carbon from the air. Some cyanobacteria are also able
to fix atmospheric nitrogen (van-Baalen 1987) and are therefore especially inexpensive to
maintain. Filamentous cyanobacteria, including nitrogen-fixing strains that combine aero-
bic metabolism in their vegetative cells with anaerobic metabolism in their differentiated
cells called heterocysts (Wolk et al. 2004), are widespread in many ecosystems, including