Microbial Remediation of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 136

(Sharma et al. 2010). Dichlorodiphenyltrichloroethane (DDT) is still persisting in some
parts of the developing countries. An isolate of Sphingobacterium sp. is observed to uti-
lize DDT, dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethyl-
ene (DDE) in soil. Based on the metabolite's detection, a pathway is proposed for DDT
degradation by the isolated strain in which it undergoes dechlorination, hydrogenation,
dioxygenation, decarboxylation, hydroxylation, and phenyl-ring cleavage reactions to
complete the mineralization process (Fang et al. 2010). A Pseudomonas strain isolated from
tea rhizosphere demonstrated capacity for the degradation of miticide propargite (Sarkar
et al. 2010). Klebsiella jilinsis strain 2N3, which is isolated from industrial wastewater treat-
ment pond, degraded chlorimuron-ethyl, sulfonylurea herbicides ethametsulfuron, met-
sulfuron-methyl, nicosulfuron, rimsulfuron, and tribenuron-methyl (Zhang et al. 2010).
Immobilization of Burkholderia cepacia strain PCL3 on corncob increased the percentage of
carbofuran removal (96.97%) (Plangklang and Reungsang 2010). Azotobacter chroococcum
strain JL 102 exhibited lindane degradation at 10 ppm concentration on the 8th week of
incubation (Anupama and Paul 2010). A bacillus strain B3 ( Paenibacillus polymyxa ) isolated
from peanut rhizosphere is observed to be capable of utilizing beta-cypermethrin, chlor-
pyrifos, and imidacloprid as the sole source of carbon for growth. The isolate showed
bioremediation capabilities and a broad inhibition spectrum against various soil-borne
phytopathogenic fungi as well (An and Zhao 2009). A soil bacterium Providencia stuartii
strain MS09 utilized chlorpyrifos as the sole carbon source at 50-700 mg/L (Rani et al.
2008). Klebsiella sp. strain 1805, isolated from the soil of soybean field, is found capable
of degrading Opera (a fungicide containing epoxiconazole and pyraclostrobin) (Lopes
et al. 2010). Evidence shows that bacteria on leaves also can degrade organophosphate
pesticides and demonstrated that phyllosphere bacteria have great potential for the biore-
mediation of pesticides in situ, where the environment is hostile to nonepiphytic bacteria.
Bacterial species from the genera Sphingomonas , Acidovorax , and Chryseobacterium were
found to degrade dichlorvos, an organophosphorus pesticide sprayed on rape phyllo-
sphere (Ning et al. 2010).
5.3.1 Genetically Engineered Bacteria
With the advent of latest molecular techniques, genetically engineered strains have
been showing promise for in situ remediation of organophosphate-contaminated sites
with broader substrate specificity in combination with the rapid degradation rate.
A native soil bacterium, Stenotrophomonas sp. (strain YC-1), that produces methyl para-
thion hydrolase (MPH) was genetically engineered with the ice nucleation protein from
Pseudomonas syringae . The genetically engineered bacterial strain was able to degrade a
mixture of six organophosphate pesticides (0.2 mM each) completely within 5 h (Yang
et al. 2010).
5.3.2 Culture-Independent Study
A complete picture of the microbial community structure and their subsequent persis-
tence for the remediation of a pesticide-contaminated site can only be measured through
culture-independent study of the metagenome. However, experimental reports based
on culture-independent techniques are scarce. Paul et al. (2006) conducted a culture-
independent study to remediate p-nitrophenol (PNP)-contaminated soil site using the
efficient PNP-degrading organism Arthrobacter protophormiae RKJ100. PNP is a metab-
olite arising from the conversion of the organophosphorus pesticides, parathion and