Microbial Remediation of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 137

methyl parathion. The bacterial community structure was profiled using terminal
restriction fragment length polymorphism (T-RFLP) so that any changes during imple-
mentation of the bioremediation could be assessed. Microbial community composition
was also determined by 16S rRNA gene clone library, followed by sequencing of the
individual clones. Sequencing of representative clones of each phylotype showed that
the community structure of the pesticide-contaminated soil was mainly constituted by
the members of the Proteobacteria and Actinomycetes. The 16S rRNA gene pool ampli-
fied from the soil metagenome and T-RFLP studies revealed 46 different phylotypes on
the basis of similar banding patterns. The study demonstrated that bioaugmentation
of contaminated soil with A. protophormiae stimulated complete degradation of PNP
under field conditions. The study also demonstrated that none of the treatments (strain
inoculation and/or addition of corncob powder) significantly influenced the parameters,
species richness and evenness of the community composition, in the soils. In another
culture-independent study, the dominant benzene degraders (responsible for 13C
uptake) were determined by comparing relative abundance of T-RFLP phylotypes in
heavy fractions of labeled benzene (13C) amended samples to the controls (from unla-
beled benzene amended samples). Two phylotypes ( Polaromonas sp. and Acidobacterium
sp.) were the major benzene degraders in the microcosms constructed from the soil of
the contaminated site; whereas one phylotype (“candidate” phylum TM7; unclassified
Sphingomonadaceae) incorporated the majority of the benzene-derived 13C in each of
the agricultural soils (Xie et al. 2010).
5.3.3 Microbial Consortia
Microbial remediation is a complex biological system including synergism and antag-
onism. For example, pyrene degradation in the rhizosphere commonly involves the
activity of bacterial consortia in which various species of bacteria interact to achieve
PAH degradation (Balcom and Crowley 2010). Methanogenic granular sludge and
wastewater fermented sludge were used as inocula for batch tests of anaerobic biore-
mediation of chlorinated-pesticide-contaminated soil. Results showed that 80%-90%
of γ-hexachlorocyclohexane (γ-HCH), 1,1,1-trichloro-2,2-bis-(4-methoxyphenyl)ethane
(methoxychlor), and DDT were removed in 4-6 weeks. Residual fractions of these pes-
ticides persisted till the end of the 16-week experiment. DDT was degraded through
DDD (Baczynskia and Pleissner 2010). Microbial consortium present in the cow-dung
slurry was used for the remediation of fenvalerate (a synthetic pyrethroid) amended soil
(Geetha and Fulekar 2010).
5.4 Archaea
Little information exists about the ability of archaea to degrade pesticides. Recently,
alkane-degrading halophilic archaeal strains were isolated. One (strain MSNC 2) was
closely related to Haloarcula sp. and three (strains MSNC 4, MSNC 14, and MSNC 16) were
closely related to Haloferax sp. Biodegradation assays showed that depending on the strain,
32%-95% (0.5 g/l) of heptadecane was degraded after 30 days of incubation at 40°C in
225 g/l NaCl artificial medium. One of the strains of Haloarcula (MSNC 14) was also able to
degrade phenanthrene (Tapilatu et al. 2010).