Abstract:
Unsustainable agricultural practices and excessive usage of pesticides have
provoked severe pollution problems worldwide as well as in Pakistan. As the population
in the world is increasing, so is the need for more production which directly implies more
application of fertilizers and pesticides in the field. Only 0.1% of the pesticide reaches to
the target whereas the remaining ends up in the environment. Extensive usage of
pesticides ultimately finds their way into soil, water and air thus polluting them.
Chlorpyrifos (CPF) belongs to a class of pesticides called organophosphates and about
38% of the pesticides all over the world are organophosphates. Chlorpyrifos serves as a
potential contaminant in aquatic and terrestrial ecosystem and it is also harmful to
humans. Biodegradation offers the most viable option for CPF degradation by employing
indigenous microorganisms. It has been reported that in pesticide contaminated soils,
indigenous microorganisms such as bacteria develop a mechanism to withstand high
concentrations of pesticides/chemicals by using the pesticide as their carbon and energy
source hence biodegrading the pesticide, these bacteria are called pesticide tolerant
bacteria. The present study was performed as an attempt to isolate and identify CPF
tolerant bacterial strains from the soils sprayed and contaminated with CPF keeping in
consideration the biodegradation aspect. The objective of the study was to isolate,
characterize and identify CPF tolerant bacterial strains which may possess the potential
for biodegradation of CPF. The study was conducted by using different
concentrations(conc.) of CPF i.e., 1000pppm, 3000ppm, 5000ppm, 10000ppm,
15000ppm and 20000ppm. The bacterial strains which tolerated the lower concentrations
were isolated and grown on higher concentrations. The strains were then isolated,
purified and examined morphologically and Polymerase chain reaction (PCR) and 16S
rRNA was performed to identify them. Out of the 43 isolated bacterial population, 20
bacterial strains could withstand higher concentrations of CPF i.e., 15000ppm and
20000ppm and they were sent for 16s rRNA gene sequencing. Seven different genera
were identified from the isolated bacterial population named Planococcus,
staphylococcus, Kytococcus, Micrococcus, Bacillus, Escherichia and Ochrobactrum. In
these studies, a candidate novel species was also identified based upon phylogenetic3
analysis. It is concluded that a diverse group of bacterial population exist in CPF
contaminated soil.
