MSc

The present study on “Isolation, characterization and evaluation of soil microorganisms for bioremediation of chlorpyrifos”, was conducted in the Department of Agricultural Microbiology at College of Agriculture, Vellayani during 2012-14, with the objective of isolation, characterization and evaluation of microorganisms for chlorpyrifos degradation, development of consortia and evaluation of bioremediation potential against chlorpyrifos in vivo. Microorganisms capable of degradation of chlorpyrifos were isolated by enrichment culture technique from identified locations with high residue levels of chlorpyrifos. In all, nineteen isolates comprising eleven bacteria, seven fungi and one actinomycete obtained were subjected to a preliminary screening based on the ability of isolates to utilize 50,100,200,400 and 800 ppm concentrations of chlorpyrifos at intervals of 7, 15, 20, 25, 30 DAI. The six isolates selected (M5, M6, M7, M10, M12, M17) were further evaluated for their ability to degrade different concentrations of chlorpyrifos based on population build up , analysis of chlorpyrifos residue and chloride released into the medium. The fungal isolates, M5, M6, M7 and M17 which recorded significant growth in terms of viable count, maximum reduction in chlorpyrifos residue and release of chloride were selected and subjected to morphological and molecular characterization. The isolates M5, M6, M7 and M17 were identified as Isaria farinosa, Aspergillus fumigatus, Trichoderma viride and Penicillium griseofulvum respectively.

In order to develop a consortium, the compatibility of the selected fungal isolates - M5, M6, M7 and M17 was tested by co-culturing in liquid MSM and by dual culture technique. All the fungal isolates were compatible and no inhibition could be recorded. A consortium of the four fungal isolates was prepared in liquid formulation and its ability to degrade different concentrations of chlorpyrifos was studied under in vitro conditions on 25th day of inoculation. The percentage degradation of chlorpyrifos by the isolates increased with increase in concentrations, but showed a decline at 800 ppm. The percentage degradation of chlorpyrifos was higher in consortium compared to individual isolates under in vitro conditions.

The developed liquid consortium was evaluated in sterilized soil spiked with 100 and 400 ppm concentration of chlorpyrifos with cowpea as the test crop. Significant reduction in all biometric characters was observed due to spiking with chlorpyrifos at 100 and 400 ppm concentrations. Application of consortium in soil spiked with chlorpyrifos enhanced all the biometric characters and reduced the residue of chlorpyrifos. The study also established efficient colonization of the chlorpyrifos degraders present in the consortium in the rhizosphere of cowpea.