Investigation of potential rhizospheric isolate for cypermethrin degradation

Abstract

Rhizoremediation is the use of plant-microbe interaction for the enhanced degradation of contaminants. Rhizosphere bioremediation of pyrethroid pesticides will offer an attractive and potentially inexpensive approach for remediation of contaminated soil. The present study was done with the aim of establishment of highly effective remediation method using plant with degradative rhizosphere and isolation of naturally occurring rhizosphere associated potential degrader providing the possibility of both environmental and insitu detoxification of cypermethrin contamination. The remediation efficacy of Pennisetum pedicellatum was investigated using green house pot culture experiments in cypermethrin amended potting soil mix (10, 25, 50, 75 and 100 mg/kg) for periodic evaluation of changes in concentration. Total proportion of cypermethrin degraders was found to be higher in rhizosphere soil compared to bulk soil. The cypermethrin degrading strain associated with rhizosphere capable of surviving at higher concentrations of cypermethrin was designated as potential degrader. On the basis of morphological characteristics, biochemical tests and 16S rDNA analysis, isolate was identified as Stenotrophomonas maltophilia MHF ENV 22. Bioremediation data of cypermethrin by strain MHF ENV22 examined by HPLC and mass spectroscopy, indicated 100, 50 and 58 % degradation within the time period of 72, 24 and 192 h at concentrations 25, 50 and 100 mg/kg, respectively. This is the first report of effective degradation of cypermethrin by Stenotrophomonas spp. isolated from rhizosphere of Pennisetum pedicellatum. Rhizoremediation strategy will be of immense importance in remediation of cypermethrin residues to a level permissible for technogenic and natural environment.

Keywords: Cypermethrin; Rhizoremediation; Soil; Stenotrophomonas maltophilia MHF ENV 22.

Fig. 1

First order reaction kinetics of rhizospheric dissipation of cypermethrin

Fig. 2

Percentage degradation of cypermethrin during rhizoremediation by P. pedicellatum

Fig. 3

Phylogenetic tree of potential degrader isolated from rhizoremediated soil (based on 16S rDNA sequence analysis). Unknown refers to S. maltophilia MHF ENV 22, the current strain reported in this study

Fig. 4

Concentration of cypermethrin during bioremediation by S. maltophilia MHF ENV 22

Fig. 5

Measurement of optical density (OD) at 600 nm during cypermethrin bioremediation by S. maltophilia MHF ENV 22

Fig. 6

Biological oxygen demand (BOD) variations during cypermethrin bioremediation by S. maltophilia MHF ENV 22

Fig. 7

Chemical oxygen demand (COD) variations during cypermethrin bioremediation by S. maltophilia MHF ENV 22