Volume No. 9 Issue No.: 4 Page No.: 1138-1149 April-June 2015

 

PLANT GROWTH PROMOTING RHIZOBACTERIA : AN EFFECTIVE TOOL TO REMEDIATE RESIDUAL ORGANOPHOSPHATE PESTICIDE METHYL PARATHION, WIDELY USED IN INDIAN AGRICULTURE

 

Yadav Pratibha and Sundari S. Krishna*

Department of Biotechnology, Jaypee Institute of Information Technology (JIIT), NOIDA, U.P. (INDIA)

 

Received on : February 10, 2015

 

ABSTRACT

 

Organophosphate pesticides (OPP) are applied globally and are considered to be relatively safer alternatives to the first generation pesticides dominated by organochlorines. OPP are also more amenable to degradation. However, bioaccumulation of highly toxic organophosphates (Ops) has been observed which may be due to sorption of OPs to soil particles, making it unavailable for microbial metabolism. As a result several acute and chronic toxicity effects (Neurological effects) were reported in connection with OPP. The primary route of entry of these chemicals to food chain is through food crops grown in chemically overburdened agricultural soils. Hence its important to address this problem by constructing a bioremediation method for in-situ remediation of OPP in agricultural soils without causing any harm to plants. Our study focuses on remediation of OPP methyl parathion using rhizobacteria (namely RB1, RB2, RB3 and RB4) that also have properties of plant growth promotion. Primary screening was done to check the limits of tolerance in test isolates to a range of OPP (100 - 600ppm). Isolate RB1 showed best tolerance to OPP with a11% growth increment at 500ppm of OPP. In order to test the capability of these isolates to utilize OPP as principle carbon and/or nitrogen source, in vitro experiments were conducted by sequential exclusion of carbon and nitrogen salts in the medium and provision of OPP in their place. Amongst the four isolates studied, RB1 was found to be best utiliser of methyl parathion as both carbon and nitrogen source followed by RB4, whereas RB3 showed best response towards utilization of methyl parathion as nitrogen source. Further enzyme assays were conducted to test the presence of enzymes responsible for OPP degradation i.e., estrase and OPhydrolase (OPH). Isolates RB1 and RB4 showed maximum enzyme activity even at a OPP concentration of 300ppm. Additionally biochemical tests were performed to identify such properties that would increase OPP bioavailability and thus promote degradation of OPP. These assays comprised of: emulsification assay, assay for biofilm formation and biosurfactant assay to which isolates RB1, RB2 and RB3 gave strong positive results. Subsequently, in vitro plant bioassay was performed to check ability of these isolates for promoting growth of Mung bean (Vigna radiata) when challenged with increasing concentrations of OPP (100 500ppm) in the medium. Upon inoculation with test isolates, positive growth increment was observed in radical length and an increase in percentage germination, leaf count, seed vigour and total biomass in seedlings. Thus from our study it is evident that rhizobacteria can be effectively used both for remediation of OPP and promote plant growth.

 

Keywords : Pesticide remediation, Esterase, OP hydrolase, Rhizobacteria, Biofilm

 

 

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