Isolation of an acetochlor detoxifying bacterium and cloning of an associated gene.

Abstract

A Pseudomonas strain, AI08, which was capable of detoxifying the herbicide acetochlor (2- chloro-N-ethoxymethyl-6'-ethylacet-o-toluide) was isolated from soils. The microbe was isolated using a combination of batch culture enrichment techniques, phenotypic agar plate based assays and a qualitative bioassay for detecting acetochlor detoxification. With the aid of a bioassay developed specifically for the quantification of acetochlor concentrations, it was determined that over a 21 day period Al 08 was capable of detoxifying 20 % of the acetochlor present in a medium containing no other organic carbon and 53 % of the herbicide in a medium containing glucose and yeast extract at concentrations of 0.02 g.l-l and 0.005 g.l-l respectively. A fragment of A108 DNA was cloned in Escherichia coli which produced recombinant cells with both elevated acetochlor resistance and the ability to detoxify 15 % of the acetochlor present in a minimal nutrient medium (containing 0.02 g.l-l glucose and 0.005 g.l-l yeast extract) over a 21 day period. Partial sequencing of the cloned A108 DNA revealed that it encoded an amino acid sequence with significant homology with the dihydrolipoyltransacetylase component of the pyruvate dehydrogenase complexes of Azotobacter vinlandii, E. coli and Alcaligenes eutrophus. Theories are proposed as to the possible biochemical mechanisms whereby expression of the dihydrolipoyltransacetylase gene of Al 08 in recombinant E. coli cells may function in the detoxification of acetochlor.