Biodiversity of organophosphorus-degrading bacteria isolated from agricultural soils

Abstract

Organophosphorus (OP) insecticides are used all over the world for crop protection. Although OPs are less persistent than organochlorine pesticides, they still constitute an environmental risk thus increasing the social concern about their levels in soils, surface and ground waters. Biodegradation by microorganisms is primarily responsible for elimination of the OP insecticides released to the environment. In the present study the OP degrading potential of agricultural soils with different agronomic history was investigated. Using enrichment cultures, with parathion or dimethoate as the sole C and energy sources, 47 bacterial isolates were obtained from OPs contaminated and pristine agricultural soils characterized by different physico-chemical properties. The isolates were grouped into 17 Operational Taxonomic Units (OTU) by analysis of the ribosomal internal transcribed spacer (ITS) polymorphisms. All the soils showed the presence of putative OPs degraders: the highest diversity was found in organically cultivated soils under Citrus groves, the lowest in chemically cultivated soils. Partial sequencing of 16S rRNA gene of representative isolates of each OTU revealed that most of them belong to Proteobacteria and Actinobacteria. Degradation of parathion was confirmed by SPME GC-MS analysis. Some strains belong to genera or species that are currently unknown as OPs degraders. Investigation on the degradation genes using degenerated primers targeted to known organophosphorus hydrolase genes is in progress.