Isolation of atrazine degrading bacteria from agricultural soils in Argentina

CUADRADO, V; MERINI, LJ; GIULIETTI, AM

Cordoba - Argentina

Congreso; Congreso Argentino de Microbiología; 2007

Asociación Argentina de Microbiología

Triazinic herbicides (atrazine) have been widely employed in agricultural fields for weed control. Their physicochemical properties and extensive use increase the risk of soil and water contamination. The attenuation of these herbicides in soils is mainly achieved by microbial degradation. In this way, selection of microorganisms with the ability to degrade pesticides from a particular ecosystem is the main step in bioremediation research. The purpose of this work was the enrichment, isolation and characterization of microorganisms able to degrade atrazine, from agricultural fields of Argentinean Humid Pampa region, with 20 years of atrazine application. Enrichments in liquid culture were established, using atrazine as sole N source, sole C source, C and N source, or as additional C and/or N source. In this way, it was possible to isolate a great diversity of herbicide degrading bacteria. The liquid enrichments were subcultured several times, after analysis of atrazine degradation by HPLC and then isolations were carried out in solid medium. Thirty microbial strains were purified and genetically characterized by sequencing the 16S rDNA gene. Enrichment and characterization of catabolic microbial associations was also carried out, as they are useful in bioremediation strategies. The growth and catabolic performance of the pure bacteria strains and the microbial associations were determined in liquid media with different atrazine concentrations, and kinetic parameters were calculated for each case. Microbial growth was followed by OD at 600nm and atrazine and its main metabolites (desethyl-atrazine and desisopropyl-atrazine) were detected by HPLC. Analysis of a 500 nucleotides fragment of the 16S rDNA gene showed that 63% of the isolates belonged to the phylum Proteobacteria (mainly Alpha-proteobacteria), 30% were Actinobacteria and 7% Firmicutes. Three different bacteria associations resulted to be the more efficient in atrazine degradation, with 100% removal of the herbicide at a concentration range between 25 and 500 ppm, although with different degradation rates. Appearance of others atrazine metabolites was detected in consortia 7g1, but their identity is currently being investigated. Conclusions: The agricultural soil from Argentinean Humid Pampa with history of atrazine application contained indigenous herbicide degrading microbial communities. Identification of the isolates showed a great microorganisms diversity. Herbicide degradation was facilitated by the combined activities of consortia members, due to their synergistic enzymatic activities that make it possible to growth with atrazine even as sole C and N source. These cultivable microorganisms become potential candidates for bioremediation trials, including bioaugmentation strategies.