Isolation and characterization of newatrazine degrading bacterial strains and consortia from Argentinean agricultural soils

CUADRADO, V; MERINI, LJ; MOORE, E; GIULIETTI, AM

Dalian - China

Simposio; IBS2008; 2008

Triazinic herbicides have been widely employed in agriculture. Their physicochemical properties and extensive use increase the risk of soil andwater contamination (U.S. Environmental Protection Agency, 1990). Selection of microorganisms able to degrade pesticides from a particular ecosystem is the main step in bioremediation research (Alvey and Crowley, 1996; Rousseaux et al., 2001). 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 having previous long-term exposure to the herbicide. Enrichments in liquid culture were established, using atrazine as sole N and/or C source. Thirty microbial strains were purified and characterized genotypically by comparative sequence analysis of the 16S rRNA gene. Characterization of catabolic microbial associations was also carried out. Results showed that 63% of the isolates belonged to the Proteobacteria (mainly alpha-proteobacteria), 30% were Actinobacteria and 7% Firmicutes. Three different bacterial associations were the more efficient in degradation, with 100% removal at concentrations between 25 and 500 ppm, although with different degradation rates. Consortium 7G1 showed the highest rate, with 100% atrazine removal (sole C and N source) after 40–70 h. 7G1 is constituted by two bacterial strains which showed phylogenetic relationships with species of the genera Microbacterium (7G1 I) and Nocardioides (7G1 II). 7G1 I was not able to grow, using atrazine as sole N source, but it grew using OH-atrazine. 7G1 II was able to grow with atrazine or OH-atrazine, demonstrating that it is responsible for the first enzymatic step in atrazine degradation. Another work (Topp et al., 2000) indicated that some Nocardioides species harbor a catabolic pathway that begins with atrazine dechlorination. Thus, we could not detect the presence of chlorinated atrazine metabolites. Herbicide degradation was facilitated by the combined activities of consortia members, due to their synergistic enzymatic activities. These cultivable microorganisms become potential candidates for bioremediation trials. References Alvey, S., Crowley, D.E., 1996. Survival and activity of an atrazine mineralizing bacterial consortium in rhizosphere soil. Environ. Sci. Technol. 30, 1596–1603. Rousseaux, S., Hartmann, A., Soulas, G., 2001. Isolation and characterisation of new Gram-negative and Gram-positive atrazine degrading bacteria from different French soils. FEMS Microbiol. Ecol. 36, 211–222. Topp, E., Mulbry, W.M., Zhu, H., Tour, S.M., Cuppels, D., 2000. Characterization of s-triazine herbicide metabolism by a Nocardioides sp. isolated from agricultural soils. Appl. Environ. Microbiol. 66, 3134–3141. Summary results of EPA’s national survey of pesticides in drinkingwaterwells. 1990. U.S. Environmental Protection Agency, Office of Pesticides and Toxic Substances, pp. 16. U.S. GPO,Washington, DC. doi:10.1016/j.jbiotec.2008.07.1582