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Identification of an Indigenous Atrazine Herbicide Tolerant Microbial Consortium in Beans (Phaseolus vulgaris L.) as a Potential Soil Bioremediator

Margarita Islas-Pelcastre, Jose Roberto Villagómez-Ibarra, Blanca Rosa Rodríguez-Pastrana, Gregory Perry, Alfredo Madariaga-Navarrete

The present article reports the isolation and identification of atrazine-tolerant strains of indigenous microorganisms recovered from three representative agricultural sites representing agronomic characteristics of the Tulancingo Valley, Central part of México (disturbed and undisturbed). Biochemical and morphological tests were performed for microorganism’s identification and the minimum inhibitory concentration assay was followed to assess atrazine tolerance. Results showed the microorganism populations varied from 10-5 to 10-6 UFC g-1 of soil for bacteria and 104 - 105 conidia g-1 of soil for fungi. The bacterial genera isolated and identified were: Agrobacterium sp., Bacillus sp., Erwinia sp., Micrococcus sp., Pediococcus sp., Rhizobium sp., Serrantia sp. and Sphingomonas sp. Identified fungal genera were: Alternaria sp., Aspergillus sp., Mucor sp., Cladosporium sp., Penicillium sp., Fusarium sp. and Trichoderma sp. Tests for herbicide tolerance indicate the isolated microorganisms do not show inhibitory growth at 500 to 2,500 ppm of atrazine concentrations under laboratory conditions. The strains of the fungal genera and Rhizobium sp. showed greater tolerance rates to atrazine, based on their growth without inhibition in the presence of 5,000 to 10,000 ppm of the agrochemical. Results suggest the isolated microorganisms may be useful as a viable inoculum for bioremediation purposes in agricultural atrazine-contaminated soils.