Respuesta microbiana al tratamiento con 2,4-D en ensayo de microcosmos

CUADRADO, V; MERINI, LJ; FLOCCO, CG; GIULIETTI, AM

Valparaiso - Chile

Congreso; XXVI Congreso Chileno de Microbiología.; 2004

Phenoxy herbicides are widely employed in agriculture. Due to their physicochemical properties and extensive use there is a great risk of soil and water contamination. In order to evaluate the possibility of bioremediation of contaminated soils with the indigenous microflora and the influence of alfalfa plants on this degradation, we carried out a microcosm assay using soil with history of 2,4-DB treatment. Different sets of sterile, non-sterile, planted, non-planted, with/without herbicide microcosms were established. In this way, we could differentiate the contribution of soil microbes and plants on the degradation of the herbicide. The experimental units consisted in 360 ml glass flasks with 100 gr of soil, with or without alfalfa plants. 2,4-D was used as herbicide, and samples were taken at 0, 1, 5, 15 and 30 days since its addition. The evaluated parameters were: residual amounts of herbicide by soil extraction and HPLC analysis; total heterotrophic bacteria counts on R2A agar plates; and 2,4-D degrading bacteria counts by a Most Probable Number assay relying on herbicide degradation. We observed a rapid dissipation of the herbicide in all the treatments (total disappearance after 1 day) and the presence of 2,4-DCP (main metabolite) at time 0, especially in planted microcosms. The total heterotrophic bacteria population in bulk soil was about 10exp8 CFU/gr dry soil in every treatment and an increment of these numbers was observed after 2,4-D addition either for planted and unplanted microcosms (1 order of magnitude after 15 days). Regarding 2,4-D degrading bacteria, there was a 2 orders of magnitude increment in the size of this population after herbicide addition, from time 0 to day 15. This behavior was similar in planted and unplanted microcosms. A preliminary conclusion is that the herbicide addition increases the numbers of 2,4-D degrading and total bacteria counts, and that plants don’t influence on 2,4-D degradation by indigenous microflora. However, a more exhaustive study must be performed in order to correlate the herbicide dissipation with bacterial counts and to explore plant-bacteria interactions. Evaluating the capability of herbicide degradation by soil microbes and the factors that influence on it is a necessary step for future design of bioremediation strategies. Supported by grant ICA4-CT-2002-10011, European Community