Microbial response and factors influencing 2,4-DB biodegradation in a microcosms assay

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

Pinamar - Buenos Aires

Congreso; XLI Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (S.A.I.B.).; 2005

Phenoxy herbicides such as 2,4-DB (2,4-dichlorophenoxybutyric acid) are widely employed in agriculture. Although their half life in soil is relatively short, the excessive use leads to contamination of water courses, which represents a serious risk for human health and wildlife. In order to evaluate the biodegradation capability of soil microbial communities and the factors that influence on it (including plant-bacteria interactions), a microcosm assay was carried out. The main objectives were to study the response of soil bacteria to different doses of 2,4-DB, the catabolic performance of  indigenous microbial communities of soils with and without history of herbicide use, and also the effect of alfalfa plants on these processes. In this way, different sets of increasing complexity microcosms were set up and microbial populations, including total and 2,4-DB degrading bacteria, herbicide dissipation and plant parameters were evaluated in every sampling time. The results showed a high correlation between the herbicide dissipation curve and the shifts in bacteria numbers in all the treatments. It was observed the high adaptation of the microflora in soil with history of herbicide use and also how the bacteria counts grew up after 2,4-DB addition in all the cases (with different rates and final numbers depending the treatment). Regarding plants, they did not seem to enhance the numbers of 2,4-DB degraders nor the herbicide dissipation. Knowing the influence of all these factors on herbicide degradation, represents a necessary step for the design of bioremediation strategies.