DEGRADATION OF ATRAZINE IN LABORATORY MICROCOSMS - ISOLATION AND IDENTIFICATION OF THE BIODEGRADING BACTERIA

Several natural ecosystems, including soil and water microcosms, have been explored for their potential to biodegrade atrazine 4-[ethylamino ]-6-[isopropylamino]-1,3,5-triazine). Subculturing soil or water sampl es with several applications of the herbicide leads to an enhancement of atrazine catabolism correlating with a decrease in the number of ba cterial species. A combination of enrichment culture techniques, the i mposition of carbon limitation, and plating on selective atrazine-agar plates have permitted the isolation of several bacteria able to biode grade atrazine from different polluted or unpolluted ecosystems. One o f the selected bacteria, originating from an agricultural soil, has be en identified as Acinetobacter calcoaceticus, which alone in pure cult ure can degrade atrazine. From another agricultural soil Pseudomonas a lcaligenes associated with an Agrobacterium sp. was selected. A garden soil treated only once with the herbicide was found to contain an ass ociation of five different bacteria that together degrade atrazine. Fi nally, a Pseudomonas putida/Xanthomonas maltophilia pair has been isol ated from an aquatic ecosystem. In consortium, in coculture, or in pur e culture with well-defined experimental parameters, the induced bacte ria degrade added atrazine in 18 h.