MONITORING IMPACT OF A PESTICIDE TREATMENT ON BACTERIAL SOIL COMMUNITIES BY METABOLIC AND GENETIC FINGERPRINTING IN ADDITION TO CONVENTIONAL TESTING PROCEDURES

Herbogil (dinoterb), a reference herbicide, the mineral oil Oleo (para ffin oil used as an additive to herbicides), and Goltix (metamitron) m ere taken as model compounds for the study of impacts on microbial soi l communities. After the treatment of soil samples, effects on metabol ic sum parameters were determined by monitoring substrate-induced resp iration (SLR) and dehydrogenase activity, as well as carbon and nitrog en mineralization. These conventional ecotoxicological testing procedu res are used in pesticide registration. inhibition of biomass-related activities and stimulation of nitrogen mineralization were the most si gnificant effects caused by the application of Herbogil. Even though G oltix and Oleo were used at a higher dosage (10 times higher), the app lication of Goltix resulted in smaller effects and the additive Oleo w as the least-active compound, with minor stimulation of test parameter s at later observation times. The results sen ed as a background for i nvestigation of the power of ''fingerprinting'' methods in microbial e cology. Changes in catabolic activities induced by treatments were ana lyzed by using the 95 carbon sources provided by the BIOLOG system. Va riations in the complex metabolic fingerprints demonstrated inhibition of many catabolic pathways after the application of Herbogil. Again, the effects of the other compounds were expressed at much Ion er level s and comprised stimulations as well as inhibitions. Testing for signi ficance by a multivariate t test indicated that the sensitivity of thi s method was similar to the sensitivities of the conventional testing procedures. The variation of sensitive carbon sources, as determined b y factor weights at different observation times, indicated the dynamic s of the community shift induced by the Herbogil treatment in more det ail. DNA extractions from soil resulted in a collection of molecules r epresenting the genetic composition of total bacterial communities. Di stinct and highly reproducible community patterns, or genetic fingerpr ints, resulting from application of the different herbicides were obta ined by the sequence-specific separation of partial 16S rDNA amplifica tion products in temperature gradient gel electrophoresis. Significant pattern variations were quantified. For detailed analysis, applicatio n-responsive bands from the Herbogil and Oleo treatments were sequence d and their tentative phylogenetic positions were identified. Data int erpretation and the potentials and biases of the additional observatio n windows on microbial communities are discussed.