APPLICATION OF C-14-MOST-PROBABLE-NUMBER TECHNIQUE TO ENUMERATE ATRAZINE-DEGRADING MICROORGANISMS IN SOIL

The size and activity of atrazine-degrading populations are among the factors controlling atrazine persistence in soil. Populations of atraz ine-degrading microorganisms in surface and subsurface soils were enum erated by the C-14-most-probable-number (C-14-MPN) technique using [C- 14-ethyl]-atrazine or [U-C-14-ring]-atrazine in C-or N-limited media. The [C-14-ethyl] atrazine served as a potential carbon source for a la rger number of microorganisms than [U-C-14-ring]-atrazine. Populations of atrazine-degrading microorganisms using [C-14-ethyl]-atrazine as a carbon source ranged From 4670 to 31,930 cells g(-1) of surface soil, but were 1050 cells g(-1) in a subsurface sediment. The size of these [(14)-ethyl]-atrazine-degrading microbial populations were positively correlated (r(2)=0.81) to mineralization of [C-14-ethyl]-atrazine add ed to soil, which suggests that atrazine-degrading populations may ser ve as an indicator of atrazine persistence in the soil environment. Po pulations degrading [U-C-14-ring]-atrazine ranged from 130 to 1630 cel ls g(-1) soil in C-limited media and from 19 to 10,530 cells g-l soil in N-limited media. Population size and mineralization activity were g enerally increased by the frequency of atrazine use, suggesting that l ong-term exposure encourages microbial adaptation and growth. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.