Biodegradation of Chlorinated s-Triazines

The catabolism of chlorinated s-triazines, e.g., herbicides, is incompletely understood. The first demonstration of their quantitative microbial degradation is the fungal dealkylation of simazine (CEET [for meaning of abbreviations throughout, see Table 1, footnote a]) to two major products, deethylsimazine (CEAT; two-thirds of total) and an unidentified s-triazine (one-third of total) (11, 12). This latter product is tentatively identified as CAAT (see Fig. 1) (2), and both products are observed in soils treated with CEET (see reference 13). CEAT and CAAT in soil are presumed to be biological products, in contrast to hydroxysimazine (EEOT), which can be formed by nonbiological catalysis on clay surfaces (see reference 9). Nonquantitative degradation of atrazine (CIET) to a product which hydrolyzes spontaneously is also known (7, 8). CEAT is quantitatively utilized as a nitrogen source by a strain of Rhodococcus corallinus, yielding EOOT, which is utilized quantitatively in coculture with a pseudomonad to yield cell material (A. M. Cook and R. Hutter, J. Agric. Food Chem., in press). CAAT is subject to partial ring cleavage in soil (40% in 192 days), but the organism(s) responsible is unknown (16). We now report that Pseudo-