Joined: May 2002
Atrazine degradation pathways appear to have arisen recently:
This lab studies 'em:
...Some of their papers are free online:
DeSouza, M. L., J. Seffernick, B. Martinez, and M. J. Sadowsky, L. P. Wackett (1998) Atrazine catabolism genes atzABC are widespread and highly conserved J. Bacteriol. 180(1):1951-1954.
De Souza, M. L., L. P. Wackett, and M. J. Sadowsky (1998) The atzABC genes encoding atrazine catabolism are located on a self-transmissible plasmid in Pseudomonas sp. strain ADP. Appl. Envir. Microbiol. 64(6): 2323-2326.
M.L. deSouza, D. Newcombe, S. Alvey, Crowley, D.E., A. Hay, M.J. Sadowsky, and L.P. Wackett (1998) Molecular basis of a bacterial consortium: Interspecies catabolism of atrazine. Appl. Environ. Microbiol. 64(1):178-184.
In the latter paper, it looks as if three different enzymes found in different bacteria were first combine in multispecies consortia that could metabolize atrazine, and that eventually the 3 genes were combined on a plasmid which then spread around the world in an evolutionary eyeblink. If this is basically what happened it is yet another method of producing IC (as well as new information).
Atrazine is the most widely used s-triazine herbicide; it is utilized globally to control broadleaf weeds. Atrazine has been deployed only over the last 40 years and was previously considered to be nonmetabolizable by the majority of soil bacteria. During the first 35 years of its use, bacterial atrazine catabolism was proposed to occur largely via N-dealkylation reactions, resulting in the accumulation of aminotriazine compounds in both soils and laboratory media (3-5, 11, 20, 21). More recently, pure cultures of bacteria that catabolize atrazine to CO2 have been described (8, 26, 27, 30, 37).
The nearly simultaneous reports of atrazine-mineralizing pure cultures by five research groups (8, 26, 27, 30, 37) after years of unsuccessful efforts suggested a recent evolutionary origin and distribution of atrazine degradation genes. Consistent with this, all of the recently identified atrazine-degrading bacteria, isolated from around the world, have been shown to contain similar genes that encode enzymes which catabolize atrazine to cyanuric acid (16) (see Fig. 1). Cyanuric acid can be used by many soil bacteria as the sole nitrogen source (10-12, 19, 23). The enzymes for atrazine catabolism to cyanuric acid are encoded by the atzABC genes, which are found on a self-transmissible plasmid in Pseudomonas sp. strain ADP, the best characterized atrazine-metabolizing bacterium studied at the molecular level (7, 16, 17, 26, 32). Moreover, multiple insertion sequence-like elements have been identified in DNA flanking the atz genes. These studies are beginning to yield insights into atrazine gene evolution and dispersion.
These data also provide the tools for investigating bacterial atrazine genes in situ or in microbial consortia cultured in the laboratory on atrazine. For example, an atrazine-catabolizing consortium was reported in 1994 (3), but that predated the identification of catabolic genes and pure cultures which metabolize atrazine to carbon dioxide. More recently, a stable aerobic consortium was obtained from an agricultural soil and characterized with respect to its ability to catabolize atrazine (1, 2).
The present study was conducted to determine whether the genes and metabolism of the consortium (1, 2) resembled those found in recently described atrazine-metabolizing pure cultures. Our results show that different consortium members separately contained the atzA, -B, and -C genes. Coupled with biochemical studies, this revealed the interspecies metabolic interactions relevant to atrazine catabolism by the consortium. Our findings begin to provide a framework for understanding how catabolic pathways may evolve and the different conditions under which pure-culture or consortial metabolism may be selected for during the global recycling of organic matter.
The present study extends previous work by demonstrating the individual metabolic and genetic contributions of consortium members that use a proposed recently evolved catabolic pathway (16). Atrazine and related s-triazine herbicides have been in commercial use for approximately 40 years. The wide use of s-triazine herbicides has led to their detection as contaminants in groundwater (6, 28, 29) and to point source soil contamination problems where these herbicides have been spilled. Previously, many isolates and mixed cultures that partially degrade atrazine have been found (3, 10); more recently, several bacterial pure cultures which can completely mineralize atrazine and other s-triazines have been isolated (8, 26, 27, 30, 37). In 1995, Mandelbaum et al. (26) isolated a single atrazine-mineralizing bacterium from a mixture of bacteria originally reported to be a consortium (24, 25), which suggested that the isolate arose from gene transfer which occurred in the mixed culture. The possibility of this has been heightened by our observation that the atzABC genes are located on a 96-kb plasmid, with at least two genes having flanking regions with high homologies to known insertion sequence elements (16). Thus, the present study may offer a window to the evolution of a catabolic pathway by beginning to reveal how genes move from a consortium to individual strains and how mixed cultures containing metabolically cooperating genes may be stably maintained.