Atrazine biodegradation

The atzA, atzB, and atzC genes - encoding enzymes necessary for the first three steps in atrazine biodegradation by Pseudomonas strain ADP - reside on a large, self-transmissible plasmid (de Souza et al., 1998a, b). 

Figure 1. Upper atrazine biodegradation pathway in all known atrazine-mineralizing bacteria showing hydrolytic conversion of atrazine to cyanuric acid. Dehalogenation of atrazine to 2-hydroxyatrazine is catalyze by the gene product of atzA. 2-Hydroxyatrazine is then sequentially AT-deaUcylated to produce cyanuric acid by enzymes encoded by atzB and atzC,...

The widely-used herbicide atrazine poses a threat to environmental health if point sources due to spills are not efficiently dealt with. Numerous atrazine-degrading microorganisms have been been isolated, and there is much known about the genetics and biochemistry of atrazine biodegradation. A variety of studies have e qilored the utility of atrazine-degrading bacteria for soil bioremediation. The effects of various rate controlling factors, pH, availability of nutrients, terminal electron acceptor and efficacy of different bacteria have been explored. Finally, the advent of molecular methods used to monitor the persistence and assess die activity of bioremediating bacteria is likely to inqirove the success of bioremediation. 

Figure 12.62, another possibility of atrazine biodegradation may be dealkylation on the secondary amino group at carbons C-4 and C-6. Dealkylated metabolites partly retain the herbicidal activity of the parent compound. 

A number of substituted triazines are used as herbicides, and their biodegradation has been discussed in Chapter 10, Part 1. Treatment of soil contaminated with atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-l,3,5-triazine) illustrated a number of significant features. Although the soil that was used had the potential for degradation, a laboratory experiment with Pseudomonas sp. strain ADP that had an established potential for atrazine degradation revealed important limitations. There was a substantial decline in the numbers of Pseudomonas sp. strain ADP and only limited mineralization. Supplementation with citrate or succinate increased the survival of the strain, and successful mineralization was dependent on the preservation of a carbon/nitrogen ratio >10 (Silva et al. 2004). The last would apply generally to substrates with a low C/N ratio such as triazines. 

Gu J, Fan Y, Gu J-D (2003a) Biodegradability of atrazine, cyanzine and dicamba under methanogenic conditions in three soils of China. Chemosphere 52 1515-1521... 

Wackett LP, Sadowsky MJ, Martinez B et al (2002) Biodegradation of atrazine and related s-triazine compounds from enzymes to field studies. Appl Microbiol Biotechnol 58 39—45... 

Alexander M (1977) Introduction to soil microbiology, 2nd edn. WUey, New York Alexander M (1980) Biodegradation of chemicals of environmental concern. Science 211 132-138 Armstrong DE, Chester G, Harris RF (1967) Atrazine hydrolysis in soil. Soil Sci Soc Am Proc... 

Groundwater. Atrazine dominated the world herbicide market in the 1980s, and contamination of groundwater has been reported in several locations in the U.S., Europe, and South Africa. Successful biodegradation has been achieved with indigenous organisms in laboratory mesocosms after a lag phase, and once activity was found, it remained, It is clear that intrinsic remediation is likely to lead to the disappearance of atrazine from groundwaters. 

Strothers, J.K., K. Jayachandran, and T.B. Moorman (1998). Biodegradation of atrazine by Agrobacterium radiobacter J14a and use of this strain in bioremediation of contaminated soil. Appl. Environ. Microbiol., 64 3368-3375. 

Figure 22.2 Plate assay for examining the biodegradation of atrazine.3...

Radosevich et al. (1995b) studied the biodegradation of binary and ternary mixtures of atrazine, simazine, and cyana-zine using a pure culture of the atrazine-degrading bacterium Ralstonia pickettii (previously strain M91-3). While the bacterium used atrazine and simazine indiscriminately, cyanazine degradation was slow and delayed until the depletion of the two other herbicides. There was no apparent effect of other commonly used herbicides on the rate of atrazine... 

Alvey, S. and D.E. Crowley (1995). Influence of organic amendments on biodegradation of atrazine as a nitrogen source. J. Environ. Qual., 24 1156-1162. 

Radosevich, M., S.J. Traina, and O.H. Tuovinen (1996). Biodegradation of atrazine in surface soils and subsurface sediments collected from an agricultural research farm. Biodegradation, 1 137-149. 

Wackett, L.P., M.J. Sadowsky, B. Martinez, and N. Shapir (2002). Biodegradation of atrazine and related. v-triazine compounds From enzymes to field studies. Appl. Microbiol. Biotechnol., 58 39-45. 

Kearney, PC., M.T. Muldoon, C. Somich, J.M. Ruth, and D.J. Voaden (1988). Biodegradation of ozonated atrazine as a wastewater disposal system. J. Agric. Food Chem., 36 1301-1306. 

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