Real-time reverse transcription PCR analysis of expression of atrazine catabolism genes in two bacterial strains isolated from soil Marion Devers, Guy Soulas, Fabrice Martin-Laurent * INRA-CMSE, UMR 1229 INRA-Universite ´ de Bourgogne, Microbiologie et Ge ´ochimie des Sols, 17 rue Sully, BP 86510, F-21065 Dijon Cedex, France Received 20 June 2003; received in revised form 29 August 2003; accepted 29 August 2003 Abstract The level of expression of highly conserved, plasmid-borne, and widely dispersed atrazine catabolic genes (atz) was studied by RT-qPCR in two telluric atrazine-degrading microbes. RT-qPCR assays, based on the use of real-time PCR, were developed in order to quantify atzABCDEF mRNAs in Pseudomonas sp. ADP and atzABC mRNAs in Chelatobacter heintzii. atz gene expression was expressed as mRNA copy number per 10 6 16S rRNA. In Pseudomonas sp. ADP, atz genes were basally expressed. It confirmed atrazine-degrading kinetics indicating that catabolic activity starts immediately after adding the herbicide. atz gene expression increased transitorily in response to atrazine treatment. This increase was only observed while low amount of atrazine remained in the medium. In C. heintzii, only atzA was basally expressed. atzA and atzB expression levels were similarly and significantly increased in response to atrazine treatment. atzC was not expressed even in the presence of high amounts of atrazine. This study showed that atz genes are basally expressed and up-regulated in response to atrazine treatment. atz gene expression patterns are different in Pseudomonas ADP and C. heintzii suggesting that the host may influence the expression of plasmid-borne atrazine-catabolic potential. D 2003 Elsevier B.V. All rights reserved. Keywords: Atrazine; Biodegradation; atz gene; RT-qPCR; Gene expression 1. Introduction Atrazine (2-chloro-4-ethylamino-6-isopropyla- mino-s-triazine) has been one of the world’s most heavily used agricultural herbicides during the past 30 years to control a variety of broadleaf weeds colonis- ing corn, sugarcane, sorghum, pineapple and other crops. Atrazine is moderately persistent in natural environments, with a half-life ranging from a few days to several months (Solomon et al., 1996). It is slowly degraded to hydroxyatrazine by chemical pro- cesses (Ma and Selim, 1996) and partially hydroxyl- ated to deethylatrazine (DEA) and deisopropylatrazine (DIA) by endogenous bacterial monooxygenases (Barriuso et al., 1996). As a result, atrazine and its two main metabolites (DEA and DIA) are often detected in surface water, tile drainage and ground water at concentrations exceeding the European Union standard of 0.1 Agl  1 (Spliid and Koppen, 1998). Soils repeatedly treated with atrazine show enhanced atrazine degradation resulting in its miner- 0167-7012/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.mimet.2003.08.015 * Corresponding author. Tel.: +33-3-80-69-34-06; fax: +33-3- 80-69-32-24. E-mail address: fmartin@dijon.inra.fr (F. Martin-Laurent). www.elsevier.com/locate/jmicmeth Journal of Microbiological Methods 56 (2004) 3 – 15