Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Thu, 06 Dec 2018 06:24:23 Degradation of dichloroaniline isomers by a newly isolated strain, Bacillus megaterium IMT21 Xie-Feng Yao, 1,2 3 Fazlurrahman Khan, 3 3 Rinku Pandey, 2 Janmejay Pandey, 2,4 Roslyn G. Mourant, 2 Rakesh K. Jain, 3 Jian-Hua Guo, 1 Robyn J. Russell, 2 John G. Oakeshott 2 and Gunjan Pandey 2 Correspondence Gunjan Pandey Gunjan.Pandey@csiro.au Received 12 September 2010 Revised 8 December 2010 Accepted 9 December 2010 1 Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Key Laboratory of Monitoring and Management of Crop Diseases and Pest Insects, Ministry of Agriculture, Nanjing 210095, China 2 CSIRO Ecosystem Sciences, GPO Box 1700, Canberra, ACT 2601, Australia 3 Institute of Microbial Technology, Sector-39A, Chandigarh 160036, India 4 Institute of Biophysical Dynamics, Gordon Center for Integrative Sciences, University of Chicago, IL 60637, USA An efficient 3,4-dichloroaniline (3,4-DCA)-mineralizing bacterium has been isolated from enrichment cultures originating from a soil sample with a history of repeated exposure to diuron, a major metabolite of which is 3,4-DCA. This bacterium, Bacillus megaterium IMT21, also mineralized 2,3-, 2,4-, 2,5- and 3,5-DCA as sole sources of carbon and energy. These five DCA isomers were degraded via two different routes. 2,3-, 2,4- and 2,5-DCA were degraded via previously unknown dichloroaminophenol metabolites, whereas 3,4- and 3,5-DCA were degraded via dichloroacetanilide. INTRODUCTION Dichloroanilines (DCAs) are widely used intermediates in commercial syntheses of various azo dyes, herbicides, paints, cosmetics and other industrial chemicals. However, their stability and toxicity also render them hazardous when released into the environment (NTP Comparative Toxicity Studies, 1998; Argese et al., 2001; Lo et al., 1990; Padmanabhan et al., 2006). 3,4- and 3,5-DCA are particularly noxious, although 2,3-, 2,4- and 2,5-DCA are also highly toxic (Claver et al., 2006; Go ¨tz et al., 1998; Peng et al., 2005; Valentovic et al., 1995). 3,4-DCA is the most commonly used DCA isomer in the chemical industry (Giacomazzi & Cochet, 2004; Valentovic et al., 1995) and it is also the major breakdown product of the widespread phenylamide herbicides diuron, linuron and propanil. In fact it is detected more frequently in environmental samples than the parent herbicides (Claver et al., 2006; Giacomazzi & Cochet, 2004). Several bacterial strains have been isolated that can degrade 3,4-DCA, and at least one of these has also been reported to degrade 2,3- 2,4- and 2,5-DCA (Table 1). A complete degradation pathway has not been elucidated for 3,4-DCA, but 4-chloroaniline, 3-chloro-4-hydroxyaniline, 4-chloro- 3-hydroxyaniline, 4,5-dichlorocatechol and 1,2-dichloro- benzene have been suggested as intermediates, ultimately leading to mineralization via different catabolic routes (Table 1). Furthermore, 3,4-dichloroacetanilide, 3,39,4, 49-tetrachloroazobenzene and 3,4-dichloro-N-(3,4-dichlor- ophenyl)benzamide have also been reported as transforma- tion products or minor intermediates, suggesting that different degradation pathways could be operating in some of these strains (Table 1). In this communication we report the isolation of a new bacterial strain, Bacillus megaterium IMT21, which is able to mineralize five DCA isomers, 2,3-, 2,4-, 2,5-, 3,4- and 3,5-DCA, as sole sources of carbon and energy. We find that the catabolic pathway used depends on the isomer. 3,4- and 3,5-DCA are degraded via dichloroacetanilide, i.e. one of the previously reported pathways for 3,4-DCA. However, the other three isomers are degraded via previously undescribed dichloroaminophenol intermedi- ates. The mechanistic basis for this isomer-specific degradation is discussed. METHODS Chemicals. All DCA isomers, 3,4-dichloroacetanilide and formic acid were obtained from Sigma-Aldrich. Solvents were obtained from Merck. Abbreviation: DCA, dichloroaniline. 3These authors contributed equally to this work. The GenBank accession number for the 16S rRNA gene sequence reported in this paper is GU479395. Microbiology (2011), 157, 721–726 DOI 10.1099/mic.0.045393-0 045393 G 2011 CSIRO Printed in Great Britain 721