Appl Microbiol Biotechnol (2005) 69: 321–325 DOI 10.1007/s00253-005-1983-5 APPLIED MICROBIAL AND CELL PHYSIOLOGY Thammajun Leungsakul . Brendan G. Keenan . Barth F. Smets . Thomas K. Wood TNT and nitroaromatic compounds are chemoattractants for Burkholderia cepacia R34 and Burkholderia sp. strain DNT Received: 2 January 2005 / Revised: 27 March 2005 / Accepted: 31 March 2005 / Published online: 26 April 2005 # Springer-Verlag 2005 Abstract Nitroaromatic compounds are toxic and poten- tial carcinogens. In this study, a drop assay was used to detect chemotaxis toward nitroaromatic compounds for wild-type Burkholderia cepacia R34, wild-type Burkhol- deria sp. strain DNT, and a 2,4-dinitrotoluene (2,4-DNT) dioxygenase mutant strain (S5). The three strains are che- motactic toward 2,4,6-trinitrotoluene (TNT), 2,3-DNT, 2, 4-DNT, 2,5-DNT, 2-nitrotoluene (NT), 4NT, and 4-meth- yl-5-nitrocatechol (4M5NC), but not toward 2,6-DNT. Of these, only 2,4-DNT is a carbon and energy source for B. cepacia R34 and Burkholderia sp. strain DNT, and 4M5NC is an intermediate in the 2,4-DNT degradation pathway. It was determined that the 2,4-DNT dioxygenase genes are not required for the chemotaxis for these nitro- aromatic compounds because the DNT DDO mutant S5 has a chemotactic response toward 2,4-DNT although 2,4- DNT is not metabolized by S5; hence, 2,4-DNT itself is the chemoattractant. This is the first report of chemotaxis to- ward TNT, 2,3-DNT, 2,4-DNT, 2,5-DNT, 2NT, 4NT, and 4M5NC. Introduction The enzymes and genetic pathways required for bacterial degradation of toxic organic compounds such as polychlo- rinated biphenyls, toluene, naphthalene, and nitroaromatic compounds have been determined (Grimm and Harwood 1997; Samanta et al. 2000; Parales and Harwood 2002). However, the role of chemotaxis in pollutant biodegrada- tion and bioremediation has not been studied extensively (Samanta et al. 2000; Parales 2004). Bacterial chemotaxis, movement due to a chemical gradient (Pandey et al. 2002), enhances biodegradation by bringing cells close to the pol- lutant thereby reducing poor bioavailability, sequestration of the chemical on surfaces, and low solubility (Parales and Harwood 2002). For example, chemotaxis by Pseudomo- nas putida G7 was shown to enhance naphthalene degra- dation compared to nonchemotactic and nonmotile mutants, proving chemotaxis can overcome these mass transfer prob- lems that may limit biodegradation rates (Marx and Aitken 2000; Law and Aitken 2003). Most nitroaromatic compounds in the environment are man-made and are released from manufacturing pharma- ceuticals, dyes, plasticizers, pesticides, and explosives (Spain 1995). Chemotaxis toward nitroaromatic compounds has been investigated previously as it has been reported that Ralstonia sp. SJ98 is chemotactic toward nitrocatechol, ni- trophenols, nitrobenzoate, dinitrobenzenes, dinitrophenols, and dinitrobenzoates (Bhushan et al. 2000; Samanta et al. 2000; Pandey et al. 2002). P. putida PRS2000 was also found to be chemotactic toward nitrobenzoates and amino- benzoates (Parales 2004). In this study, we focus on chemotaxis toward the ni- troaromatic compounds 2,4,6-trinitrotoluene (TNT), 2,3- dinitrotoluene (2,3-DNT), 2,4-DNT, 2,5-DNT, 2,6-DNT, 2-nitrotoluene (NT), 4NT, and 4-methyl-5-nitrocatechol (4M5NC). 2,4-DNT and 2,6-DNT are found in soil and groundwater as contaminants from the manufacture of TNT, the most common explosive (Nishino et al. 2000). 2,4-DNT and 2,6-DNT are also intermediates in the production of T. Leungsakul . B. G. Keenan . T. K. Wood (*) Departments of Chemical Engineering and Molecular and Cell Biology, University of Connecticut, Storrs, CT, 06269, USA e-mail: twood@engr.uconn.edu Tel.: +1-860-4862483 Fax: +1-860-4862959 B. F. Smets Departments of Civil and Environmental Engineering and Molecular and Cell Biology, University of Connecticut, Storrs, CT, 06269, USA B. F. Smets Environment and Resources, Technical University of Denmark, DK-2800 Lyngby, Denmark