Annals of Microbiology, 59 (3) 447-451 (2009) Degradation of 3-chloropropionic acid (3CP) by Pseudomonas sp. B6P isolated from a rice paddy field Suhailysa MESRI 1 , Roswanira Ab. WAHAB 2 , Fahrul HUYOP 1* 1 Industrial Biotechnology Department, Faculty of Biosciences & Bioengineering, University Technology Malaysia; 2 Chemistry Department, Faculty of Science, University Technology Malaysia, 81310 Skudai, Johor, Malaysia Received 12 May 2009 / Accepted 1 July 2009 Abstract - A bacterium that degrades 3-chloropropionic acid (3CP) was isolated from local paddy (rice) agricultural soil by enrichment culture. Taxonomic analysis identified the strain as Pseudomonas sp. Strain-mediated degradation of 3CP released chloride ions into the growth medium, and the degradation of ~100% of 20 mM 3CP was monitored by high performance liquid chromatography (HPLC). The putative Pseudomonas sp. dehalogenase that released the chloride ions from 3CP was induced by growth of the bacterium in the presence of 3CP as the sole carbon source. The dehalogenase showed activity against a specific type of halogenated aliphatic acids, and the highest activity was obtained with 3CP. However, the enzyme could only remove halogen atoms from 3-carbon alkanoic acids if the halogen was at the β- but not the -position. In crude bacterial extracts, the dehalogenase activity with 3CP was maximum at 30 °C, over a broad pH range (pH 7.5 optimum) and had an apparent K ms of 0.25 ± 0.04 mM and 0.67 ± 0.17 mM for 3CP and 2,3-dichloropropionic acid, respectively. Key words: biodegradation; 3-chloropropionic acid; dehalogenase; bioremediation. INTRODUCTION Halogenated aliphatic compounds are widely used in agriculture and industry. These compounds are manufactured in large quan- tities and represent an important class of environmental pollut- ants due to their widespread use as herbicides, fungicides, insec- ticides, solvents, and hydraulic or transfer fluids (Fetzner and Lingens, 1994). These substances can be decontaminated using non-biological or microbiological degradation methods which transforms the xenobiotic substances into harmless products. However, microbiological methods are favoured because they are economical, safer and environmentally friendly. To date 18 halo- alkanoic acid dehalogenases from different bacteria have been isolated and characterised (Hill et al., 1999). Bacterial assimila- tion of these compounds is attributed to a group of enzymes called dehalogenases (Jensen, 1957). These dehalogenases are cluster in proteobacteria, in particular the and β and γ sub- phyla of this division (Marchesi and Weightman, 2003a). Some soil microorganisms can dehalogenate a wide range of chlorinated substrates via hydrolysis of the aliphatic carbon- halogen bond (Hardman, 1991; Slater et al., 1997). Several studies have indicated that certain bacteria contain a number of dehalogenases differing in their thermal stability, pH depend- ence, kinetic parameters, mechanism of dehalogenation, elec- trophoretic mobility, or inhibition by sulfhydryl-blocking agents (Kawasaki et al., 1981; Weightman et al., 1982; Slater et al., 1985). Previous studies have reported the identification of induc- ible dehalogenases in a soil bacterium that was capable of grow- ing on 2,2-dichloropropionic acid as its sole source of carbon and energy (Busto et al., 1992). There have been few reports on the degradation of β-chloro- substituted haloalkanoic acids such as 3-chloropropionic acid (3CP) (Hirsch and Alexander, 1960; McGrath and Harfoot, 1997). This compound is often included in pesticides or used as an inter- mediate for the synthesis of pharmaceuticals. It is carcinogenic and genotoxic to both animals and humans. This paper describes the identification and characterisation of a new type of dehalogenase activity from a bacterium isolated from a rice paddy field in Malaysia. Therefore, our research was to investigate the degradation of β-chloro-substituted haloalkanoic acid (3CP) using batch culture technique. This study would be useful in the bioremediation of chlorinated hydrocarbons and also to understand the diversity of dehalogenase enzyme functions. MATERIALS AND METHODS Chemicals. Various halogenated compounds of analytical grade were purchased from Sigma-Aldrich Chemical Co. (USA). * Corresponding Author. Phone: +607-553 4556; Fax: +607-556 6162; E-mail: fzhutm@gmail.com