The potential of a novel β-specific dehalogenase from Bacillus cereus WH2 as a bioremediation agent for the removal of β-haloalkanoic acids

Aims: This study aims to describe the biochemical and kinetic properties of a dehalogenase produced by a bacterium, Bacillus cereus WH2 (KU721999), that is uniquely adept at degrading a -haloalkanoic acid, i.e., 3-chloropropionic acid (3-CP), and using it as the bacterium's sole carbon source. The bacterium was isolated from abandoned agricultural land in Universiti Teknologi Malaysia that was previously exposed to herbicides and pesticides. Methodology and results: The B. cereus impressively removed 97% of 3-CP after 36 h of culturing. The intracellular WH2 dehalogenase of the bacterium was purified 2.5-fold and has an estimated molecular mass of 37 kDa. The highest activity of the dehalogenase was achieved under conditions of 30 C and pH 7. The metal ions Hg 2+ and Ag 2+ substantially repressed the enzyme's activity, but the enzyme's activity was uninhibited by dithiothreitol (DTT) and EDTA. The WH2 dehalogenase showed a higher affinity for 3-CP (Km = 0.32 mM, kcat = 5.74 s -1 ) than for 3-chlorobutyric acid (3-CB) (Km = 0.52 mM; kcat = 5.60 s -1 ). The enzyme was ~1.6-fold more catalytically efficient (kcat/Km) in dehalogenating the three-carbon substrate 3-CP (17.8 mM -1 s -1 ) than the four-carbon 3-CB (11.2 mM -1 s -1 ).