Indexed on: 08 Aug '19Published on: 07 Aug '19Published in: Environmental Science & Technology
2,6-dichlorobenzamide (BAM) is a major groundwater micropollutant posing problems for drinking water treatment plants (DWTPs) that depend on groundwater intake. Aminobacter sp. MSH1 uses BAM as a sole source of carbon, nitrogen and energy and is considered a prime biocatalyst for groundwater bioremediation in DWTPs. Its use in bioremediation requires knowledge on its BAM-catabolic pathway which is currently restricted to the amidase BbdA converting BAM into 2,6-dichlorobenzoic acid (2,6-DCBA) and the mono-oxygenase BbdD transforming 2,6-DCBA in 2,6-dichloro-3-hydroxybenzoic acid. Here, we show that the 2,6-DCBA catabolic pathway is unique and differs substantially from catabolism of other chlorobenzoates. BbdD catalyses a second hydroxylation forming 2,6-dichloro-3,5-dihydroxybenzoic acid. Subsequently, glutathione-dependent dehalogenases (BbdI and BbdE) catalyse the thiolytic removal of a first chlorine. The remaining chlorine is then removed hydrolytically by a dehalogenase of the / hydrolase superfamily (BbdC). BbdC is the first enzyme in that superfamily associated with dehalogenation of chlorinated aromatics and appears to represent a new subtype within the / hydrolase dehalogenases. The activity of BbdC yields a unique trihydroxylated aromatic intermediate for ring cleavage that is performed by an extradiol dioxygenase (BbdF) producing 2,4,6-trioxoheptanedioic acid which is likely converted to Krebs cycle intermediates by BbdG.