Intermediate accumulation of metabolites results in a bottleneck for mineralisation of the herbicide metabolite 2,6-dichlorobenzamide (BAM) by Aminobacter spp.

Abstract

Degradation and mineralisation of the groundwater contaminant 2,6-dichloro-benzamide (BAM) was investigated in two Aminobacter strains focussing on the induction of BAM degradation and mineralisation and occurrence of intermediate metabolites. The BAM degradation rate was independent of whether the cells were pre-grown in the absence or presence of BAM, thus indicating that the first step in the degradation pathway was constitutively expressed. In contrast, (14)CO(2) production was stimulated when cells were pre-grown in the presence of BAM, suggesting that one or more of the subsequent steps in the degradation pathway were inducible. Accumulation of 2,6-dichlorobenzoate (DCBA) during degradation of BAM demonstrated that the first step involved amidase activity. Mass balance calculations and thin-layer chromatography coupled with autoradiographic detection indicated that degradation of DCBA and at least one unknown metabolite may comprise a bottleneck for BAM mineralisation by Aminobacter spp. The study thus provides novel information about the BAM degradation pathway and points to the involvement of unknown intermediate metabolites in degradation of this important groundwater contaminant.

Using 2,6-dichlorobenzamide (BAM) degrading Aminobacter sp. MSH1 in flow through biofilters—initial adhesion and BAM degradation potentials

“…Three times lower density resulted in 94 % degradation of 2.8 μg/L BAM (Table 3), giving that each cell in those filters then degraded on average~10 −12 μg BAM per min. Previous batch experiments with liquid pure cultures have shown that each MSH1 cell may degrade 10 −10 μg BAM per min at 20°C with a BAM concentration of 123 μg/L (Simonsen et al 2012). Only~1 % of this degradation rate was achieved in our filters, showing that it may be difficult to compare results from shaking flasks containing pure liquid cultures with those obtained from column studies.…”

“…Furthermore, an additional degradation product not visible on UPLC-UV was visible and showed a 14 C activity of~3 % of the added 14 C-BAM in filters containing both old and "fresh" cells. This degradation product has previously been detected using TLC, but the exact structure is still not known, although it has been described as one or more very polar compounds formed after cleavage of the aromatic ring (Simonsen et al 2012). Approximately 17 % of the added 14 C-BAM was found as 14 C-HCO 3 − , representing a minimum mineralization, as losses of 14 CO 2 and incorporation into biomass could not be quantified.…”

“…5 (Table 1). Two hours later, 45 mL was sampled from each outlet and preconcentrated to 900 μL on an Oasis MAX multifunction SPE column previously found to be suitable for preconcentration of unknown BAM degradation products and then analyzed for nonvolatile 14 C compounds using a normal-phase TLC method with autoradiographic detection (Simonsen et al 2012). Furthermore, 14 C-HCO 3 − in the outlet water was determined as follows: a 20-mL glass LSC vial was added 40 μL HNO 3 (65%), and a glass tube, with 1 mL 1 M NaOH; outlet water (2 mL) was added to the vial; and the lid was closed immediately thereafter and left on overnight.…”

“…The isolated soil bacterium Aminobacter sp. MSH1 degrades BAM very effectively with up to~60 % mineralization to CO 2 (Sørensen et al 2007;Simonsen et al 2012). In the present study, attempts were made to inoculate laboratory-scale model filters with MSH1.…”

Kinetics and Yields of Pesticide Biodegradation at Low Substrate Concentrations and under Conditions Restricting Assimilable Organic Carbon

“…This pollution can impair water quality (1, 2) and lead to significant economic effects when pollutant concentrations warrant closure or mandated remediation of a contaminated drinking water source (3,4). Exploitation of microbial processes has long been considered an attractive option to remediate contaminated water resources (5).…”