Surface Colonization and Activity of the 2,6-Dichlorobenzamide (BAM) Degrading Aminobacter sp. Strain MSH1 at Macro- and Micropollutant BAM Concentrations

Abstract

Aminobacter sp. MSH1 uses the groundwater micropollutant 2,6-dichlorobenzamide (BAM) as a C and N source and is a potential catalyst for biotreatment of BAM-contaminated groundwater in filtration units of drinking water treatment plants (DWTPs). The oligotrophic environment of DWTPs including trace pollutant concentrations, and the high flow rates impose challenges for micropollutant biodegradation in DWTPs. To understand how trace BAM concentrations affect MSH1 surface colonization and BAM degrading activity, MSH1 was cultivated in flow channels fed continuously with BAM macro- and microconcentrations in a N- and C-limiting medium. At all BAM concentrations, MSH1 colonized the flow channel. BAM degradation efficiencies were concentration-dependent, ranging between 70 and 95%. Similarly, BAM concentration affected surface colonization, but at 100 μg/L BAM and lower, colonization was similar to that in systems without BAM, suggesting that assimilable organic carbon and nitrogen other than those supplied by BAM sustained colonization at BAM microconcentrations. Comparison of specific BAM degradation rates in flow channels and in cultures of suspended freshly grown cells indicated that starvation conditions in flow channels receiving BAM microconcentrations resulted into MSH1 biomasses with 10-100-times reduced BAM degrading activity and provided a kinetic model for predicting BAM degradation under continuous C and N starvation.

Genetic (In)stability of 2,6-Dichlorobenzamide Catabolism in Aminobacter sp. Strain MSH1 Biofilms under Carbon Starvation Conditions

“…Based on biovolume calculations of MSH1-GFP biofilms, specific BAM degradation rates at micropollutant concentrations were the same in both flow chamber experiments (with and without reduction of AOC) as those reported by Sekhar et al (10) and hence were 100-fold lower than those found for fresh cells in suspended batch conditions. The instability of the Dcba ϩ phenotype might be a cause of reduced activity, since it will result in cells that cannot gain energy from the available BAM.…”

“…Below feed concentrations of 100 g/liter BAM, the growth of MSH1 is due mainly to residual assimilable organic carbon (AOC) present in the minimal medium. Moreover, MSH1-specific BAM-degrading activity was reduced 100-fold compared to that of freshly grown cells due to C and/or N starvation (10). A similar reduction in specific BAM-degrading activity was found in a DWTP pilot-scale sand filter study that investigated bioaugmentation with Aminobacter sp.…”

“…The bbdD/16S rRNA gene ratio, however, clearly changed. In biofilms originating from the DCBA ϩ inoculum, the bbdD/16S rRNA gene ratios decreased significantly (by factors of 7,10,8,12, and 2 when feeds containing 0, 1, 10, 100, and 1,000 g/liter BAM, respectively, were used). Similarly, biofilms originating from the DCBA Ϫ inoculum became depleted of bbdD when they were grown on 0, 1, …”

“…d MSH1-GFP cell numbers were calculated by dividing the GFP-labeled biofilm biovolume (per cubic micrometer) with the MSH1-GFP cell volume (0.36 (10). Values are averages with standard deviations and were derived from nine image stacks (three image stacks were taken from each of three biofilms).…”

“…Some authors reported the possibility that the production of GFP can exert a metabolic burden on cells that carry gfp, which might, hence, increase catabolic gene loss in the MSH1-GFP population. However, this is unlikely, since Sekhar et al (10) showed growth rates and biofilm formation of MSH1-GFP that did not differ from those of the wild-type strain. As such, no metabolic burden was expected from GFP production, which is in agreement with observations for other organisms (22,23).…”