Abstract
Aminobacter sp. MSH1 (CIP 110285) can use the pesticide dichlobenil and its recalcitrant transformation product, 2,6-dichlorobenzamide (BAM), as sole source of carbon, nitrogen, and energy. The concentration of BAM in groundwater often exceeds the threshold limit for drinking water, requiring additional treatment in drinking water treatment plants or closure of the affected abstraction wells. Biological treatment with MSH1 is considered a potential sustainable alternative to remediate BAM-contamination in drinking water production. We present the complete genome of MSH1, which was determined independently in two institutes at Aarhus University and KU Leuven. Divergences were observed between the two genomes, i.e. one of them lacked four plasmids compared to the other. Besides the circular chromosome and the two previously described plasmids involved in BAM catabolism, pBAM1 and pBAM2, the genome of MSH1 contained two megaplasmids and three smaller plasmids. The MSH1 substrain from KU Leuven showed a reduced genome lacking a megaplasmid and three smaller plasmids and was designated substrain MK1, whereas the Aarhus variant with all plasmids was designated substrain DK1. A plasmid stability experiment indicate that substrain DK1 may have a polyploid chromosome when growing in R2B medium with more chromosomes than plasmids per cell. Finally, strain MSH1 is reassigned as Aminobacter niigataensis MSH1.
Highlights
The occurrence of organic micropollutants in different water compartments threatens both ecosystem functioning as well as future drinking water supplies[1]
The first step of BAM-mineralization involves the hydrolysis of BAM to 2,6-dichlorobenzoic acid (2,6-DCBA) by the amidase BbdA encoded on the 41 kb IncP1-β plasmid p BAM17
To come to full management of bioaugmentation using MSH1 in drinking water treatment plants (DWTPs) biofiltration units aiming at BAM removal, more knowledge is needed on the physiological as well as genetic adaptations of MSH1 when introduced into the corresponding oligotrophic environment
Summary
The occurrence of organic micropollutants in different water compartments threatens both ecosystem functioning as well as future drinking water supplies[1]. The strain mineralizes BAM at trace concentrations[6] and invades biofilms of microbial communities of rapid sand filters used in drinking water treatment plants (DWTPs)[10]. Since the strain is being studied for several years in different laboratories, the genome was independently sequenced in two different laboratories from different institutes, i.e., KU Leuven, Belgium and Aarhus University, Denmark to infer possible changes This was the case with the Aarhus strain (DK1) showinga single chromosome and seven plasmids, including the two previously described catabolic plasmids pBAM1 and pBAM2, while KU Leuven strain (MK1) appears a variant that still contained pBAM1 and pBAM2 but lacked four of the five other plasmids. This supports the hypothesis that MSH1 might have a polyploid chromosome, at least under some growth conditions
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