Abstract
The widely used artificial sweetener acesulfame K has long been considered recalcitrant in biological wastewater treatment. Due to its persistence and mobility in the aquatic environment, acesulfame has been used as marker substance for wastewater input in surface water and groundwater. However, recent studies indicated that the potential to remove this xenobiotic compound is emerging in wastewater treatment plants worldwide, leading to decreasing mass loads in receiving waters despite unchanged human consumption patterns. Here we show evidence that acesulfame can be mineralized in a catabolic process and used as sole carbon source by bacterial pure strains isolated from activated sludge and identified as Bosea sp. and Chelatococcus sp. The strains mineralize 1 g/L acesulfame K within 8–9 days. We discuss the potential degradation pathway and how this novel catabolic trait confirms the “principle of microbial infallibility.” Once the enzymes involved in acesulfame degradation and their genes are identified, it will be possible to survey diverse environments and trace back the evolutionary origin as well as the mechanisms of global distribution and establishment of such a new catabolic trait.
Highlights
The potassium salt of acesulfame, named acesulfame K (ACE-K; CAS = 55589-62-3; E950 in the EFSA list of food additives) is an artificial sweetener that was discovered in 1967 and first described by Clauß and Jensen (1973)
Evidence of ACE biodegradation in conventional biological wastewater treatment was shown by Castronovo et al (2017), who detected removal between 59 and 97% in 13 municipal wastewater treatment plants (WWTPs) and identified sulfamic acid (SA) as the mineralization product
In all cultures growing on ACE but not in the corresponding control experiments with 3-hydroxybutyrate, acetoacetamide-N-sulfonic acid (ANSA) was detected in the culture supernatant and identified by its exact mass and fragment ions according to Castronovo et al (2017)
Summary
Tran et al (2014) suggested co-metabolic ACE degradation by autotrophic ammonia-oxidizing bacteria, while Gan et al (2014) discussed a combined effect of photolysis and biodegradation contributing to ACE transformation under environmental conditions Taken together, these studies have shown that ACE might be slowly degraded in soils and aquifer sediments but substantial removal in WWTPs was not evident until 2016. Evidence of ACE biodegradation in conventional biological wastewater treatment was shown by Castronovo et al (2017), who detected removal between 59 and 97% in 13 municipal WWTPs and identified sulfamic acid (SA) as the mineralization product. Further enrichments inoculated directly with sludge samples from the treatment wetland (100 mg/L or 1 g/L ACE-K as sole carbon source in Brunner medium DSM 462, 30°C) resulted in the isolation of several other strains identified as Bosea sp. In all cultures growing on ACE but not in the corresponding control experiments with 3-hydroxybutyrate, acetoacetamide-N-sulfonic acid (ANSA) was detected in the culture supernatant and identified by its exact mass and fragment ions according to Castronovo et al (2017)
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