A fluorescent, supramolecular chemosensor to follow steroid depletion in bacterial cultures
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Steroids have been identified as endocrine-disrupting agents, which are thought to impact the fertility of aquatic organisms and may even have direct effects on humans. The removal of steroids from wastewater is therefore essential, and this is most efficiently achieved by microbial treatment. We report herein a simple fluorescent method to identify microorganisms that are capable of steroid degradation and to optimize the conditions for steroid removal. The method is based on the supramolecular macrocycle cucurbituril (CB8), which can bind either the fluorescent dye berberine or a steroid in their inner cavity. In absence of steroid, the cavity is free to bind the dye, leading to a strong increase in fluorescence. In contrast, in the presence of steroid, the dye is displaced into the bulk solution. This principle affords a stable (no thermal or photodegradation was noted), fluorescent chemosensor (excitation ca. 450 nm, maximum emission at 525 nm), which can detect testosterone at concentrations > 0.7 μM. We show that this displacement principle can be applied to follow the removal of micromolar concentrations of the steroid testosterone from a bacterial culture of Buttiauxella sp. S19-1. The reliability of the chemosensor in screening applications is demonstrated by an excellent Z-factor, which was in the range of 0.52 to 0.74 for all experiments carried out with this assay.
KeywordsFluorescence Supramolecular recognition Cucurbiturils Assay method Marine bacteria Steroids
The authors would like to thank Prof. Dr. Edmund Maser and Dr. Guangming Xiong (Institute for Toxicology and Pharmacology for Natural Scientists, Christian-Albrechts-Universität Kiel, Germany) for providing Buttiauxella sp. S19. This project was funded by the Helmholtz Graduate School for Polar and Marine Research (POLMAR) and the Deutsche Forschungsgemeinschaft (grant numbers UL 169/6-1 for M.U., NA 686/11-1 for W.M.N., and HE 5967/4-1 for A.H.).
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Conflict of interest
The authors declare that they have no conflicts of interests.
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