A fluorescent, supramolecular chemosensor to follow steroid depletion in bacterial cultures

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 cucurbit[8]uril (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. Graphical abstract Steroid depletion by bacterial cultures can be followed by fluorescence spectroscopy using a supramolecular chemosensor based on berberine and cucurbit[8]uril.