Freeze-drying as suitable method to achieve ready-to-use yeast biosensors for androgenic and estrogenic compounds

• Freeze-drying immobilization to obtain “ready-to-use” versions of yeast biosensors.
• Immobilized yeast cells stored at −18 °C retained viability at least up to 10 months.
• Sensitivity towards androgens and estrogens was comparable to standard assays.
• The new method shortens conventional procedures from 3–4 days to 6 h in non-sterile conditions.

Recombinant yeast assays (RYAs) have been proved to be a suitable tool for the fast screening of compounds with endocrine disrupting activities. However, ready-to-use versions more accessible to less equipped laboratories and field studies are scarce and far from optimal throughputs. Here, we have applied freeze-drying technology to optimize RYA for the fast assessment of environmental compounds with estrogenic and androgenic potencies. The effects of different cryoprotectants, initial optical density and long-term storage were evaluated. The study included detailed characterization of sensitivity, robustness and reproducibility of the new ready-to-use versions, as well as comparison with the standard assays. Freeze-dried RYAs showed similar dose-responses curves to their homolog standard assays, with Lowest Observed Effect Concentration (LOEC) and Median effective Concentration (EC50) of 1 nM and 7.5 nM for testosterone, and 0.05 nM and 0.5 nM for 17β-estradiol, respectively. Freeze-dried cells stored at 4 °C retained maximum sensitivity up to 2 months, while cells stored at −18 °C showed no decrease in sensitivity throughout the study (10 months). This ready-to-use RYA is easily accessible and may be potentially used for on-site applications.

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