Development of Highly Sensitive, Automatized and Portable Whole-Cell Hg Biosensor Based on Environmentally Relevant Microorganisms

Whole-cell biosensors are still the method of choice when measuring bioavailable mercury, though their implementation in environmental monitoring is limited by low sensitivity, lack of portability and use of environmentally irrelevant bacteria. To address these issues, we have engineered a new luminescence-based whole-cell mercury biosensor, as part of a standalone fully automated portable device. Our method allows the incorporation of any environmentally relevant bacterial cell, which has been modified to translate the concentration of biologically available mercury into a dose-dependent luminescent signal. The use of environmentally relevant bacteria, Pseudomonas putida for fresh waters and Aliivibrio fischeri for salt waters, demonstrated that environmental samples will not exhibit toxic effects, when appropriate microorganisms are implemented. Additionally, by assuring efficient aeration of the medium and thus sufficient oxygenation of sensor cells during generation of the luminescence signal, we obtained a clear dose-dependent response and observed an increased sensitivity of the method up to 100 times (the limit of detection [LOD] was determined to be as low as ∼10 ng L⁻¹). Finally, using our automated device, we demonstrated that in the environment the biologically available fraction of mercury can (1) represent an important part of the total mercury content (40–70%) and (2) it can correspond to the changes of total mercury content, which results in higher bioavailability of mercury closer to the source of mercury contamination.