Development and application of a highly specific whole-cell biosensor for supersulfide detection in environmental...

Supersulfides are a class of sulfur compounds in either zero-valent or monovalent negative states, such as elemental sulfur, inorganic polysulfides, and organic polysulfides, and they play crucial roles in biological systems, environmental sulfur cycling, and Li-S batteries. However, accurate quantification of these compounds remains challenging due to their reactive nature and structural complexity. Here, we report the first whole-cell biosensor for the specific detection of supersulfides using the supersulfide-sensing repressor BigR of Agrobacterium tumefaciens (AtBigR). This novel biosensor system shows exceptional selectivity for supersulfides with negligible response to H₂S, thiosulfate, and glutathione. Through systematic optimization of the AtBigR-based whole-cell biosensor (AtBigR-WCB), we developed a biosensor with negligible background leakage and high sensitivity, capable of detecting supersulfides at micromolar levels. We successfully applied AtBigR-WCB to quantify supersulfide contents in marine sediments from diverse seafloor topographies and lithium polysulfides in lithium-sulfur battery electrolytes. Widespread supersulfide accumulation was detected in deeper layers of marine sediments across various environments. Additionally, the optimized AtBigR regulatory system was a novel, low-leakage regulating system, which offers a new type of gene-regulating system with potential applications in synthetic biology. Our work establishes a new platform for quantifying supersulfides, which is helpful to further our understanding of supersulfides in biology, environments, and lithium sulfur batteries.