Advancing Shewanella-based whole-cell biosensors: A comprehensive review on heavy metal detection

Whole-cell biosensors are widely used to detect the toxicity of heavy metals owing to their ease of culturing, low cost, and rapid response times. Shewanella species, electrically active microorganisms capable of extracellular electron transfer (EET), are often employed as sensitive bio-elements in biosensors. However, the EET efficiency and heavy metal tolerance of Shewanella species are influenced by various environmental factors, such as pH, carbon sources, and ion concentrations. These influences lead to challenges such as insufficient electron signal output and reduced tolerance or recovery after exposure to metal ions, compromising the stability and sensitivity of Shewanella-based biosensors. Notably, current Shewanella-based biosensors have demonstrated detection limits as low as 0.1 μM (Hg^2 +, Pb²⁺, Cd²⁺), with response times ranging from 5 min to 30 min depending on the sensor configuration. To address these issues, this review comprehensively examines the effects of key environmental factors and heavy metal exposure on the sensing performance of Shewanella spp. Furthermore, it highlights emerging strategies to enhance sensor performance, including the genetic engineering of Shewanella and material modifications to improve electron transport and overall sensor efficiency. This review provides novel insights into the principles underlying Shewanella-based toxicity biosensors through the lens of EET while also shedding light on recent advancements in the development of whole-cell biosensors utilizing Shewanella species.