Living bacterial reactor potently activates tumor immunogenic ferroptosis via cysteine depletion and photothermal therapy

Bacterial combination therapy offers immense promise for treating aggressive "cold" solid tumors, such as triple-negative breast cancer (TNBC). However, the clinical translatability of traditional genetic engineering is often hampered by operational complexity and genetic instability. Here, we developed A-SPB-a non-genetically engineered, multi-functional living bioreactor based on <i>Shewanella oneidensis</i> MR-1 (SO), surface-modified with Prussian blue (PB) nanoparticles and attenuated via deoxycholic acid (DA) treatment. This platform serves as an <i>in situ</i> metabolic factory that "hijacks" the sulfur-metabolism within the hypoxic tumor microenvironment. By actively depleting cysteine, A-SPB not only starves the glutathione (GSH) synthesis pathway but also generates hydrogen sulfide (H₂S) to inhibit the transsulfuration bypass, leading to a dual-pronged collapse of the GSH/GPX4 antioxidant axis and triggering robust tumor ferroptosis. This metabolic sensitization is further amplified by the PB-mediated photothermal therapy (PTT), which generates localized hyperthermia and excessive reactive oxygen species (ROS). Notably, the PTT serves as a dual-functional "bio-switch": it promotes acute tumor ablation while simultaneously triggering bacterial self-lysis to ensure biosafety. This programmed lysis releases a synergistic cocktail of bacterial PAMPs and tumor-derived DAMPs, which effectively remodels the immunosuppressive TME and initiates a potent systemic antitumor immune response. By integrating metabolic reprogramming, sensitized ferroptosis, and on-demand immune activation through simple surface engineering, this study provides a highly translatable and safe paradigm for the next generation of living bacterial therapeutics.